TYPES OF ELECTRIC CIRCUIT&INSTRUCTION

Types of Circuits - Short Circuits

A short circuit is a circuit in which the electricity has found an alternative path to return to the source without going through an appropriate load. You can demonstrate this easily by taking a fine piece of wire and connecting it to both the positive and negative terminals of a small battery. The wire will heat instantly and probably melt. In most circuits, this high amperage represents a dangerous situation that could cause a fire or electrocute someone.

border=0 v:shapes="_x0000_s1027">Consider the circuit shown where the source is the outlet, the path is the extension cord, and the load is the drill. If the wire inside the drill comes loose and touches the other wire, a new path exists where the current can return to the source without going through a load the drill motor. Thus, the name short circuit because the electrons have found a shorter path to take to get back to the source.

Another type of short circuit occurs when some conductive object accidently gets into an overhead power line. If the object touches both the lines at the same time, the electricity has a short circuit path available to return to the source before it goes to the customer's electric service. If the object is connected to the ground, the earth can act as a short circuit path. Additional information about short circuits and electrical safety is covered in the Safety section.

Types of Circuits - Open Circuits

An open circuit is a circuit where the path has been interrupted or "opened" at some point so that current will not flow. An open circuit is also called an incomplete circuit.

An open circuit could be intentional or un-intentional. An intentionally open circuit would be the circuit to the lights in the room that are turned off. There is no closed path available for the electricity to flow to the lights because the switch is in the "off" position which "opens" the path the electricity would normally flow through.

An example of a circuit that is un-intentionally open is when a circuit breaker operates due to too much current on the circuit and shuts the circuit off. The common electrical industry terminology would be to say that the circuit breaker or fuse "opened" or tripped the circuit. It did this by "opening" the switch in the circuit breaker.

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Types of Circuits - Power Circuits

A power circuit is defined as any circuit used to carry electricity that operates a load. This may seem like a simplistic definition but it is important to distinguish power circuits from control circuits since they serve different purposes.

A circuit with an outlet for the source, two wires for the path, a switch for the control device and a motor for a load is a good illustration of a power circuit. When the switch is closed, the electrons flow through the path and the electrons go directly through the motor windings and cause the motor to operate. The only circuit control in this circuit is the switch wired directly in series with the motor. There is no separate control circuit associated with this power circuit. Most lighting and receptacle outlet circuits in a house are power circuits since they only provide power to devices when the devices operate, and the circuit control is part of the power circuit.

Types of Circuits - Control Circuits

A control circuit is a special type of circuit used to control the operation of a completely separate power circuit. Consider a 1,000 horsepower, large industrial motor driving a water pump. The motor is connected to a high voltage electrical supply of 2,400 volts.

When this motor is energized, it must draw enough current to get the water moving and it is common for a motor to draw about six times its normal operating current for a short period of time. When we were talking about controlling light bulbs, it was safe to operate a simple switch on the wall. But now this large amount of current flowing when the motor starts can be troublesome. The first concern is the operator's ability to safely close the switch. The second concern is that when the operator opens the switch to turn the motor off, the electricity will continue to try to complete the path. This will tend to arc between the contacts of the switch as it is opened. This arcing is not only dangerous but also damages the switch by severely burning the contact points. A control circuit is used to ensure that the motor is started and stopped in a safe manner for both the operator and the equipment.

A common control circuit example is the thermostat to the air conditioner in a house. The thermostat is part of a low-voltage control circuit that controls a relay that actually energizes and de-energizes the power circuit to the air conditioning compressor.

Types of Circuits - Grounded Circuits

Have you ever touched an electrical appliance and felt a shock? It probably was an un-grounded device. And, you certainly have been warned about touching electrical appliances when your feet or hands are wet. While not common a few decades ago, almost all household equipment today is grounded with a round third prong, and there are even detectors in modern bathroom electrical systems that detect and interrupt circuits whenever even a small amount of current is flowing through that ground. These devices are called ground fault circuit interrupters of GFCIs. See the Safety section for more information on grounding and GFCIs.

Grounding is achieved in an electrical system when one of the conductive wires serving as part of the circuit path is intentionally given a direct path to the earth. This is commonly accomplished by connecting one of the circuit wires to the soil or ground by running a wire to a ground rod, a long copper rod driven directly into the soil.

Advantages of grounding one wire of a circuit include safety and reliability. Without grounding, both wires are "hot," meaning the wires are energized at the circuit voltage. If someone touched the conductive part of either wire, they would be exposed to the full circuit voltage. With a grounded circuit, only one wire becomes hot and the other wire is grounded. Touching the hot wire still exposes a person to the full circuit voltage.

In a grounded circuit, we often refer to the electricity traveling from the source to the load on the hot wire and returning to the source on the grounded wire. This is not quite correct since AC current changes direction 60 times a second.

Electrical power suppliers also commonly ground one of the wires on the electrical distribution system by connecting it to the ground. This is done by running a copper wire from a clamp around the wire to a ground rod at the bottom of the pole. This "grounded" wire has several different names including the neutral wire, and grounded neutral wire.

Grounding electrical utility distribution circuits is also done for safety and reliability reasons on the electrical system. If the electric system was not grounded, lightning would follow the path of the wires either through the customer's appliances or the utility's wires to the generator.

Remember, electrical system grounding is not the same as electrical equipment grounding. Electrical equipment is grounded using a third wire run to an appliance or device and connected to the third "round prong" of the outlet.

Human Response

Electricity can be harmful -- even fatal -- and should always be treated with the greatest of respect and care. But when a person does come in contact with electricity, that person will actually feel the current flow through his or her body. This current flow is what causes a variety of responses, ranging from faint tingling sensations to death.

Perception

Perception is defined as the lowest level at which people can still perceive electrical current. Typically, the level of perception is 1/100 amp, or 1 milliamp. Any lesser amount of current would not be felt by most people. Slightly above this level, a mild tingling sensation is felt and the person "perceives" that electricity is there. Your tongue is usually the most sensitive organ and can easily sense the current flow from a small battery.

Let Go

Electricity flowing through our bodies affects our muscles and nervous system. The "Let Go" Threshold is the level at which we begin to lose control of our muscles. For most people this threshold is about 15 milliamps. At or above this level, the current flowing through our bodies interferes with our muscles' ability to function. You may have heard of people not being able to let go of an object while being shocked. This is because the electricity causes muscles to contract. Our muscles will remain contracted until the current is removed. Pain is generally felt at this level.

Burns

Electrical contacts can cause burns due to current flow through the body. At currents higher than 50 milliamps, the heat produced is enough to burn the human skin and flesh tissue.

Electrical burns may be of two types - -those on the outside of the skin where the electricity entered or left the bodies, and those on the inside of the body where the electricity flowed through the body.

Electrocution/Fibrillation

At levels of current flow exceeding 1/10 of an amp or 100 milliamps, the heart stops. This is called fibrillation. A person may survive an electrocution if his or her heart can be started again. This is why CPR is such an important skill in the CPR on SAM Graphic

electrical industry.

Resistance of Humans

Humans are conductors of electricity and have electrical resistance similar to any other material. The human body's resistance to current flow varies depending on:

§ internal and external moisture;

§ exposed sub-epidermal tissue;

§ and skin thickness.

Human resistance is about 10,000 ohms on the high side and as little as 1,000 ohms if the person is wet. Remember, ohms is the unit of measure of a material's resistance or impedance to current flow. Current flow is obviously higher as the resistance goes down.

As an example, let's see how much current flows through a person if he or she contacts a typical 120 volt household circuit. On the high side, with human resistance around 10,000 ohms, we can compute the current flow by dividing the voltage, 120, by the resistance, 10,000. This yields .012 amps, or 12 milliamps.

This is well above the perception level of 1 milliamp, and slightly below the 15 milliamp "let go" threshold. We feel it, but we can let go and have no lasting physical damage.

If we are wet or standing in water, we become a much better conductor, thereby offering less resistance. The current flow is again found by dividing the voltage, 120, by the lowered resistance of 1,000 ohms, which yields 0.12 amps, or 120 milliamps, of current flow. This is easily enough current to send the heart into fibrillation and cause electrocution.

Outdoor Safety

Overhead Power Lines
Underground Power Lines
Outdoor Equipment
Antennas/Ladders
Recreational Safety
Job Site Hazards
Electrical Emergencies

Overhead Power Lines

There are several things to remember about overhead power line safety. First and foremost is that overhead power lines are NOT insulated. They will energize anything that comes in contact with them and provides a conductive path to the ground. Utilities elevate lines on power poles to higher levels than people can normally reach. However, someone can still lift long metal devices, such as ladders, TV antennas, or other conductive objects into the lines.

It is also important to never approach, or try to move, a power line that has fallen down to the ground. In fact, keep at least 10 feet away for safety's sake. Similar rules apply to sagging lines. National codes dictate the minimum distances from the ground for power lines carrying various voltages. If you suspect that a power line is hanging down too far, let the utility know.

Guy wires are attached to some utility power poles to keep them upright. It is a good idea to stay clear of all guy wires. Even though guy wires are not electrically charged, they are in direct contact with the ground and become an easy path for an electrical current.

In short, remain clear of all overhead power lines and their supporting structures.

Underground Power Lines

Electrical circuits are generally placed underground to protect the lines from high winds, ice and other damaging elements. Underground installation also improves aesthetics, but is usually more costly. For this reason, most utilities will install underground lines at the customer's request and cost.

Underground power lines of any type have very thick insulation. In addition, National Codes dictate the depth, below ground, these lines must be buried. Some low voltage underground circuits could be as shallow as 18 inches, while most higher voltage circuits will be deeper than 24 inches.

If there are underground electrical circuits on your property, pay attention to where they are located. Never dig holes for planting trees, shrubs or other landscaping without determining the location of underground electrical lines. In general, most electrical lines are buried deep enough to make gardening safe, but to be sure, always check with the utility before planting, placing bushes or trees, and digging post holes for fences.

Many utilities belong to organizations that map and record the locations of ALL underground lines like electrical, cable, telephone and gas lines. Either the utility company or the underground records company can come to your location and mark the location of underground lines so you know where they are.

If a utility has installed underground power lines in your area, several large steel boxes containing transformers will be located at ground level around your neighborhood. While these high voltage transformers are quite safe when the enclosures are closed and locked, for safety's sake, please keep your distance. If one is found opened or damaged, call the utility company immediately.

Outdoor Equipment

Outdoor electrical equipment must operate under more severe environmental conditions -- such as excessive moisture and sunlight -- than indoor electrical equipment. For this reason, outdoor equipment is specifically designed to operate safely and meet any special requirements of outdoor operation.

Antennas/Ladders

It is critical that we practice good safety around power lines, whether at work or around our homes. When raising or positioning metal ladders, pool skimmers or scaffolds, first check the area for overhead lines. Also, be sure there aren't power lines running through or near trees if you are trimming branches.

If you're installing an antenna, whether for radio, television or CB use, watch for overhead electric lines. Keep a safe distance, at least one and a half to two times the height of the antenna and mast assembly, between the power line and your antenna. Always prepare before starting work by becoming aware of all the lines around you. Plan the installation based on this knowledge. If you lose control of an antenna, and it begins to fall toward power lines, let it go.

Recreational Safety

Even though power lines are installed high overhead, they still pose a potential danger to children. They need to be educated well enough to know to stay off and away from any type of electrical facility, be it the towers, poles or the fence around a substation.

Flying kites or other airborne types around utility lines is dangerous. If a kite or toy airplane gets caught in an overhead line, do not attempt to remove it.

Water sports and outdoor recreation can be fun and even more enjoyable when you practice good safety habits. Unfortunately, bare, un-insulated power lines often cross small bodies of water and docking areas.

Watch out for overhead electric lines near boat docks and piers. A sailboat's mast, spar rigging antenna or flag mast could pose potential danger around power lines. When hauling, docking or transporting a boat, be sure to remove or lower metal equipment that could come into contact with overhead electric lines.

Don't forget, water makes a good path for electrical current, so never touch electric switches or wires when you are wet.

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Job Site Hazards

Construction and industrial jobs require special consideration when employees work around electricity and/or utility lines. Federal, state and local regulations specify safe distances for working around power lines. These rules should be strictly adhered to at all times.

When working near overhead lines, state laws generally require that you contact the local utility. In many cases, the utility can temporarily shut off the power, relocate the lines, or assure that adequate power line clearance and safety is maintained. It is also mandatory to check with the utility company before beginning any work on a job site that entails trenching or digging to confirm the locations of any underground power lines.

Tall equipment such as cranes, draglines or scaffolds should be positioned the required distance away from overhead utility lines. If any equipment strikes an electric line, the operator should remain inside the cab until someone gets help. If the equipment is electrically charged, the operator must not touch the equipment and the ground at the same time, or he or she will get electrocuted. Let trained rescue teams remove the operator safely.

Electrical Emergencies

A downed power line is potentially hazardous. Always assume a fallen wire is "live" or "hot" even if it looks harmless. If the wire is energized or "live," it will electrically charge anything that comes into contact with it. Never touch anything the fallen wire has been in contact with. Stay clear, warn others around you to keep away and call the local utility company immediately. If someone is harmed by an outdoor wire, call an ambulance, notify the police or fire department, and call the local utility company immediately. Stay away from the wire and the person who was hurt. Do not touch them because they can still conduct electricity through you.

If you see someone in a car with a fallen power line contacting it, do not approach the car and try to help the person out. If you touch the car, you complete the path for the electricity to flow into the ground through your body. Instead, tell the person to stay in the car and remain calm, and that you will contact and alert the necessary emergency people.

If you're inside a car and a live wire comes in contact with your vehicle, stay inside where you are safe and wait for help. The tires of the car provide insulation between the car and ground, and should protect you against electrical shock while you remain inside the vehicle. If you touch the vehicle and the ground at the same time, you will complete the path for electricity to flow between the downed wire and the ground, right through your body. If you must get out, a method that can work well is to stand on the edge of the inside of the vehicle and leap as far from the car as possible onto the ground.

Indoor Safety

Electrical safety sense begins inside and around your home, office or workplace. Before you buy or use any appliance, be sure it is approved by the UL or Underwriter's Laboratory label. Ensure that there is adequate, safe power available to operate electrical devices in your home or workshop.

Check Equipment

Check for frayed cords, broken plugs or damaged wires on all appliances. These hazards can cause an electrical shock or fire. Never touch electrical circuits, cords or plugs with bad insulation unless you are absolutely sure the power if OFF. If an appliance smokes or sparks, or if you feel a "tingle" or shock when operating an appliance, don't use it. Have the equipment replaced or repaired by a qualified service representative.

When using appliances with removable cords, always connect the cord to the appliance first, then plug it into the wall outlet. When disconnecting the appliance, unplug it from the wall outlet first, and then remove the cord from the appliance. Be sure to pull the plug, not the cord, because you could damage the wiring in the cord or its insulation.

Wet/Damp Areas

Remember this simple rule: water and electricity are a potentially lethal combination. Stay away from water when using electrical appliances -- standing in a tub of water or shower and using a blow dryer or curling iron could result in electrocution. Many consumer products such as hair dryers, electric power tools, TV sets, radios and small kitchen appliances can easily become electrical hazards if they come in contact with water. They are not designed to operate when wet.

The best idea is not to use these appliances anywhere near basins, tubs or sinks that hold water. If an appliance does contact water, say the blow dryer drops into a sink full of water, do not reach into the sick of water after it. This could cause an electrocution. Unplug the blow dryer or turn the electricity off at the fuse or breaker box before you retrieve the blow dryer from the sink, even if

the dryer is in the "off" position.

Metal Objects

Do not stick or poke metal objects into any electric appliance while plugged in for any reason. A common mistake is using a fork to retrieve a jammed piece of bread from the toaster. JUST DON'T DO IT! Metal is a good conductor of electricity, and touching the inside of an electrical appliance with a metal object could get you electrocuted. Unplug the toaster first, then retrieve the bread. Even when replacing a light bulb, the safest route is to unplug the lamp or light fixture first before removing and replacing the old bulb.

Electrical Emergencies

If an appliance catches fire, try to unplug it if possible. Never throw water on an electrical fire. Use a dry chemical CO2 fire extinguisher or even household baking soda to put out the fire.

If someone comes in contact with an indoor electrical circuit, immediately shut off the power at its source. Don't make contact with the victim. Touching the victim makes you a part of the path for current to flow to ground. Free the person or get the circuit away from them by using items made from nonconductive materials, such as wood or rope. Make sure you are standing on a dry surface and that your hands are not wet. Call emergency medical help to administer medical attention and an electrician to check or repair the circuit SAM Shutting Off Power Graphic

as soon as possible.

Grounding

Grounding electrical circuits is a safety practice that enables electricity to take an alternate path back to the breaker box when an electrical device or appliance short circuits. Without a grounding path, the current would flow through someone that was holding the appliance. The grounding wire in a circuit is connected to the third pole in a typical household receptacle.

The grounding wire in this power drill connects to the third prong on the plug and the drill's metal case. This connection is tied back to the breaker box and subsequently to a grounding rod driven deep into the ground.

In the event of a short circuit, the electricity can follow two available paths. The easy path is through the case of the drill and the grounding wire to the breaker box. The harder path is through the person using the drill. Without the grounding wire, the current would flow through the person using the drill since there is no other possible path for the current to follow. This could be catastrophic.

Grounded vs. Grounding

The terms grounded and grounding are very similar, but their meanings are quite different.

In any electrical circuit, there are two wires needed to complete any circuit. One is called the "hot wire" and the other is called "neutral" or "grounded". Sometimes the neutral wire is referred to as a grounded wire. It is most correctly referred to as a "grounded neutral conductor," but most times referred to as "the neutral" or "the ground wire".

Since the neutral or grounded wire is a necessary part of the electrical path, grounded wires carry electrical current under normal operating conditions. A grounded wire is required by the National Electrical Code to be white or gray in color on the customer side of the meter. Grounded wires on the utility side of the system do not generally have insulation.

A "grounding" wire on the other hand is a safety wire that has intentionally been connected to earth. The grounding wire does not carry electricity under normal circuit operations. It's purpose is to carry electrical current only under short circuit or other conditions that would be potentially dangerous. Grounding wires serve as an alternate path for the current to flow back to the source, rather than go through anyone touching a dangerous appliance or electrical box.

Confusion arises because it is commonly referred to as a ground wire even though it is more correctly called a "grounding" wire. Some people will refer to this wire as the "case ground" since this wire is typically connected to the cases or outer parts of electrical boxes and appliances and tools.

The grounding wire is required by the National Electrical Code to be a bare wire, or if insulated, a green or green with yellow colored insulation.

3-Prong Outlets

The standard 3-prong receptacle is called a grounding receptacle because it allows a grounding wire to be connected from the electrical circuit to the appliance. The grounding wire is connected to the third prong of the plug. When a 3-prong plug is plugged into the receptacle, the grounding wire is connected to the prong and provides a continuous grounding path from the appliance back to the breaker box. This grounding path serves as a primary safety means if there is a short circuit or other damage to the electrical circuit or appliance. The grounding wire in the circuit and on the appliance or tool is not required to make the appliance work.

Replacement Outlets

When replacing a 3-prong grounding-type outlet or plug, be sure to replace it with another grounding-type outlet or plug. It may be tempting to replace a worn or frayed 3-prong plug on an appliance or tool with a cheap two-prong plug from the local hardware store. But since the two-prong plug makes no allowance for connection of the grounding wire, the appliance will no longer Replacement 3-prong Outlets

have a grounding path. This now makes using the tool or appliance hazardous

2-Prong Outlets

Many older homes and businesses built and wired in the early 1900s were wired with "grounded" electrical systems that have no grounding wire. You may have encountered these older electrical systems in a building where the electrical outlets only had "two-prong" plugs. There is a hot wire running to the outlet and a grounded wire from the outlet back to the breaker box in these electrical systems. There is no grounding wire in these systems.

Today, building and wiring codes, including the National Electrical Code, recognize the need for grounding wires and require them to be installed during remodeling projects or new construction. The older systems that contain no grounding conductor are sometimes referred to as "un-grounded systems." This means they contain a white, insulated grounded conductor but no bare or green grounding conductor

Grounding Adapters

When an appliance or tool with a 3-prong grounding plug needs to be plugged into a 2-prong outlet, an adapter is commonly used. The adapter accommodates the 3 prongs on the grounding type plug and the two prongs on the receptacle. Adapters have either a green wire or small green metal tab that allows the adapter to be grounded. By connecting the green wire or green metal tab to the electrical system ground, the grounding path remains intact. You can connect the green wire to the cover plate screw on the outlet. If the electrical box is grounded, this will also provide an effective grounding path.

If the electrical box is not grounded, connecting the wire really serves no purpose since it will not be connected to anything.

When using an adapter, make sure the grounding wire is connected to a known grounding source. You should never cut the grounding wire off an adapter, or cut the grounding prong off of a 3-way plug. Any action you take to make it more convenient simply defeats the safety purpose of grounding. Even though an appliance will operate without a grounding conductor, the appliance is not safe if it fails.

Replacement Outlets

When replacing a 2-prong non-grounding type outlet or receptacle, it must be replaced with another two-prong receptacle or a "Ground Fault Circuit Interrupter". Never replace a two-prong with a three-prong receptacle. This would give the false impression that a grounding wire was available.

The National Electrical Code gives several options for replacement of 2 prong receptacles. Refer to the section on "Ground Fault Circuit Interrupters" in this program for more information concerning their operation.

Double Insulation

Many of the newer small electrical appliances and tools do not have a the third grounding prong on the plug. Typical examples are blenders, coffee makers, blow dryers, drills, and other power tools. Appliances and tools of this type are called "double insulated". They have two levels of insulating materials between the electrical parts of the appliance and any parts on the outside that you touch.

The primary difference between a drill with a 3 prong plug and a drill with a 2 prong plug is the drill case material. If the drill case material is conductive, in other words, is made of some kind of iron or ferrous material, then the drill must have a grounding conductor and 3 prong plug.

Double insulation construction of appliances and tools allows the manufacturer to produce a lower-cost product. Double insulated appliances and tools are generally found around the home while their grounded counterparts are more likely to be found in commercial and industrial operations where they encounter much rougher treatment and more potential for damage.

Overload Protection

Every electric circuit in a wiring system must be protected against overloads. A circuit overload occurs when the amount of current flowing through the circuit exceeds the rating of the protective devices.

The amount of current flowing in a circuit is determined by the load -- or the "demand" -- for current. For example, if a circuit is rated for 15 amps maximum, then a fuse or circuit breaker of that rating will be in that circuit. If the current exceeds 15 amps, the circuit breaker will open up, cutting off any more current flow. Without overload protection wires can get hot, or even melt the insulation and start a fire.

There are two kinds of protection for electrical units that need to be considered. The first is concerned with the protection of the actual electrical wires supplying the circuits against an overload above their carrying capacity. The second type is concerned with protecting the individual appliances and electrical equipment connected to a supply circuit from an overload. Both types of protection involve either fuses or breakers, but are based on different ideas and objectives.

How Overloads Occur

Overuse of extension cords and multiple plug adapters on the same circuit are typical causes of an electrical overload -- by placing too much current demand on the circuit. Running too many blow dryers and curling irons at once is a typical problem when homes have a single circuit serving two bathrooms. In each of these cases, fuses should blow or a circuit breaker should open, which shuts the power off. Circuit overloading is common around the holidays, when more electricity is used around the home for electric decorations.

Signs of overloaded circuits include:

§ Flickering lights

§ Sparks from appliances or wall outlets

§ Warm switch plates or outlets

§ Dimming lights or television sets

A warm extension cord or plug always indicates a potential overload.

Don't make the mistake of trying to eliminate a "fuse problem" by replacing a 20 amp fuse with a spare 30 amp fuse. This may seem to fix the problem because the flow won't blow as frequently. But it creates a terribly dangerous situation! Believe it or not, there are people who have put a penny in the place of a fuse, thinking it would help. But the penny is an excellent conductor and will quickly overload the circuit.

onductor Protection

Every size of electric wire has a maximum safe current-carrying capacity or rating. The current-carrying capacity is slightly different depending on:

§ whether the wire is aluminum or copper;

§ whether the conductors are used individually or in groups;

§ and where the wire or cable is placed

§ out in the open air,

§ direct sun or shade

§ inside a well-ventilated, normally heated building, or

§ near a hot furnace or boiler rooms, etc.

There is a point to all of this specifying current ratings in wires.

The breaker or fuse selected to protect a particular wire size from overload must trip or melt before the current flow will cause conductor heating that could be damaging to the wire or insulation. Depending on the way the interrupting device works, the wire or cable may carry momentary overloads, provided the overload time is very short so that the total heat produced cannot build up to dangerous levels. These are called "slow blow" protectors. But, be aware that a small amount of overheating, repeated numerous times can produce deterioration in the conductor insulation.

Obviously, the idea of placing a penny or other metal object behind a fuse, or taping a breaker down so that it cannot trip, is absolutely foolhardy.

Equipment Protection

Fuses and breakers are also used to protect electrical appliances and equipment from damage or complete burn out due to overload. The fuse or breaker at the breaker box is sized to protect the wire, but is not necessarily sensitive enough to protect a small-use device plugged in on the circuit. In this instance, a fuse or breaker is generally built into the appliance or electrical equipment to protect it from overload.

For example, electric motors draw large in-rush currents when they are starting. A typical motor will draw five times as much current while starting compared to its normal running current. Therefore, a motor that draws 3 amps at full-rated load while running, will draw 15 amps while it is starting. A 12 gauge copper wire used to supply the motor with electricity would normally be protected by a 20 amp fuse or circuit breaker. If the motor locks up and draws 15 amps, this current flow will burn out the motor winding very quickly but not cause a 20 amp fuse or breaker to shut off power to the motor. A second fuse or breaker to protect the motor from overloading is clearly necessary in a situations like this.

Note also that when individual equipment fuses or breakers are used, they are used in addition to the regular circuit protection. The fuse or breaker at the main service panel or sub-panel protects the circuit wire against dangerous overloads. The equipment fuse or breaker protects the individual piece of electrical equipment and adds safety to the system.

How Overloads Occur

Signs of overloaded circuits include:

§ Flickering lights

§ Sparks from appliances or wall outlets

§ Warm switch plates or outlets

§ Dimming lights or television sets

A warm extension cord or plug always indicates a potential overload.

GFCIs

Ground Fault Circuit Interrupters Picture

One of the best ways to protect against electrical shock in your home is to install ground fault circuit interrupters, commonly called GFCI's for short. These devices monitor how much current flows to an appliance on the hot wire and how much comes back on the neutral wire. If the difference is greater than 0.005 amps, a fault is detected, and the GFCI will interrupt the power in a fraction of a second. This level of current has been selected because it is above the human level of perception of electricity but well below the "let-go" level, where loss of muscle control occurs.

Ground Fault Circuit Interrupter Graphic

A GFCI outlet has two buttons on the front: a reset button and a test button. When the test button is pushed, an internal short is placed across the GFCI outlet and should cause the GFCI to trip and shut the power off. The reset button should pop out when this happens, which helps alert someone that the GFCI has operated.

The GFCI is re-energized or "re-set" by pressing in the "reset" button. If the reset button will not hold and the GFCI continues to shut the power off every time the reset button is pushed, this indicates there may be a serious electrical problem that needs attention.

Required Locations

Most people have seen GFCI outlets before in bathrooms. or on the outlet for the office coffee maker. In newer homes, these outlets are commonly seen near kitchen and bar sinks, garages, basements, and outdoors near patios and swimming pools. The one thing all these areas have in common is a damp or wet location. Since electricity and water are a dangerous combination, the GFCI outlets provide an added measure of safety protection in these wet and damp places.

The 1996 National Electrical Code requires GFCI's in all bathroom outlets, all kitchen and bar outlets within 6 feet of a sink, all outdoor outlets that serve patios or decks within 8 feet of the ground, one in the garage, one in a basement, and any outlet within 10 feet of a swimming pool. There are additional requirements in commercial and industrial buildings, primarily on rooftops or other areas where maintenance people have to perform service work in wet or damp areas.

Features

GFCI's are available either as an outlet or as a circuit breaker. The outlets are installed similar to a standard outlet and, depending on how they are wired, can protect just their one location, or be used to protect other standard outlets downstream from the GFCI in the circuit.

The GFCI circuit breaker is installed in the electrical system breaker box and protects every plug or device connected to its particular circuit. The GFCI circuit breaker looks similar to a normal circuit breaker except for the test button on the front of the breaker. When the GFCI breaker trips, it does not indicate whether the breaker tripped from an overload or excessive leakage in the circuit.

One feature of the GFCI outlet is that it can be wired to protect all the standard outlets further downstream in the circuit. If an electrical problem develops on a piece of equipment plugged into a standard outlet with a GFCI upstream, the GFCI trips and shuts off power from the GFCI to everything connected downstream. When GFCI's are wired like this, it is sometimes

difficult to tell where the leak in the circuit is, since any outlet or piece of equipment downstream from the GFCI could cause it to trip.

Since GFCI's do not rely on a grounding wire to operate, they can be installed in older homes having two prong non-grounded outlets, and provide a level of safety heretofore unattainable. The National Electrical Code allows GFCI's to replace a two-prong outlet for this reason. Since a GFCI receptacle has a third grounding plug as a standard feature, this eliminates the need for using grounding adapters.

Nuisance Tripping

GFCI's were designed as a very safe way to interrupt power when any current fault occurs. They are used mostly where smaller electrical devices are plugged in. Since GFCI's are sensitive, they have a tendency to trip frequently. This frequent tripping is referred to as "nuisance tripping," since many people see it as a nuisance. For this reason, it is not a recommended practice to plug refrigerators, freezers, or other large appliances into a GFCI outlet.

Nuisance tripping can also be caused by appliances that are just on the verge of going bad. An electric razor may work fine as long as it is not pressed down hard onto the skin. But when the razor is pressed down, it causes the GFCI to trip. This is an indication the razor may be starting to go bad. Some people experience nuisance tripping problems when they try to use their weed eaters or electric lawn mowers when the lawn is very wet. In addition, thunderstorms

may cause GFCI's to trip.

Circuit Breakers

A circuit breaker is essentially a combination of a thermostat and a switch. The circuit breaker has a bimetal strip which heats and bends during a circuit overload. This bending action trips the breaker and opens the switch, thus breaking the circuit.

As soon as the metal strip cools (about two minutes or so) the breaker can be manually reset completing the circuit again. Most units reset either by flipping a switch or by pushing on the breaker. Since there is no easily removed part like a fuse, they are less likely to be replaced with the wrong size if frequent tripping occurs in a circuit.

Circuit breakers have gained popularity because of their convenience. Their one drawback is that the metallic contacts in some hostile environments can corrode shut so that the breaker does not open the circuit when it should.

Anytime a circuit breaker opens, it is an indication of a problem. The problem should be located and corrected before reclosing the breaker to ensure safety.

Fuses

Fuses are electrical safety devices which contain a "link" that melts at a pre-determined electrical current. The link melts because of the heat produced by excessive amounts of current flowing through it. When the fuse link melts, it opens the circuit and shuts off the current flow.

There are two basic fuse types:

§ plug fuses, sometimes called screw-base fuses;

§ and cartridge fuses.

Plug or screw-type fuses are typically used in smaller sizes up to about 30 amps but are made in larger sizes, too. Cartridge fuses are normally found in very small electrical devices and are also used on high current-carrying circuits over 30 amps or more in electric wiring applications. Both types are made in non- Basic Fuse Types Graphic

delay and time-delay -- also called "slow blow" -- designs.

Plug Fuses

Plug fuses are round fuses which screw into a base in the fuse holder to complete the circuit. A plug fuse contains a strip of soft wire or metal. The strip of metal is designed to carry a given amount of electric current, such as 15 amps. If anything happens causing more current to flow in the circuit than the circuit and the fuse are designed to carry, the metal strip melts or "burns out". This opens the circuit, stopping the flow of current and protecting the wiring.

The threads on the base of the common plug or screw type fuse are the same as found on light bulbs. This base and thread size is commonly referred to as an "Edison base", in honor of Thomas Edison who invented the first light bulb. An Edison base fuse is a plug type fuse having this size and type of base. Edison base fuses are discouraged since they allow any size fuse to be placed in the Edison base which makes it easy to "overfuse a circuit" or electrical appliance.

Cartridge Fuses

The cartridge type fuse gets its name from the shape of the container protecting the fuse link. Instead of screwing the fuse into a base, a cartridge fuse snaps or squeezes in between two holders on each end of the fuse. The ends of the cartridge fuse are metal and connect to the fuse link inside the cartridge. Larger current cartridge fuses commonly have a bayonet end that fits snugly between the jaws of special holders. Many older cartridge fuses were made with replaceable fuse elements so if the fuse link "blew" it could be replaced. The use of replaceable fuse links has largely been eliminated to reduce the chance of installation of an oversized link and overfusing.

Time-Delay Fuses

The time-delay, or "slow blow", fuses were developed for situations where acceptable momentary overloads are encountered, such as starting a motor. As the name implies, this type of fuse will carry an overload several times the normal load for a short period of time without blowing.

The time-delay fuse has two elements. In addition to the "burn out" link of the ordinary fuse, there is a short connector with a spring attached. The connector is held in place by low melting point solder. With momentary overloads of 100 to 200 percent of the fuse rating, neither element is affected. But with a continuous overload, heat builds up in the fuse to a point where the solder melts, releasing the spring which opens the contact. If there is a short

circuit, the "burn out link" melts just as in an ordinary fuse.

Type S/Adapter Fuses

Type S fuses are also called tamper proof fuses because each fuse size has a different base and thread size. These fuses also require the use of a special adapter which is screwed into the standard Edison base of the fuse holder. The adapter has a standard Edison base thread on the outside but a special sized diameter and thread on the inside. It also has a spring barb on the outside that projects into the standard Edison base shell of the fuse holder and prevents the removal of the adapter once it has been installed. The different sized base and thread size is such that a larger size S base fuse cannot be screwed into the adapter. The adapters have amperage ratings the same as the fuses which go in them. If a 20 amp adapter is installed in a fuse holder, it is impossible to use

an S type fuse higher than a 20 amp rating in the adapter.

Lockout / Tagout

Lockout / Tagout is a process which requires placing a lock and a red tag on a switch box that supplies power to other circuits or piece of some electrical equipment. This process is implemented to ensure so no one will activate a locked tagged switch. This procedure is required by the Occupational Safety and Health Administration (OSHA) and has ridged guidelines. These are put in place when performing maintenance or repairs to electrical equipment.

Regulations

Lockout/Tagout is required by the Occupational Safety and Health Administration, or OSHA for short. The Code of Federal Regulation (CFR) 1910.147 titled "Control of Hazardous Energy Lockout/Tagout," describes the OSHA lockout/tagout regulations.

This rule includes information on:

§ The application of procedures

§ Servicing and maintenance operations

§ Requirements and inspections

§ Removal of locks and tags and other related issues

OSHA requires employers to provide adequate training to ensure employees understand the purpose and function of the lockout/tagout program. And that employees possess the knowledge and skills required for the safe application, usage, and removal of locks and tags.

Procedures

There are nine steps involved in the lockout/Tagout procedures. Following these steps will keep accidents from occurring while maintaining or repairing machinery. Keep in mind that any time a worker chooses, he or she may apply additional measures or apply a lock or tag to any or all of the electrical isolating devices.

Let's review the nine steps:

Think, plan and check. Think through the entire procedure and identify all parts of any systems that need to be shutdown.
Communicate. Let other employees working on the equipment know when and why you are shutting down the system.
Locate all power sources. Locate all switches and other electrical sources that need to be locked out.
Neutralize all power at its sources. Lower any suspended parts and block any moveable parts and disconnect the electricity.
Lockout all power sources. Used a lock designed for only this purpose and a lockout tag that includes your name, and the time, the date and department.
Test operating controls. Test the operating controls to make certain the power has been removed.
Turn the controls back off. Be sure to check each and every control is in the "OFF" position before beginning any necessary maintenance or repairs.
Perform any maintenance or repairs.
Remove locks and restore energy.

Tools should be removed from equipment and machine guards put back in place. Notify other workers that the machines are working and back on. Restart equipment only after all workers are at a safe distance.

Rates & Calculations

This section of the Fundamentals of Electricity program will equip you with the knowledge to calculate the energy use and energy costs associated with any piece of electrical equipment, and will provide you with a full review of the various components typically found on a monthly electric bill.

You'll also learn how to calculate the more fundamental aspects of single-phase and three-phase power - including voltage, current, impedance, wattage, and amperage - using key axioms such as Ohm's Law and Watts Law.

And finally, you'll learn the basic principles and formulas for calculating power factor and voltage drops.

Ohm's Law
Watt's Law
Voltage Drop

Voltage Drop
Calculating Energy Use & Costs
Calculating Electric Bills

Ohm's Law

The electrical relationship between voltage, current, and impedance is called Ohm's law. Ohm's law is a simple mathematical formula which says the voltage in a circuit can be computed by multiplying the current flowing in the circuit times the impedance of the circuit. The "impedance" of a circuit is measured in ohms and is represented by the letter Z. The term impedance is used to include both inductive and capacitive reactance and resistance because all three are forms of opposition to the flow of current.

Ohm's Law is written as V = A x Z where

V = voltage (volts)
A = current (amps)
Z = impedance (ohms)

The electrical impedance of a circuit is made up of both the electrical resistance and the electrical reactance of the elements in the circuit. Both the resistance and reactance impede the current flow through a circuit.

Resistance loads include incandescent light bulbs and electric heating elements. Reactive loads include electric motors and other devices where the magnetic field created around a coil of wire or in a capacitor is utilized as electrical energy.

Resistive Loads Reactive Loads Combination Loads

Resistive Loads

In AC and DC circuits containing purely resistive loads, like lights and heaters, Ohm's Law can be used to compute current, voltage and resistance in the circuit.

In a resistive DC circuit, both current and voltage are fixed, steady values.

In an AC resistive circuit, the current alternates exactly in step with the voltage. In either case, Ohms Law can be applied.

In a resistive circuit Ohm's Law states that: voltage is equal to current times resistance.

Ohm's Law V = A x R where:

V = voltage (volts)
A = current (amps)
R = resistance (ohms)

For example, a current of 2 amps flowing through a resistance of 3 ohms is said to produce a voltage "across" that resistance of 6 volts.

A simple diagram shows the relationship between all three values. Current will be equal to voltage divided by resistance, and resistance is equivalent to voltage divided by current.

Example:
A wire with a resistance of 10 ohm's is connected to a 9-volt battery. To determine the current flow in the wire, use ohm's law and divide 9 volts by 10 ohm's. The current flow in the wire equals 0.9 amps. Replace the 9-volt battery with a 1.5 volt battery. Using the same wire the calculated current flow is 1.5 volts divided by 10 ohms, which produces a current flow of 0.15 amps. The larger voltage results in more pressure to force more current through the given resistance of 10 ohms.

Reactive Loads

The current and voltage in AC circuits that contain inductors, capacitors, or both, behave much differently than in a purely resistive circuit. We cannot measure resistance directly in these circuits. We measure what's known as "reactance."

Inductors and capacitors react to current flow in ways that oppose, or impede, changes in the flow of current, but they do it in a different fashion than a pure resistor. Each device has its own characteristics which creates an impeding force.

Whenever there is an inductor, or coil, in a circuit, we call its impeding force to current flow "inductive reactance." For a circuit with a capacitor, the impeding force is called "capacitive reactance."

We treat both resistance and reactance as impedance, that is, any opposition to changes in the flow of current.

Inductive Reactance Capacitive Reactance

Capacitive Reactance

A capacitor is a device that is able to store electrical energy. We talk in terms of a capacitor being "charged up," or building a "voltage potential," when current flows through the device.

A capacitor is comprised of two or more electrically conductive surfaces called "plates," insulated from each other by a material called a dielectric. Materials such as air, paper, mica and oil can be used as dielectrics.

In the very first instant that current flows, there is a surge of electrons to one plate. They are following the natural laws of attraction. Once this plate becomes saturated, the plate is fully charged.

The amount of charging a capacitor can achieve is called capacitance and is measured in Farads, or microfarads, µF.

The opposition to the flow of alternating current due to capacitance is called "capacitive reactance." It is measured in ohms just like resistance and inductive reactance.

In capacitors, the current leads voltage by 90 degrees.

The formula for calculating the Capacitive Reactance, or impedance of a capacitor is:

Capacitive reactance, denoted as x sub c (X_C), is equal to the constant one million (or 106) divided by the product of 2^p( or 6.28) times frequency times the capacitance .

where:

X_C = Capacitive reactance measured in ohms.
f = is the AC frequency in Hertz.
C = is the capacitance in microfarads.

Example:
A capacitor with a capacitance of 106.1 microfarads is connected to a 120 volt, 60 hertz AC circuit. To determine the current flow in the wire, first find the capacitive reactance of the capacitor. The capacitive reactance equals 1,000,000 divided by 6.28 times 60 hertz times 106.1 microfarads which equals 25 ohms. Now use ohm's law and divide 120 volts by 25 ohms which equals 4.8 amps.

Remember the current will lead the voltage by 90 degrees so the current flow is 90 degrees ahead of the voltage sine wave.

Combinations-Resistive & Reactive

A resistive circuit opposes current directly. A reactive circuit transforms current and creates opposition to current flow in the process. For example, when current flows through an inductor, each winding creates an electromagnetic field. These electromagnetic fields interact with one another, creating an overall induced field that we can observe as measurable voltage. This interchange of energies between the windings of the coil creates an opposition to the flow of current called "inductive reactance."

Similarly, a capacitive circuit will create an opposition to current flow. The capacitor reacts to current flow and creates an electric field that is measurable as voltage. The resultant opposition to current flow is called "capacitive reactance."

When a circuit has a combination of these element, resistors, capacitors, and inductors, the calculation of the total impedance to current flow is calculated by the formula:

Z equals the square root of the resistance squared plus the difference of the capacitive reactance and the inductive reactance squared.

Where:

Z = total impedance in ohms
R = resistance of the circuit in ohms
XC = Capacitive reactance of circuit in ohms
XL= Inductive reactance of circuit in ohms

Example:
Find the current flowing to an electric motor operated at 240 volts that has an electrical resistance of 80 ohms, an inductive reactance from the motor windings of 90 ohms, and a capacitive reactance from a connected capacitor of 30 ohms. You cannot find the total impedance by adding the resistance and reactance together since they are not in phase. Use the equation for calculating the total impedance. The square root of 80 squared + ( 30 squared - 90 squared equals a total impedance of 100 ohms. Use ohms law to find the current flow by dividing 240 volts by 100 ohms and the current flow equals 2.4 amps.

Watt's Law

Single Phase Three Phase Power Factor

Single Phase

A watt is the unit of measure used to express electrical power, generation and use. We choose light bulbs based on wattage. The greater the wattage, the higher the amount of power consumed to produce light.

In a single-phase AC circuit like the one in our homes, the relationship between wattage, voltage, and current is known as Watt's Law, and is stated as :

Watt's Law: W = V x A x p.f.

wattage equals voltage times current times power factor.

Where:

W = wattage (watts)
V = voltage (volts)
A = current (amps)
p.f. = power factor

For resistive loads: p.f. = 1.0
For inductive/Capacitive Loads: p.f. < 1.0

For purely resistive loads, such as heaters, or light bulbs, the power factor equals 1.0. For inductive or capacitive loads like motors, the power factor is less than 1.0 and must be determined by actually measuring it or from the nameplate of the device.

Knowing Watt's Law is very helpful when troubleshooting electrical systems where circuit breakers are tripping or fuses are blowing. For instance, if you were trying to run a microwave, coffee maker, toaster, and blender all at the same time and kept tripping the circuit breaker, how could you figure the total load on this circuit?

By adding the wattage of each of the loads and dividing by the circuit voltage, an approximation of the current flowing through the circuit could be found. Comparing this value to the rating on the circuit breaker would determine whether the circuit breaker is functioning properly. If the calculated current was less than the circuit breaker rating, then there is a problem in that circuit.

Watt's Law - Three Phase

Three phase power is used primarily in commercial and industrial environments, providing power to motors and equipment. It is more economical to operate large equipment with three phase power. In order to calculate three-phase wattage, we multiply the average voltage of each phase times the average current of each phase, times the power factor, then multiply by the square root of 3. The square root of 3 is equal to 1.732, so the equation is written as shown:

Watt's Law: W = V avg. x A avg x p.f. x 1.732

Where:

W = wattage (watts)
V_avg = average voltage of the three separate phases (volts)
A_avg= average current of the three separate phases current (amps)
p.f. = average power factor or the three separate phases
1.732 = a constant necessary with 3 phase.

In a three phase circuit, the use of the constant 1.732 results from the fact that not all three phases are producing the same amount of power at the same time. Each phase's voltage and current move through zero at different times. Suffice it to say that the correct power from a three-phase system at any point in time is found by multiplying by the square root of 3.

The electrical power input in kilowatts for a three phase motor is calculated by multiplying the average voltage of all three phases measured at the motor times the average amperage of all three phases measured at the motor times the average power factor of all three phases measured at the motor times a constant of 1.732 and dividing the result by 1000.

An operating three phase motor has voltages measured with a voltmeter on each phase of 453, 458, and 461 volts, amperage measured on each phase with an ammeter are 14.1, 13.9, and 13.8 amps, power factor was measured as 0.82. The average voltage is 453 plus 458 plus 461 divided by 3 which equals 457 volts.

The average current is 14.1 plus 13.9 plus 13.8 divided by 3 which equals 13.9 amps.

The electrical power input to the motor equals 457 volts times 13.9 amps times 0.82 power factor divided by 1000 which equals 5.2 kilowatts.

(457V x 13.9A x .082pf x 1.732) / 1000 = 9.02 Kwatts

Power Factor

Power factor is a comparison of the power used by the load, called "real power," divided by the power supplied to the load, which is called "apparent power." The difference between the real power and the apparent power is called "reactive power." Reactive power performs no useful work but it must be supplied to the customer in order for motors and other inductive loads to operate.

Power factor is essentially the ratio of the useful work performed by an electrical circuit compared to the maximum useful work that could have been performed at the supplied voltage and amperage. Low power factors can be a problem for some customers because their electrical distribution system may not have adequate current-carrying capacity. In fact, customers frequently run out of distribution capacity because they didn't consider power factor into their original circuit design. In addition, some utilities have significant economic penalties for low power factors.

Resistive loads, like light bulbs and heaters, have power factors of 1.0 which is called the "ideal" power factor. Inductive loads like motors have power factors of less than 1.0, usually between 0.5 and 0.95, depending on their size and how they are operated.

Power factor is expressed as the ratio of real power to apparent power, as shown by the equation: power factor equals real power divided by apparent power

Where:

Power Factor = given as a decimal or a percentage.
Real Power = measured in units of watts or kilowatts.
Apparent Power = measured in units of volt-amps or thousands of volt amps, kVA.

Real power is measured by a wattmeter, and apparent power is measured by a voltmeter and ammeter. Power factor is important because the power supplier must supply both real and reactive power to meet the customers needs. Customers are sometimes only billed based on the real power they use. Standard utility meters measure real power and cannot measure reactive power without special modifications. A low power factor is generally considered to be anything less than an 80 to 90 percent power factor rating.

Voltage Drop - Definition

Wires carrying current always have inherent resistance, or impedance, to current flow. Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance.

A common analogy used to explain voltage, current and voltage drop is a garden hose. Voltage is analogous to the water pressure supplied to the hose. Current is analogous to the water flowing through the hose. And the inherent resistance of the hose is determined by the type and size of the hose - just like the type and size of an electrical wire determines its resistance.

Excessive voltage drop in a circuit can cause lights to flicker or burn dimly, heaters to heat poorly, and motors to run hotter than normal and burn out. This condition causes the load to work harder with less voltage pushing the current.

The National Electrical Code recommends limiting the voltage drop from the breaker box to the farthest outlet for power, heating, or lighting to 3 percent of the circuit voltage. This is done by selecting the right size of wire and is covered in more detail under "Voltage Drop Tables."

If the circuit voltage is 115 volts, then 3 percent of 115 volts is 3.5 volts. This means that voltage lost from the wires in the circuit should not exceed 3.5 volts and the outlet should still have 115 - 3.5 or 111.5 volts to supply. Since most appliances require an extension cord to plug into an outlet, some voltage drop will occur in the extension cord as well. Some motors will not run correctly, and could even burn up, if the voltage at the motor falls too low.

Causes	Formulas
Measurement	Voltage Flicker

Tables

Causes

Voltage drop is caused by resistance in the conductor or connections leading to the electrical load. There are many causes of resistance in the conductor path. There are four fundamental causes of voltage drop:

1. Material - Copper is a better conductor than aluminum and will have less voltage drop than aluminum for a given length and wire size.

2. Wire Size - Larger wire sizes (diameter) will have less voltage drop than smaller wire sizes (diameters) of the same length.

3. Wire Length - Shorter wires will have less voltage drop than longer wires for the same wire size (diameter).

4. Current Being Carried - Voltage drop increases on a wire with an increase in the current flowing through the wire.

Voltage Drop Limits
The National Electric Code, Section 210-19(a), recommends limiting the voltage drop to 3% on a branch circuit to the farthest output for power, heating or lighting. The fine-print note to NEC Section 215-2(b) recommends limiting voltage drop on feeder conductors and the branch circuit to the farthest outlet should not exceed 5%.

Measuring Voltage Drop

Voltage drop under typical operating conditions can easily be measured. If excessive voltage drop is suspected in a circuit, follow these steps:

1. Turn on all the electrical equipment which is normally in operation at the time excessive voltage drop is suspected to be a problem.

2. Measure the voltage at the service panel that supplies the circuit in question. It should be 234 volts or more between hot conductors and 117 volts or more between hot and neutral of a 120/240 volt, single phase system (maximum of 3% voltage drop on service drop). If not, call the utility.

3. Measure the voltage at the service panel board with the problem circuit. It should be 227 volts or more between hot conductors and 113.5 volts or more between hot and neutral of a 120/240-volt, single phase system (maximum of 3% voltage drop on feeders, 2% maximum recommended).

4. Measure the voltage at the problem piece of equipment. It should be 220 volts or greater between hot conductors of a 240-volt circuit or 110 volts or greater between hot and neutral of a 120-volt circuit (maximum of 3% voltage drop on the branch circuit back to the service panel board).

Results
If a problem with the voltage exists at the main service - call the utility .

If voltage at main service was fine but low at service panel - check feeder from main service for problems.

If voltage at service panel was fine but low at outlet or controller, check branch circuit for problems.

Remember
A 480 volt circuit should be a minimum of 480 volts at the transformer secondary and a minimum of 440 at the equipment outlet or controller.

A 240 volt circuit should be a minimum of 240 volts at the transformer secondary and a minimum of 220 at the equipment outlet or controller.

A 120 volt circuit should be a minimum of 120 volts at the transformer

secondary and a minimum of 110 at the equipment outlet or controller.

Voltage Drop Formulas

The size of conductor for any voltage drop can be determined readily by using mathematical formulas which calculate the voltage drop for given wires sizes, lengths, and types under load. These formulas may be used to determine any one of the four factors affecting voltage drop if the other three factors are known. Keep in mind there are separate formulas for single and three phase, and for copper and aluminum.

Formulas

For Copper Single Phase Circuits:

Where:

CM = Area of conductor in circular mills
1 = Single Phase line current in Amperes
L = Length (one-way) of circuit in feet
V = Voltage Drop (Volts)

For Copper Three Phase Circuits:

Where 13 = average three phase line current in amperes.

For sizes of aluminum conductors, these formulas may be used and the results multiplied by 1.6 or the formulas may be modified as follows:

Find the size of copper wire to carry a load of 40 amperes at 240 volts a distance of 500 feet with 2% voltage drop. Use the formula:

Example 1
Referring to Table showing "Data on Sizes & Weights of Conductors," it will be found that this size lies between No. 1 and No. 0, so No. 0 would be the wire size selected. For aluminum, multiply 104,167 x 1.6 = 166,667 circular mils. This lies between No. 00 and No. 000, so No. 000 would be selected.

Example 2
How far can No. 6 copper wire be used to carry a load of 30 amperes at 240 volts and keep within 1% voltage drop?

Voltage Flicker

Starting motors under high loads also causes voltage drop which is often evidenced by flickering lights. Such voltage drop associated with motors is called voltage flicker.

This flicker is objectionable only when the magnitude and frequency of occurrence of the voltage drop exceed certain thresholds. The threshold of objection is shown on a Voltage-Flicker curve. If the magnitude of the voltage drop and the frequency of occurrence lie below the threshold of perception, people generally do not notice any flicker.

Voltage Drop Tables

A number of electrical reference books contain voltage drop tables which allow the correct wire size to be determined if the desired voltage drop limit, maximum current, and distance from the source to the load are known. These tables are very convenient and do not require the use of the mathematical formulas. They do require you to find the appropriate voltage, phase, conductor material, and voltage drop table in order to determine the correct answer. This requires a large number of tables.

To use the tables, find the amperage in the left column and the length of run or distance between the source and load along the top of the table. If your number is between two of the table numbers, use the higher value. The row and column where they intersect on the table is the recommended wire size that will keep voltage drop within acceptable limits.

Using Voltage Drop Tables

* Wire Type: There are different tables for Copper and Aluminum wire.

+ Amperage: The maximum amperage this table can be used for.

D Voltage: The voltage rating for this table. There are different tables for each of the standard service voltages.

O Phase: There are different tables for Single and Three Phase power.

l Percent Voltage Drop: The allowable voltage drop limits for table. There are tables with other values.

Minimum Size of Conductor: * Copper, + Up to 200 Amperes, D 115-120 Volts, 0 Single Phase, l Based on 3% Voltage Drop

Length of Run in Feet

In Air Cable or Conduits

Example:
Find the size of copper wire to carry a load of 40 amperes at 120 volts a distance of 500 feet with 3% voltage drop. Use the Table: Note the column heading of the table: Copper, Single Phase, 120 volts, 3% voltage drop. Follow the first column "amperage" down to 40 amps. Find the 500 feet column in the table under length of run. Where the 40 amp row and 500 foot column cross, the wire size can be found. In this case, a 00 or 2 ought copper wire. This method of finding the correct wire size is simple when you have the right table.

Length of Run in Feet

Compare Size Below With Size Left Of Double Line And Use Largest Size

50	75	100	125	150	175	200	225	250	275	300	350	400	450	500	550	600	650	700

14	14	14	14	12	12	12	10	10	10	10	8	8	8	8	8	6	6	6
14	14	12	12	12	12	10	10	8	8	8	8	6	6	6	6	6	4	4
14	12	12	10	10	8	8	8	8	8	6	6	6	4	4	4	4	4	3
12	10	10	8	8	8	6	6	6	6	4	4	4	4	3	3	2	2	2
12	10	8	8	6	6	6	4	4	4	4	3	3	2	2	2	1	1	0

10	8	8	6	6	6	4	4	4	4	3	2	2	1	1	1	0	0	0
10	8	6	6	4	4	4	4	3	3	2	2	1	1	0	0	00	00	00
8	8	6	6	4	4	3	3	2	2	2	1	0	0	0	00	00	000	000
8	6	6	4	4	3	3	2	2	2	1	0	0	0	00	00	000	000	4/0
8	6	4	4	4	3	2	2	1	1	1	0	00	00	000	000	000	4/0	4/0
8	6	4	4	3	2	2	1	1	1	0	0	00	000	000	000	4/0	4/0	250

6	4	4	3	2	2	1	1	0	0	00	00	000	000	4/0	4/0	250	250	300
6	4	3	2	2	1	0	0	0	00	00	000	4/0	4/0	250	250	300	300	300
6	4	3	2	1	0	0	00	00	00	000	4/0	4/0	250	250	300	300	350	350
4	4	2	1	1	0	00	00	000	000	000	4/0	250	250	300	300	350	400	400
4	3	2	1	0	0	00	000	000	000	4/0	250	250	300	350	350	400	400	500

4	3	1	0	0	00	000	000	4/0	4/0	4/0	250	300	350	350	400	500	500	500
4	2	1	0	00	000	000	4/0	4/0	250	250	300	350	400	400	500	500	600	600
3	1	0	00	000	000	4/0	4/0	250	250	300	350	400	500	500	500	600	600	700
2	1	0	00	000	4/0	250	250	300	300	350	400	500	500	600	600	700	700	750
2	0	00	000	4/0	250	250	300	350	350	400	500	500	600	700	700	750	800	900

Procedure: Find the amperage in the left column and the length of run along the top of the table (if between two of the table values go to the higher value). Where the two intersect on the table is the recommended wire size that will keep voltage drop within acceptable limits. Compare the recommended value on the right side of the table to the value shown on left side (minimum NEC requirements for the insulation type to be used) and use the larger size.

In Air Cable or Conduit




				Direct	Burial	Overhead	In Air
Load in Amps	UF	RH, THW, NM, RHW, THWN, USE, SE	THHN	UF	USE	Single	Triplex
5	14	14	14	14	14	10	8
7	14	14	14	14	14	10	8
10	14	14	14	14	14	10	8
15	14	14	14	14	14	10	8
20	12	12	12	12	12	10	8

25	10	10	10	10	10	10	8
30	10	10	10	10	10	10	8
35	8	8	8	8	8	8	8
40	8	8	8	8	8	8	8
45	6	8	8	6	8	8	8
50	6	8	8	6	8	8	6

60	4	6	6	4	6	8	6
70	4	4	6	4	4	6	6
80	3	4	4	3	4	6	4
90	2	3	4	2	3	4	4
100	1	3	3	1	3	4	4

115	1/0	2	2	1/0	2	3	3
130	2/0	1	2	2/0	1	2	2
150	3/0	1/0	1	3/0	1/0	1	1
175	4/0	2/0	4/0	2/0	1/0	1/0	1/0
200		3/0	3/0		3/0	2/0	2/0

Calculating Energy Use & Cost

Fuel Cost/Fuel Adjustment
kWh Use	kW Use

Fuel Cost Adjustment/Fuel Charge - How To

You can calculate the cost of energy use for various electrical appliances and equipment if you have these three pieces of information:

§ the rated power of the appliance, usually given in watts;

§ the length of operating time,

§ and the cost of electricity.

The rated power, in kilowatts, is multiplied by the operating hours to determine the energy use in kilowatt hours. The energy use is then multiplied by the electric rate to determine the cost of electricity to run the appliance.

For example, let's determine the cost to run a 1,500-watt heater for six hours based on an electricity cost of eight cents per kilowatt hour.

The power rating of the heater is 1,500 watts. To convert this to kilowatts, divide 1,500 watts by 1,000. This yields 1.5 kilowatts. Now multiply the power use, 1.5 kilowatts, by the operating time of 6 hours; which equals 9 kilowatt-hours of energy use. Finally, multiply the 9 kilowatt hours of energy use times the electric rate of eight cents per kilowatt-hour. You now know it costs 72 cents the operate the heater for 6 hours.

On larger appliances, like refrigerators and water heaters, there is a yellow label on the side which states how much energy costs to run the appliance for a year. If you look closely you can see that the manufacturer has used "averages," family size, hours per day, etc, to determine the annual operating costs for this appliance.

Energy Use = Power x Time

kWh = kW x Hours

then:

Operating Cost ($) = Energy Use (kWh) x Electric Rate

Calculating Energy Use & Cost - kWh Use

While electrical power measured in kilowatts is important to the people who design and size the electrical system, most consumers are more interested in the amount of electrical energy that is used in their house, or by a single appliance. The term used in measuring electrical energy is the "kilowatt-hour." This is a measure of the amount of electrical power used in one hour. Kilowatt-hours are what the electric meter on the side of your house measures. This is the basis for calculating your monthly electric bill.

Once you know the energy use of any appliance, you can figure the cost to run that appliance. There are three methods of finding the amount of electrical energy being used by a piece of equipment.

They are:

1. estimating wattage and time;
2. using the kilowatt-hour meter;
3. and installing a check meter.

Estimating
Meter-Disk Revolutions

Using Check Meter
Reading kWh Meter

Determining kWh Use - Estimating

To estimate the energy use of a piece of equipment, take the power use, in watts, from the nameplate, divide by one-thousand, and multiply the result times the estimated operation time, in hours. This is especially helpful when a rough estimate of consumption is needed.

For example: How much energy does a refrigerator use per day? The refrigerator’s nameplate says it is rated at 1200 watts. We estimate that it runs about 20 percent of the time.

Dividing 1200 watts by 1000 gives us 1.2 kilowatts of power use. Take 20 percent of 24 hours a day, which equals 4.8 hours. The daily energy use is found by multiplying 1.2 kilowatts times 4.8 hours which equals 5.76 kilowatt-hours of energy use. The annual energy use for this refrigerator is 5.76 kilowatt hours per/day times 365 days per year, or about 2100 kilowatt hours a year.

Determining kWh Use - Meter-Disk Revolutions

You can also count the meter-disk revolutions on the kilowatt-hour meter to determine the watt-hour consumption of an appliance, just as you can count meter revolutions to determine the kilowatt consumption of an appliance. This is a method of making a quick, accurate check of equipment already in use.

Each meter has a flat aluminum disk with a black mark along its edge. This disk turns when energy is being used. Meters also have a meter constant. The constant is shown on the meter nameplate. A constant "Kh = 7.2" means that for each revolution of the disk, 7.2 Watt-hours has been used (constants will vary with different meters).

To determine how much electrical energy is used by counting meter-disk revolutions, proceed as follows:

1. Find the circuit that supplies the appliance you wish to check, for example, a portable heater. Plug the portable heater into the outlet where the appliance is to be checked, then remove the fuses at the fuse box or trip the circuit breakers until the heater goes off. Replace the fuse or return the circuit breaker to the "on" position. This fuse or circuit breaker serves the circuit you want to check. Remove all other fuses, or trip all other circuit breakers, so that all other circuits are off.

2. Disconnect any other equipment on the same circuit with the appliance to be checked, or make sure that switches are in the "off" position so that all other appliances which are on the same circuit have been disconnected.

3. With a watch, check the number of meter-disk revolutions over a timed period. You may use any period of time. Six minutes makes a good period for equipment that operates continuously. Six minutes is one-tenth of an hour and can be easily calculated. Equipment, such as a refrigerator, that is off part of the time should be checked through at least one "on-and-off" cycle.

4. Determine watt-hours of energy used in the timed period by multiplying the meter constant by the disk revolutions for that period. We will assume the meter constant to be 7.2 (Kh = 7.2).

5. Divide the minutes in the timed period into 60 minutes to determine how many such periods there are in an hour. The six-minute period used will equal 10 periods in an hour. If the check period is 15 minutes, there will be four periods in an hour.

6. Multiply the number of watt-hours you measured in step four by the number of time periods per hour. This will give the total number of watt-hours of energy used per hour.

7. Determine the number of hours equipment is used per month. For equipment that is connected to the circuit continuously, you figure the total hours per month (24 hrs. x 30 days = 720 hrs. per month). For equipment that is used only part of the time, such as a heater, toaster or iron, estimate the number of hours used per month. For this problem, assume that the heater operates for an average of two hours each day.

8. Multiply hours of operation per month by watt-hours used per hour to determine the number of watt-hours used per month.

9. Divide watt-hours used per month by 1,000 to find number of kilowatt-hours used per month. Then multiply the number of kilowatt-hours by the per kWh cost charged by the utility to determine to cost to operate that appliance for that length of time.

Determining kWh Use - Using A Check-Meter

A check-meter is a regular kilowatt-hour meter installed to measure electrical usage of one particular piece of equipment. Power suppliers or equipment dealers sometimes supply them where there are questions or considerable interest in how much electricity a specific piece of equipment uses. The check meter may be used over a period of several days, months, or years. This provides a precise measure of the number of kilowatt-hours used during a given measuring period.

1. Note and record the meter reading at the beginning of the check period.
2. Determine the length of time needed between meter readings to gain the desired information.
3. Note and record the meter reading at the end of the check period.
4. Calculate total kilowatt-hours of energy used by subtracting the beginning reading from the final reading.

Determining kWh Use - How To Read kWh Meter

Reading an electric meter is actually quite simple to do, once you understand how. Many customers like to read their own meters throughout the month to gauge how much electricity they are using. Most new kilowatt-hour meters have cyclometer dials, that contain numbers like your car’s mileage odometer. These are easy to read. Here are instructions for reading an older style kilowatt-hour meter with pointers on the dials.

Notice that some of the dial hands on the meter turn clockwise and some turn counter-clockwise. Look at the first dial on the right. It’s turning clockwise and the hand is between the 7 and the 8. You want to record the number that the hand just passed, in this case, 7.

The second dial is turning counter-clockwise and is just past the 3, so that's the number you write down and so on.

Now, if the hand is directly on a number, you read it differently. Look at the dial to the right of the dial you are reading. If the hand on the right has passed zero, write down the number the hand on the left is pointing to, in this case, the 7. If the hand on the right is not past zero, then write down the next lowest number on the dial you're reading.

Take a look at these dials and see if you can get a reading - it's a little tougher (show meter on screen). What did you get? 8737 is correct.

Now, if you read this meter at the same time yesterday, you would subtract yesterday's reading from today's reading to determine the number of kilowatt-hours used in one day.

To calculate the cost of the energy use, multiply the number of kilowatt-hours by the cost per kilowatt-hour. The section "Calculating Electric Bills" provides additional detail on electric prices and specific electric bill components you should be aware of.

Calculating Electric Bills

Rates/Prices Bill Components Power Factor

Electric Rates/Prices

Electric rates, the cost of energy per kilowatt-hour, vary from utility to utility; by rate class within a utility, and sometimes even by the time of day or the season of the year. Each power supplier has established rate schedules that are usually approved by regulatory agencies for a given customer type.

The base electric rate is applied to the number of kilowatt-hours consumed during a billing period, approximately a month long, to determine the electric bill. The billing period will usually not be the same as the calendar month and the meter may run 30 to 32 day intervals - and not on exactly the same day of each month.

Other charges may be added to the base cost of electricity. These may include a charge for minimum monthly service, demand charges on larger customer accounts, fuel adjustment charges, other surcharges, power factor penalties and taxes. Rates charged in the summer months may differ from those charged during the winter. Special rates may be offered for customers who agree to let the power supplier cycle equipment on and off such as electric heaters or air conditioners during high use times of the day or year. All of these charges and their application are covered under "Electric Bill Components."

Estimated Rate Actual Rate

Estimated Rate

An estimate of the electric rate can be made by looking at the most recent electric bill.

1. First, find the dollar amount and the kilowatt-hours used.
2. Then divide the dollar amount by the total number of kilowatt-hours used.
3. The result is an estimated average rate for the last billing period.

This same method can be used to find an average yearly estimate of the electric rate by adding the dollar amounts of all the bills during the last year and dividing by the total kilowatt hour usage of all the bills during the last year.

Actual Rate

The actual electrical rate is determined by finding the appropriate rate class for the customer and using the rate schedule for that rate class. The rate schedule provides the necessary information to determine all of the components which make up the rate. Rate schedules are available from the utility.

Rate Classes Rate Schedules

Rate Classes

In general, there are three common rate classifications in the electric utility industry: residential, small general service and large general service. There may also be commercial and industrial classes. Each of these rate classes may have many subclasses according to size of electrical service required or other variations. In addition, special incentive rates may apply to any of the rate classes.

Some utilities may offer special categories of rates for operations such as irrigation or street lighting. The residential rate is used to supply lighting, heating, and small motors in residences, on farms, or in small shops. Small general service or commercial rates are generally used for commercial operations like professional offices, retail establishments, institutional facilities and restaurants. Demand or large general service rates generally apply to large processing and manufacturing operations, universities and hospitals.

Each rate class may be further subdivided into different categories based on the amount of power the customers use.

Rate Schedule

The rate schedule or tariff, as it is sometimes referred to, lists the various types and amounts of charges that can be made to customers in a particular rate category. These various types of charges include the customer charge, the rate for energy and how it is structured, the demand charge and how it is determined, any charges or penalties for low power factor, and other charges as approved by the governing regulatory agencies.

Rates within some schedules change for certain periods of the day, or season of the year. Some rate schedules charge a high cost for the first several hundred kilowatt hours of use each month, and lower costs for each subsequent block of kilowatt hours. Some rate schedules have separate fuel cost adjustments to reflect the actual cost of fuels used to make the power or the costs incurred to purchase power from another company when needed. Others have special demand charges and some include special economic incentives.

Electric Bill Components

Customer Charge
The customer charge is generally the base monthly charge the customer pays regardless if they use any power or not. This base charge covers things like the cost of meter reading, billing and accounting.

Energy Rate
The energy rate is the rate paid for each kilowatt-hour of energy used by the customer. The energy rate might be structured in many varying ways. Some utilities use a flat energy rate. This means the customer pays the same for the first kilowatt-hour as the last kilowatt-hour they use. This makes calculating the energy rate fairly simple since the energy rate does not change.

Some utilities use block rates where the cost per kilowatt hour varies based on the amount of energy the customer uses. In a block rate, the first block - for example the first 500 kilowatt-hours of energy used by the customer - is the most expensive and charged at the highest rate. The next block of energy used - say the next 1000 kilowatt-hours - is charged at a medium rate. Any energy use greater than the first two blocks, or 1500 kilowatt-hours, is charged at the lowest rate. The size and number of blocks can vary greatly from utility to utility.

Block rates have fallen out of favor with regulatory agencies because of the belief that these rates encourage the waste of electricity by promoting the attitude: "The more I use the cheaper it gets."

Fuel Charge Demand Rate Power Factor Penalty

Electric Bill Components

Fuel Cost Adjustment/Fuel Charge

A fuel cost adjustment can be found on most bills from electric utilities. Since most utilities must file the rates they are going to charge with regulatory agencies, they have to project the amount and cost of fuel they'll use to produce electricity and the amount and cost of any purchased power they project they'll need to buy. In performing these projections, the estimates may be higher or lower than the actual costs. So the actual cost of fuel and purchased power incurred is compared to the projected costs the rates were based on. The difference - "or adjustment charge" is then multiplied by the kilowatt-hours of energy used to account for any changes in fuel and purchased power prices.

Electric Bill Components - Demand Rate

Demand rates or demand charges as they are often called are applied on certain rate schedules, most commonly the large general service or industrial class. These rates are based on the peak demand or highest amount of power in kilowatts the customer used during the billing period. This is done because some customers require rather large amounts of power for short periods of time. This high short term power use requires larger transformers, power lines, and generating capacity to meet these infrequent peak needs. Demand rates were designed to allocate the costs of building and maintaining the electrical system for the peak periods to serve the customers who require that capacity.

There are a number of ways the demand or peak power is determined. The most common method is to measure the highest average power use in kilowatts during a 15 or 30 minute period each month. This peak power or peak demand is multiplied times the unit charge, usually in dollars per kilowatt to determine the demand charge listed on the bill. The demand charge is added to the customer charge, energy charge, and fuel cost adjustment, and any taxes to arrive at the total bill.

Demand rates are also financial incentives for commercial and industrial customers to pay attention to their power use patterns. Some demand rates are based on the highest demand for power measured the previous 12 months, called a ratchet.

Consider this example where the highest peak demand measured on the customer's service in the last 12 months was 350 kilowatts and occurred 8 months ago. If this utility had a demand ratchet, the customer would be billed for the 350 kilowatts worth of peak power usage each following month regardless of the actual demand used as long as it's less than 350 kilowatts. As soon as the customer reaches a new peak demand higher than 350 kilowatts, they are billed for that amount of demand charge for the next 12 months or until they use more and set a new higher peak.

Electric Bill Components - Power Factor Penalty

An electric rate may also include additional charges when the customer has a power factor less than some preset limit, typically between 80 and 90 percent. This is called a power factor penalty since it is a penalty assessed on the customers electrical bill for lower than optimum power factor. Special devices called capacitors can be installed by either the utility or the customer to improve a poor power factor. The power factor penalty is an incentive for the customer to pay attention to the power factor at their operation and consider installation of power factor correction capacitors rather than pay a penalty. Power factor correction can be tricky to calculate. Always refer to the appropriate electric rate tariff sheet and have the calculations checked by a professional.

The power factor penalty is commonly structured as an additional demand charge. If the normal demand charge was $5 per kW per month, the power factor penalty might add $2 additional per kW per month to the charge for a total of $7 per kW per month. This extra amount would be the penalty paid because of the low power factor.

Power Factor

Power factor is expressed as the ratio of real power to apparent power, as shown by the equation: power factor equals real power divided by apparent power

Where:

Power Factor = given as a decimal or a percentage.
Real Power = measured in units of watts or kilowatts.
Apparent Power = measured in units of volt-amps or thousands of volt amps, kVA.

Generation Overview

alt="Simple Hydro-Electric Graphic" v:shapes="_x0000_s1104">The generation of electricity is most commonly achieved by convertingchemical energy in fuels or the flowing energy of wind, water, or steam intoelectrical energy, using a mechanical turbine connected to a generator. The force of the fluid causes the turbine to rotate, which in turn rotates the magnetic field inside the generator to produce electricity.

First, let's take a quick look at how this happens in a typical power plant. Then we'll explore each part of the process in more detail. And finally, we'll review how electric utilities manage and dispatch the power from their generating plants to meet customers' needs.

Typically, a fuel such as coal or oil is burned in a boiler to produce steam. The chemical energy in the fuel becomes heat energy as it burns, forming hot gases. To help protect the environment, these gases are cleaned by special equipment before they are released through the stack.

The steam, under great pressure, rushes through pipes and valves and turns the steam turbine at high speed. The turbine is made up of blades on a shaft and is driven by the steam like wind drives a windmill. Heat energy in the steam is converted to mechanical energy by the turbine.

When the steam leaves the turbine it goes to the condenser. Water from a nearby source is used in the condenser to cool the steam back to water. The water is sent back to boiler to become steam again.

The rotor in the generator is turned by the shaft from the turbine and electricity is produced. The mechanical energy produced in the turbine is changed to electrical energy in the generator.

Steam Turbines

Steam Turbine Power Generating Plant Picture

A steam turbine power generating plant is the most common type of power plant today. This type of plant converts heat into electricity usually using a boiler, and a turbine to drive an electric generator. Large-scale commercial size systems use steam produced from a variety of sources including nuclear reactions, burning fossil fuels and wastes, and even geothermal energy. The most common fuels used at steam turbine plants to produce steam are coal, oil, and natural gas.

The steam boiler is essentially a large tea kettle and the steam turbine acts much like a windmill to turn the generator to make electricity.

After the steam passes through the turbine, it is condensed back into water and pumped back into the boiler to be reheated into steam again. This condenser usually uses cool water from a lake, river, or bay or may use a large cooling tower.

Gas Turbines

Gas turbines are very similar to jet engines in design, except that they include extra blades -- called the power turbine -- on a shaft connected to a generator. It is relatively simple way to generate electricity with a minimum of equipment, but the efficiency of conversion is so low that it is seldom used except for times of intermittent use.

The gas turbine's biggest advantage is that it can be started and produce electricity significantly faster than a steam turbine. This rapid response makes it an attractive source for providing capacity during periods of peak electrical generating requirements. Gas turbines are also much smaller and less expensive than their steam turbine counterparts which makes them easier to transport and install on short notice.

Co-Generation

Co-generation is defined as the co-production of power and useful heat when fuel is burned in a power generation cycle. Using the excess or waste heat to provide some economic benefit such as process heat or water heating can make compelling economic sense. It has been used for decades in large pulp and paper, chemical, petroleum, and other heat-intensive processing industries.

Cogeneration lends itself to a natural partnership between utilities and large industrial customers, particularly when the utility is installing new generating plants anyway. Large industrial customers can often use the waste heat from the utility's power generating cycles for industrial processes. Likewise, when a large industrial customer becomes a cogenerator, the customer may agree to sell its excess power generation -- if there is any -- to the utility.

There are three basic cogeneration designs in common use: steam turbines, internal combustion engines, and gas turbines. In each case, the engine is used to produce power and the waste heat is captured to provide process heating.

Combined-Cycle

Combined cycle generators use a combination steam turbine/gas turbine configuration to generate electricity. Gas turbine exhaust can be used to generate steam which in turn can be used to make even more power in a steam turbine. This combined cycle process achieves a very high efficiency in the conversion fuel energy to power.

When a dependable and reasonably priced supply of natural gas and/or good quality fuel oil is available, combined cycle can be used for base-load power generation, especially where some or all of the steam leaving the steam turbine can be used by an industrial process.

Photovoltaic Cells

Photovoltaic or solar cells (PV for short) are made of silicon and can turn sunlight directly into DC electricity. Each cell produces a small amount of current. By connecting many cells together and placing them on larger panels, the electric current produced can be significant. This can be used directly in a DC appliance, stored in batteries, or converted to AC to operate AC appliances using an inverter.

alt="PV Panels Picture 2" v:shapes="_x0000_s1110">While extremely simple, photovoltaic cells are expensive compared to other generating sources. While the cells themselves are fairly reliable, the sun's rays are not a very predictable resource in most areas. Therefore, other equipment such as battery storage systems and an inverter to convert the DC current AC are often needed. Solar or PV power has consequently mostly been used for specialized situations such as satellites, portable electronic equipment such as calculators, and power in remote locations. Less than 1 percent of the nation's electricity is produced using PV cells.

Coal

Coal is an abundant and relatively inexpensive fuel on a dollar per BTU basis in North America. Fifty-five percent of the United States' utilities' net electric generation comes from coal. However, coal fired power plants are more complicated, largely due to the coal handling equipment and strict environmental regulations, and are generally more expensive to build than oil or natural gas fired plants.

The coal is most often delivered to the power plant using railroad cars or barges and stored on a stock pile which usually contains a 90-day supply. The coal is transported from the storage pile to the plant where it is ground into a fine powder and burned in the boiler.

Coal presents several environmental challenges in that it produces more combustion byproducts than either oil or gas. Burning coal produces four main byproducts which must be carefully controlled in compliance with strict federal and regulations. These include fly ash, bottom ash, nitrogen oxides, and sulfur oxides. Many utilities sell fly ash to concrete companies to be used as a concrete additive. Bottom ash is collected and stored until it can be ground up and used as a concrete additive and for stabilizing road beds. Scrubbers and other equipment are used to clean and limit the amount of sulfur oxides and nitrogen oxides released through the stack.

Environmental emissions are also affected by the type of coal which is burned. Three different types of coal are burned in North America -- anthracite, bituminous, and lignite -- and they are generally considered to be high-, medium- and low-quality coal, respectively. The higher the quality of coal, the higher the heating value and the lower the sulfur and ash content per pound. These characteristics help to improve fuel efficiency and reduce environmental emissions.

Nuclear

Nuclear power plants were once thought to produce the least expensive power, even cheaper than hydroelectric plants. Today, they have proven to be more "risky" due to high costs of construction and operation, concerns over nuclear waste disposal, and the general uncertainty surrounding the deregulation of the electric utility industry. In fact, no new reactors have been ordered in the United States since 1978. Yet, nuclear power is still a significant source of electricity for us, accounting for 22 percent of utilities' net power generation in the United States.

Nuclear powered steam generating plants are similar to fossil fired plants in that they use steam to drive a turbine and generator to make electricity. In a nuclear powered steam generating plant, heat is produced to boil water into steam from the slow, controlled nuclear reaction known as "fission", or splitting of atoms.

The reactor is comprised of a core containing nuclear fuel, water, control rods, and an enclosed steel container called a reactor vessel. As the control rods are lifted out of the core containing the nuclear material, the nuclear reaction begins and heat is produced.

There are two distinct types of nuclear plants: boiling water and pressurized water reactor designs. The boiling water reactor is the older design where the heat produced from the nuclear reaction boils water in the reactor vessel itself. Steam is then piped directly to the turbine that drives the generator to produce electricity.

The newer design employed by most nuclear power plants in the U.S. is called a pressurized water reactor. The heat generated by the nuclear reaction in a pressurized water reactor is absorbed and carried to the steam generator by water under very high pressure which is then used to produce steam.

Natural Gas

Natural gas is often used in the southern and western U.S. states where supplies are plentiful and the distance from the well-head source is relatively small. Natural gas is delivered to the plant through large gas lines buried underground and on-site storage is not common.

For some, natural gas is a preferred fuel source due to the relatively cheap boiler designs required to burn it and inexpensive operating and maintenance costs. However, price fluctuations and supply uncertainties make it unpopular in many electric utility planning circles. The decade following the oil embargoes of the 1970's prohibited the use of natural gas for electricity generation, but those laws were revoked in 1987. Today, natural gas accounts for 10 percent of utilities' net generation in the United States.

Oil

Oil was the primary fuel source of older steam generating plants. These plants were designed to burn heavier grades of oil rather than lighter weight heating oils, although they can use either type. Before the early and mid 1970s oil embargoes, oil was plentiful and cheap. After the crisis, oil prices skyrocketed and using oil to generate electricity became extremely expensive. Today, only two percent of the United States' utility net generation comes from oil-fired plants.

Oil-Fired Steam Generating Plant Graphic

Oil-fired steam generating plants are relatively simple. Oil is stored in large storage tanks and pumped through delivery lines into the boiler. The amount or flow of oil is controlled by valves which can increase or decrease the flow of oil depending on the amount of steam needed to generate electricity. The turbine, generator, and condenser are similar to those in other types of steam generating plants.

Oil is also burned as a backup fuel at natural gas and coal-fired steam generating plants. These plants maintain a backup supply of oil since it can be stored in large storage tanks for extended periods. Should the supply of natural gas or coal be interrupted, the plant operators switch to burning oil to make steam. This explains why it is common to see oil storage tanks at natural gas and coal power plants.

Waste

Wood waste from furniture manufactures, old tires, and even solid municipal and waste can all be used as a fuel source to produce steam. Many cities and towns have looked to this method because of their need for electricity and their growing concerns over landfill capacity. But, these plants have proved to be fairly expensive to operate due to high maintenance costs. In addition, the ash from the burned waste can at times become a hazardous waste, increasing the disposal cost to significant levels compared to a normal landfill.

Landfill Gas

Solid waste in landfills produces methane, the major constituent in natural gas. When landfills reach capacity, they are typically sealed and covered with layers of dirt. The biological process of decomposition produces a low of grade methane gas. It is possible to "mine" this gas, drill a well and collect it for use as a fuel to generate electricity using an internal combustion engine modified for this purpose or burned in a boiler to make steam. One drawback to this type of system is the quality of gas produced. It is typically very low grade methane gas and contains many compounds and pollutants which must be "scrubbed" or removed from the gas before being burned in an engine. These compounds will cause significant degradation or damage to the engine in a short amount of time if they are not removed.

Generation Dispatch

Electricity is unique in that it must be produced the instant it is needed. It just cannot be economically stored in large quantities using today's technology. And, unlike telephone service, power users do not tolerate a busy signal.

The utility normally tries to schedule and operate a series of generators at a given power level known to be the most efficient for the season and time. As the customers' needs for power change, the dispatchers must adjust the amount of electricity produced by various generation units. If the required load is higher than what the generators are currently producing, the system's electrical frequency falls below the desired value of 60 cycles. The generation dispatchers decide which unit is the most economical to increase power output, or they bring an additional generating unit on line to raise the frequency back up to 60 cycles. If the generators are producing too much electricity compared to what the required load is, the system frequency increases above 60 cycles and the generation dispatchers decide which unit's power generation needs to be lowered.

In the event the electric utility doesn't generate the required power when it is needed, the system voltage drops below the minimum setpoint, and circuit breakers begin to trip to prevent equipment damage. This can cause major power outages for consumers. Fortunately, today's electric utilities have interchange agreements with other power suppliers that minimize the likelihood of this happening.

Electric utilities also plan their power generation to meet widely varying demands during the year, and during any given day. Because of the varied schedules on which customers use electricity, the load varies over the day, the week, and the year. Normally, the load tends to be lowest at night, when most people are asleep, and highest during the day, when the most appliances are in use. Some utilities see a peak at night due to electric space heating in the colder months, while most utilities see a peak during the hottest days of the summer when air conditioners are working their hardest.

When a utility has its highest demand for power in the winter, it is referred to as winter peaking. When the demand for power is highest in the summer, it is called summer peaking. Some utilities have such dramatic load growth that they have both.

More Information

Load Factor
Dispatch Criteria
Load Management

Load Factor

A utility's load factor is its average load as a percentage of its peak load. Think of it in terms of an airplane flying without all of its seats full. If the utility distributes power to a dedicated transformer at a customer's facility which has a 100-seat capacity and can fly 365 days a year, but only has 50 percent of its seats full, the customer's load factor is 50 percent. Large industrial customers can have load factors of more than 90 percent and customers such as convention centers can have load factors of under 10 percent. It is much more expensive to serve the customers with low load factors. The more high load factor customers a utility has, the higher the utility's own load factor will be. In this business, the higher the load factor, the better.

More Information

Base Load
Intermediate Load
Peak Load

Peak Load

The peak demand periods are relatively infrequent occurrences, and may even be met by neighboring electric utility company's generating units. Peak demands are important to a utility since they dictate the maximum amount of power the utility must generate or buy from somewhere else in order to meet the needs of the entire electrical system. There are daily, seasonal, and annual peak loads that all require careful generation planning.

Intermediate Load

Intermediate plants generally have their power output increased every morning and throughout the day, and then decreased every evening. They run considerably more hours than peaking units, but fewer than base-load units. Utilities typically meet intermediate loads with older generating units that were once base-load plants, but have now been replaced by newer, more efficient units for base-load service.

Comments

UnknownOctober 13, 2010 at 3:52 PM
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UnknownOctober 13, 2010 at 3:53 PM
its a good blog..i found useful information here..if anybody want more information about this den visit http://www.tycoproducts.co.uk/

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