ELECTRICAL DESIGN FOR BUILDINGSELECTRICAL DESIGN FOR BUILDINGS

Electricity is another of the technical bargains we haveElectricity is another of the technical bargains we havethat adds to the luxury of life. Those of you who relishthat adds to the luxury of life. Those of you who relishcamping out soon begin to realize the value of having acamping out soon begin to realize the value of having aswitch to flip, or an instant energy source with which to switch to flip, or an instant energy source with which to prepare food.prepare food.

Think how it would be without refrigeration. The ability Think how it would be without refrigeration. The ability to to

store food and retard spoiling is another technology we store food and retard spoiling is another technology we have that works well without noticing. But let the have that works well without noticing. But let the electricity go off for a while, and see all the frozen food electricity go off for a while, and see all the frozen food you have stored in the freezer go to waste.you have stored in the freezer go to waste.

So what is electricity anyway? It’s been around So what is electricity anyway? It’s been around for a good while, and we have used it for perhaps all for a good while, and we have used it for perhaps all our life without giving it a second thought. our life without giving it a second thought.

If you met a person in deepest Africa, or South If you met a person in deepest Africa, or South America and tried to explain electricity to him, what America and tried to explain electricity to him, what would you say?would you say?How do you describe the color red to a blind person. How do you describe the color red to a blind person. All the civilized world knows WHAT electricity is, but All the civilized world knows WHAT electricity is, but few of us can actually TELL what it is.few of us can actually TELL what it is.

Take a long length of wire and wind it into a Take a long length of wire and wind it into a coil, say 8” in diameter. Make three of these and coil, say 8” in diameter. Make three of these and squash the coil to an oblong shape rather than a squash the coil to an oblong shape rather than a circle, then tie the coils together to make a three-circle, then tie the coils together to make a three-sided tube. Then insert a magnetized cylindrical sided tube. Then insert a magnetized cylindrical shaft of steel into the tube inside the coils. Support shaft of steel into the tube inside the coils. Support the mechanism so it maintains its shape, connect a the mechanism so it maintains its shape, connect a device to the magnetized shaft to make it rotate and device to the magnetized shaft to make it rotate and a high speed. The interaction between the a high speed. The interaction between the magnetized shaft (called an armature) and the coils magnetized shaft (called an armature) and the coils of wire create an electrical flux that can be measured of wire create an electrical flux that can be measured and put to use. and put to use.

Then apply about a hundred years of Then apply about a hundred years of improvements to the gadget, and we have devices we improvements to the gadget, and we have devices we call motors, generators, and dynamos. All of which call motors, generators, and dynamos. All of which either create electricity, or by use of electricity, either create electricity, or by use of electricity, produce a power in which work can be accomplished. produce a power in which work can be accomplished.

Two basic kinds of electricity exist that we Two basic kinds of electricity exist that we employ to do work. One called direct current, which employ to do work. One called direct current, which comes from a chemical reaction between two or more comes from a chemical reaction between two or more materials – a device we call a battery. And a battery materials – a device we call a battery. And a battery is the only known way we have of storing electricity, is the only known way we have of storing electricity, but unfortunately, not in strong enough quantities to but unfortunately, not in strong enough quantities to provide power for use except what is needed to provide power for use except what is needed to operate appliances. We cannot power buildings by operate appliances. We cannot power buildings by battery power. It is for that reason we do not have a battery power. It is for that reason we do not have a strong, long lasting source of power that will operate strong, long lasting source of power that will operate a motor vehicle except for very limited amounts of a motor vehicle except for very limited amounts of time. time.

The type of electricity we use in buildings is The type of electricity we use in buildings is called alternating current, which means it alternates; called alternating current, which means it alternates; the force is one way, then the opposite, and so on. It the force is one way, then the opposite, and so on. It is not a force that moves, so as they say “flow of is not a force that moves, so as they say “flow of electricity.” The power is simply there, for use by a electricity.” The power is simply there, for use by a device that uses it. If it moved, electrical power would device that uses it. If it moved, electrical power would run out of a plug onto the floor. run out of a plug onto the floor.

Alternating current electrical power is generated Alternating current electrical power is generated at a central plant by large generators that are turned at a central plant by large generators that are turned by some other source of power. In the past, that by some other source of power. In the past, that power has been by the force of water moving over a power has been by the force of water moving over a wheel to turn a turbine, then by the use of natural wheel to turn a turbine, then by the use of natural gas, and as of late, by burning coal. And now, of gas, and as of late, by burning coal. And now, of course, the process of generating power from wind course, the process of generating power from wind turbines has been perfected to the point that they turbines has been perfected to the point that they can provide a constant power source. can provide a constant power source.

There are literally thousands of processes that There are literally thousands of processes that are complex, mind boggling, and efficient that use are complex, mind boggling, and efficient that use electricity to power your television, ipod, telephone, electricity to power your television, ipod, telephone, simple lighting, highly technical lighting, imaging, simple lighting, highly technical lighting, imaging, communicating, and so on. Your heart beats right now communicating, and so on. Your heart beats right now because of an electrical flux that is created by a because of an electrical flux that is created by a chemical reaction in your body between potassium chemical reaction in your body between potassium and sodium. a special group of cells that have the and sodium. a special group of cells that have the ability to generate electrical activity on their own. ability to generate electrical activity on their own. These cells separate charged particles. A These cells separate charged particles. A spontaneous leak of certain charged particles into the spontaneous leak of certain charged particles into the cells of the heart produces electrical impulses in the cells of the heart produces electrical impulses in the pacemaker cells which spread over the heart, causing pacemaker cells which spread over the heart, causing it to contract – and it does it about seventy two times it to contract – and it does it about seventy two times every minute. every minute.

Our study of electricity will be limited to Our study of electricity will be limited to buildings, and a very basic study at that, as modern buildings, and a very basic study at that, as modern technology makes building electrical systems more technology makes building electrical systems more and more complex. So we will consider the and more complex. So we will consider the destination of power into a building, how it is destination of power into a building, how it is distributed, how it is used, and how it is controlled to distributed, how it is used, and how it is controlled to be a viable asset rather than a hazard.be a viable asset rather than a hazard.

Power to serve Lubbock comes from several Power to serve Lubbock comes from several sources. There is a plant east of town called Jones sources. There is a plant east of town called Jones station, owned by Xcel energy, a plant on the Slaton station, owned by Xcel energy, a plant on the Slaton highway owned by the City, and a large plant near highway owned by the City, and a large plant near Muleshoe that operates on coal. Muleshoe that operates on coal.

The electrical systems owned by the city of The electrical systems owned by the city of Lubbock are quite small by comparison, and a great Lubbock are quite small by comparison, and a great deal of the power it has available is purchased by the deal of the power it has available is purchased by the Xcel Energy Company. All the electricity used by Xcel Energy Company. All the electricity used by Texas Tech is furnished by the City, and all the Texas Tech is furnished by the City, and all the electricity comes directly from Xcel. electricity comes directly from Xcel.

A schematic diagram illustrates how power gets A schematic diagram illustrates how power gets from the plant to your house . . .from the plant to your house . . .

TRANSMISSION STATIONPOWER

this "secondary" powerservice may be 240 voltsor 208 volts - depending

SCHEMATIC DIAGRAMOF POWER DISTRIBUTION

on customer need

other areaspower to

other areaspower to

consumer uselower power fortransformed down toelectrical service is

electricmeter

plant - may be as highpower from generatingprimary electrical

as 250,000 volts

Voltage in an electrical system is analogous to Voltage in an electrical system is analogous to PRESSURE in a water system. It is the force in PRESSURE in a water system. It is the force in electricity that overcomes friction, and makes electricity that overcomes friction, and makes power available over a long distance. power available over a long distance.

So the voltage in the wires behind your house So the voltage in the wires behind your house may be 20 to 30 k in voltage, but it must be reduced may be 20 to 30 k in voltage, but it must be reduced to a pressure that is usable for commercial and to a pressure that is usable for commercial and residential devices. The standard power delivered residential devices. The standard power delivered to your house is probably 240 volts, and in some to your house is probably 240 volts, and in some cases may be 208 volts.cases may be 208 volts.

Generally, electricity is delivered by a set of 3 Generally, electricity is delivered by a set of 3 wires, in which two are called wires, in which two are called PHASEPHASE wires and one wires and one is called a is called a NEUTRAL.NEUTRAL. When the two phase wires and When the two phase wires and the neutral is connected to a device, it delivers 240 the neutral is connected to a device, it delivers 240 volts. But since there are devices that only require volts. But since there are devices that only require 120 volts, such as lighting, your hair dryer, 120 volts, such as lighting, your hair dryer, computer, television, or vacuum cleaner, then one computer, television, or vacuum cleaner, then one phase wire and the neutral is connected to provide phase wire and the neutral is connected to provide the 120 volts. This type of electrical system is called the 120 volts. This type of electrical system is called a SINGLE PHASE service. a SINGLE PHASE service.

But in commercial applications there is But in commercial applications there is equipment that requires even more than 240 volts, equipment that requires even more than 240 volts, such as large air conditioners, elevator motors, and such as large air conditioners, elevator motors, and commercial kitchen equipment. These are supplied commercial kitchen equipment. These are supplied by four wires in the 240 volt system to actually by four wires in the 240 volt system to actually provide about 415 volts. This system is called a provide about 415 volts. This system is called a THREE PHASE system. THREE PHASE system.

From the power source in the alley behind your From the power source in the alley behind your house, wires are connected to a cylindrical shaped house, wires are connected to a cylindrical shaped box mounted on the pole, called a transformer. The box mounted on the pole, called a transformer. The device takes the 20,000 or so volts and transforms device takes the 20,000 or so volts and transforms the power down to 240 volts. The power is then the power down to 240 volts. The power is then delivered to your house by a set of three wires, delivered to your house by a set of three wires, extending first to a meter, then to a device inside extending first to a meter, then to a device inside your house called the ELECTRICAL PANEL.your house called the ELECTRICAL PANEL.

An electrical panel is a box recessed into a wall An electrical panel is a box recessed into a wall with a protective cover, and contains a number of with a protective cover, and contains a number of devices that can distribute electricity to a variety of devices that can distribute electricity to a variety of places within your house. places within your house.

15 16

1917

2018

STANDARDELECTRICAL

PANEL7

1113

9

35

1

8

1214

10

46

2

phase line Cphase line Bphase line A

neutral

The electrical panel has two columns of The electrical panel has two columns of holes in the cover, in which protective devices holes in the cover, in which protective devices are installed within the wiring to protect against are installed within the wiring to protect against overheating. The device is primarily a switch, overheating. The device is primarily a switch, which appears like a common wall switch for which appears like a common wall switch for lighting, except it is installed sideways rather lighting, except it is installed sideways rather than vertical. than vertical.

The service wires inside the panel are The service wires inside the panel are connected to the main power source. Say for a connected to the main power source. Say for a circuit of lights, a pair of wires are connected to circuit of lights, a pair of wires are connected to the service wires, which extend to one of the the service wires, which extend to one of the slots in the panel. There, is connected a switch slots in the panel. There, is connected a switch called a circuit breaker. The wiring then extends called a circuit breaker. The wiring then extends from the breaker to the location of the lighting from the breaker to the location of the lighting outlets. Should the wires overheat for whatever outlets. Should the wires overheat for whatever reason, the circuit breaker will disconnect the reason, the circuit breaker will disconnect the electrical service before danger of fire can occur. electrical service before danger of fire can occur.

The following shows a panel with the cover The following shows a panel with the cover removed to indicate how circuits are connected. removed to indicate how circuits are connected. Notice that the slots are odd numbered on the Notice that the slots are odd numbered on the left and even numbered on the right. left and even numbered on the right.

called circuit breakers, or fusesnumbered phase slot of panel,overcurrent protection in each

required to be directly grounded to a ground wire.facilities, each outlet in addition to each circuit is some type of outlets, such as in hospitals & health care

phase line C occurs only

SCHEMATIC DIAGRAM OF THREE PHASE ELECTRICAL PANEL

3 pole outlet, 3 phase, for large 1413

415 v Delta, 360 v Wye

equipment loads like A/C unitsrequires 3 phase wires + 1 neutral 15

17

neutral toground

18

16

2 phase wires + 1 neutral240 v Delta, 208 v Wye

2 pole outlet (elec. range) requires

outlets, & small motorsas lights, conveniencecircuits to outlets such

single pole ( 120v)

each circuit not toexceed 20 amperes

neutral

phase line Aphase line Bphase line C

57

11

9

31

6

1012

8

24

in 3 phase panels

3 pole outlet, 3 phase, for large

requires 3 phase wires + 1 neutralequipment loads like A/C units

415 v Delta, 360 v Wye

2 pole outlet (elec. range) requires

outlets, & small motors

240 v Delta, 208 v Wye2 phase wires + 1 neutral

as lights, conveniencecircuits to outlets such

exceed 20 ampereseach circuit not to

single pole ( 120v)

The preceding panel shown is generally the type The preceding panel shown is generally the type used for commercial applications, but illustrated to used for commercial applications, but illustrated to show the different types of electrical outlets. show the different types of electrical outlets.

As complex as electrical design sounds, there As complex as electrical design sounds, there are actually only THREE TYPES of outlets. And in are actually only THREE TYPES of outlets. And in residential construction, mostly only two are used. residential construction, mostly only two are used.

An outlet for lights, convenience outlets, and An outlet for lights, convenience outlets, and small appliances which use only 120 volts. This small appliances which use only 120 volts. This connection requires only two wires; one NEUTRAL and connection requires only two wires; one NEUTRAL and one PHASE wire.one PHASE wire.

An outlet for clothes dryers, ranges, ovens, air An outlet for clothes dryers, ranges, ovens, air conditioning compressors, and such. Look at the plug conditioning compressors, and such. Look at the plug in device on your clothes dryer. It has three prongs, in device on your clothes dryer. It has three prongs, somewhat ominous looking, each shaped a different somewhat ominous looking, each shaped a different way, so there is only one way to connect to the wall way, so there is only one way to connect to the wall outlet. Two of these prongs are PHASE wires, and the outlet. Two of these prongs are PHASE wires, and the other is a NEUTRAL. So with this type of outlet you other is a NEUTRAL. So with this type of outlet you get 240 volts. get 240 volts.

WattsWatts in an electrical system is analogous to in an electrical system is analogous to total gallons of water in a plumbing system. Like a total gallons of water in a plumbing system. Like a sink requires 2 fixture units, a water closet requires sink requires 2 fixture units, a water closet requires 3 – each refers to a quantity of water to make the 3 – each refers to a quantity of water to make the fixture operate.fixture operate.Then consider the different wattage Then consider the different wattage of light bulbs. A 60 watt bulb burn brightly, a 100 of light bulbs. A 60 watt bulb burn brightly, a 100 watt bulb even more brightly, and a 300 watt bulb watt bulb even more brightly, and a 300 watt bulb even more. even more.

AmperageAmperage in an electrical system is analogous in an electrical system is analogous to the rate at which water is supplied in a plumbing to the rate at which water is supplied in a plumbing system, like gallons per minute. Amperage is the system, like gallons per minute. Amperage is the rate at which power is used. rate at which power is used. It is amperage within It is amperage within an electrical circuit that is dangerous to humans.an electrical circuit that is dangerous to humans. For that reason, certain rules are set by the National For that reason, certain rules are set by the National Electric Code, for the protection of you and I, as Electric Code, for the protection of you and I, as unknowing, unaware, dumb consumers – for our own unknowing, unaware, dumb consumers – for our own protection. protection.

There is a relationship between volts, watts, There is a relationship between volts, watts, and amps, which is illustrated in basic formulas. and amps, which is illustrated in basic formulas.

FORMULA NUMBER ONE:FORMULA NUMBER ONE: one phase wire, one one phase wire, one neutralneutral

AMPS = WATTS / VOLTAGE x p.f.AMPS = WATTS / VOLTAGE x p.f.In formula One, the voltage is always In formula One, the voltage is always

120.120.Power factor is considered generally in Power factor is considered generally in

outlets outlets that do not utilize electricity as that do not utilize electricity as direct heat, as direct heat, as lights do. Power factor would lights do. Power factor would be considered with be considered with motors.motors.

FORMULA NUMBER TWO:FORMULA NUMBER TWO: two phase wires, two phase wires, one neutralone neutral

AMPS = WATTS / VOLTAGE x p.f.AMPS = WATTS / VOLTAGE x p.f.In formula Two, the voltage is 240In formula Two, the voltage is 240

For the purpose of this course, simply ignore For the purpose of this course, simply ignore p.f.p.f.

The National Electric Code sets two rules for safety The National Electric Code sets two rules for safety which must be followed in designing electrical which must be followed in designing electrical systems.systems.

RULE 1:RULE 1: Lighting and Convenience Outlets shall be Lighting and Convenience Outlets shall be rated at no more than 20 amperes.rated at no more than 20 amperes.

RULE 2:RULE 2: No circuit within a system can be loaded to No circuit within a system can be loaded to more than 80 percent of its capacity.more than 80 percent of its capacity.

Certainly there are a lot more rules, but these two Certainly there are a lot more rules, but these two will suffice for the time being. will suffice for the time being.

In consideration for design – what do you actually In consideration for design – what do you actually do? Your building has a number of lighting outlets, do? Your building has a number of lighting outlets, convenience outlets, special plugs for special convenience outlets, special plugs for special things. The design is to provide a system of wiring things. The design is to provide a system of wiring and circuitry that is suitable to provide the and circuitry that is suitable to provide the necessary power to all outlets in a safe and orderly necessary power to all outlets in a safe and orderly manner, and not burn down the building. manner, and not burn down the building.

What are the types of outlets that we, the What are the types of outlets that we, the unknowing, unaware, dumb and ignorant public will unknowing, unaware, dumb and ignorant public will come in contact?come in contact?

Lights and convenience outlets.Lights and convenience outlets.

You stand on a wobbly stool in the dark, fishing You stand on a wobbly stool in the dark, fishing for a burned out bulb on the ceiling. You take it out, for a burned out bulb on the ceiling. You take it out, then with the new one you had stuck in your mouth, then with the new one you had stuck in your mouth, you reach to try and find the socket – and you do – you reach to try and find the socket – and you do – and if you didn’t remember to turn the switch to off, and if you didn’t remember to turn the switch to off, the socket actually finds you. Bet you don’t do that the socket actually finds you. Bet you don’t do that again.again.

Or more often than not, to remove the cord Or more often than not, to remove the cord from a convenience outlet, what do you do. Firmly from a convenience outlet, what do you do. Firmly grasp the plastic protective device that separates grasp the plastic protective device that separates you from the wires, and pull firmly . . . No you don’t ! you from the wires, and pull firmly . . . No you don’t ! Most folks simply grasp the wire and pull, or jerk – Most folks simply grasp the wire and pull, or jerk – and for some reason the covering on wires just isn’t and for some reason the covering on wires just isn’t made for structural resistance. made for structural resistance.

So for rule 1, just how many lights can you So for rule 1, just how many lights can you put on a circuit that is limited to 20 amperes? put on a circuit that is limited to 20 amperes? Consider Formula One:Consider Formula One:

amps = watts / volts, or since you amps = watts / volts, or since you know amps and volts . . .know amps and volts . . .

Watts = volts x amps = 120 x 20 = Watts = volts x amps = 120 x 20 = 2400 watts,2400 watts,like that would be 20 lights at 100 watts each, or like that would be 20 lights at 100 watts each, or 10 lights at 200 watts each . . .10 lights at 200 watts each . . .

but lets not forget Rule Two; 2400 watts is but lets not forget Rule Two; 2400 watts is maximum capacity, and 80% of maximum maximum capacity, and 80% of maximum capacity equalscapacity equals

.8 x 2400 = 1920 watts..8 x 2400 = 1920 watts.

Maximum load on any 20 amp circuit is 1920 Maximum load on any 20 amp circuit is 1920 watts.watts.

As for convenience outlets, the National As for convenience outlets, the National Electric Code allows a load of 180 watts per plug.Electric Code allows a load of 180 watts per plug.

So divide 1920 / 180 = 10.67 plugs per So divide 1920 / 180 = 10.67 plugs per circuit.circuit.

And since most convenience outlets are And since most convenience outlets are dual (two plugs per outlet), the maximum dual (two plugs per outlet), the maximum number of convenience outlets one can place on number of convenience outlets one can place on a 20 amp circuit is 10.67 / 2 = Five.a 20 amp circuit is 10.67 / 2 = Five.

Next we will consider formula number two Next we will consider formula number two for the second type of outlet, then formula three for the second type of outlet, then formula three for the third type of outlet, then delta and wye for the third type of outlet, then delta and wye systems, wire and conduit, and finally an systems, wire and conduit, and finally an example design for a building . . .example design for a building . . .

END OF DAY 13END OF DAY 13

inches

Allowable Ampacities of insulated conductors from 1993 edition of the NationalElectrical Code. (NEC table 3 10-16 using copper wire) Not more than 3 current

STANDARD AMPERE RATING FOR BREAKERS & FUSES

NEC 240-6 Standard Ampere Ratings For Overcurrent Protection:Fuses and Fixed Trip Circuit Breakers shall be considered 15, 20, 25,30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250,300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000,4000, 5000, and 6000 amperes.

8 50 16.51 .128

285 .630300300

475750

1250150017502000

8009001000

590625650665

490520545

500

600700

350400

380

420460

310336

.998750

1250

200017501500

1000900800

1.291.411.521.63

1.031.091.15

500400350

700600

.813

.893

.964

.681

.728

3/04/0

250

1/02/0

200230

256

150175

4321

685100115130

65

105.6133.1167.8211.6

250

.470

.528

.575

.373

.419

26.2441.7452.6266.3683.69

.232

.260

.292

.332

.184

Size ofConductor

carrying conductors in raceway.

ELECTRICAL

141210

202535

AllowableAmperage

AreaKCMIL

4.116.5310.38

.064

.081

.102

Dia.

WIRE SIZE

FOR PARALLEL CONDUCTORS CONDUCTOR

over 350 kcmil thru 600 kcmil

over 600 kcmil thru 1100 kcmil

over 1100 kcmil

2 or smaller

2/0 or 3/0

over 3/0 thru 350 kcmil

1 or 1/0

2/0

3/0

4

2

1/0

8

6

5"

97

635439

73

133

2924

161412

20

33

97

5"

67

NEC table 250-94 copper wire

GROUNDING ELECTRODE

11

10 4 6 11 19 26 43 61 95 127 163

GROUND WIRE SIZE

3

2

111

1

11

1

3/4"

SIZE OF LARGEST SERVICE ENTRANCECONDUCTOR OR EQUIVALENT AREA

400500600700750

1/2"

1/02/03/04/0

250300350

8

6

321

4 111

1

1

1 1 2 4 5 71

DIAMETER OF CONDUIT1"

1

1 11

2"

1

11

11

SIZE OF

1 21 2

3"

11

33

43

4"

3 4

44

65

3 51 2

1 1

11

111

11

11

1 3

111

221

32

54

10

3 5221

443

5

4 77 12654

1096

13

10

22

16

218 12 161412105 7

433

654

76 9

10

13

10876

98

1815

66

4836312719

17 2715139

232014

32

23

49

3647403425

85

62

108

3/4"

CONDUIT SIZE

1/2"

1412

WIRE SIZE

AWG &KCMIL

64

NEC table 3A

DIAMETER OF CONDUIT2"1"

2924

1613

4032

6553

4"3"

192157

9376

143117

16

10

6"

9

1411

49

29

232018

4135

106917857

141

6"