ElectricityElectricity

Principles & ApplicationsPrinciples & ApplicationsSixth EditionSixth Edition

©2003 Glencoe/McGraw-Hill

Richard J. Fowler

Chapter 16Residential Wiring Concepts

INTRODUCTION• Equipment-grounding Conductor • Ground-Fault Circuit Interrupter • Arc-Fault Circuit Interrupter• Three-Way Lighting Circuit• Four-Way Lighting Circuit• Lighted-Handle Switches• Low-Voltage Control Circuit

Facts about Residential Wiring

• A residence uses a 120-V/240-V single-phase system.

• Hot conductors are 120 V with respect to neutral.

• Hot conductors are 240 V with respect to each other.

• Neutral conductors are either white or neutral gray.

More Facts About Residential Wiring

• White conductors may be used as hot conductors.

• A GFCI protects people from ground-fault currents.

• Equipment-grounding conductors are never fused.

• An AFCI reduces the risk of electrical fires.

The motor develops a partial short. The branch circuit breaker doesn’t trip.

No shock is received because the motor frame is grounded.

7.0 A

0.0 A

7.0 A

Ungrounded table

Grounded floor

Motor

standardreceptacle

7.5 A

0.5 A

Short

There is no circuit fault. The motor is operating normally.

The motor continues to operate with some ground-fault current.

Equipment-Grounding Conductor

Equipment-Grounding Conductor

The partially shorted motor continues to run. It doesn’t trip the branch circuit breaker.

A severe, or fatal, shock is received because the motor frame is not grounded.

Then the equipment-grounding conductor develops a broken or corroded connection.

?.? A

Motor

Short

standardreceptacle

7.5 A

7.0 A

Ungrounded table

Grounded floor

0.5A

7.0 A

Motor

GFCIreceptacle

7.0 A

7.0 A

0.0 A

Ungrounded table

Grounded floor

Ground-Fault-Circuit Interrupter

With no ground, a partial short in the motor doesn’t trip the GFCI either.

No severe shock is received because the GFCI trips at about 5 mA.

Short

A faulty equipment-grounding conductor doesn’t trip the GFCI.

0.0 A

0.0 A

Loose screw

Neutral bus

Hot bus

Arc-Fault-Circuit-InterrupterCircuit Breaker

This circuit breaker will open when an arc occurs.Click the mouse to try it.

OFF ON

Ground-Fault QuizIs an equipment-grounding conductor ever fused or switched?

Is a green conductor ever used for a neutral conductor?

Can a neutral-gray conductor be used for a neutral conductor?

Will a ground-fault current greater than 10 mA trip a circuit breaker?

Will a ground-fault current greater than 10 mA trip a GFCI?

Will a load current of 25 A trip a GFCI receptacle rated at 20 A?

No

No

Yes

No

Yes

No

Will a 10-A ground-fault current cause an AFCI circuit breaker to trip? No

Wiring a Three-Way Lighting Circuit

Connect a hot conductor to the pole (dark-colored screw).

Continue the neutral and equipment-grounding conductors.

Connect a hot conductor to the remaining pole.

Again continue the neutral and equipment-grounding conductors.

Finally, connect the light fixture to the appropriate conductors.

Ground the metal box. Connect the throws together.

Lightfixture

14-2/G 14-3/G 14-2/G

A Four-Way Lighting Circuit

N

H

The circuit is in the off position. Equipment grounding is not shown.

Flipping the 4-way switch turns the circuit on.

Flipping either 3-way switch turns the light back off.

Flipping the 4-way switch again turns the circuit back on.

Flipping the other 3-way switch turns the circuit off again.

In summary, flipping any switch at any time will reverse the condition of the circuit.

When the light is off (switch open), the switch handle is lit.

N

H

Switch

120-Vlamp

When the light is on (switch closed), the switch handle is not lit.

Lighted-Handle Switch

H

NR2R1

B2B1

3-way switchS2S1

Lighted-Handle 3-Way Switches

The light is on and the handles are not lit.

When either switch is toggled, the light goes out and both handles are lit.

N

HL

ow-v

olta

gesu

pp

ly

Low-Voltage-Controlled Light Circuit

Click the mouse and watch. A switch is rocked to off. The relay opens.The light goes out. And, the switch returns to its open position.Another switch is rocked to off. Nothing happens.Again, the switch returns to its open position.Now, a switch is rocked on. The relay closes. The light goes on.Again, the switch returns to its open position.

Switching-Circuit QuizA 3-way lighting circuit requires _____ insulated conductors between switches.

A 4-way lighting circuit requires _____ insulated conductors between switches.

A _____ colored conductor should notbe used in the return leg of a switch.

A 4-way lighting circuit providescontrol of a light from _____ locations.

The handle of a lighted-handle 3-way switch is lit when the light is _____ .

A three-terminal relay stays in the on position until the _____ is pulsed.

three

three

white

three

off

off coil

REVIEW• Equipment-Grounding Conductor • Ground-Fault Circuit Interrupter • Arc-Fault Circuit Interrupter• Three-Way Lighting Circuit• Four-Way Lighting Circuit• Lighted-Handle Switches• Low-Voltage Control Circuit