AC Systems Lesson 4

Conductor resistance causes a(n) ? between the voltage source and the connected

load.

a.

decrease in current

b.

power loss

c.

voltage drop

d.

all of the above

The NEC recommends that voltage drops on branch circuits not exceeding ? at the

farthest outlet of power, for heating or lighting loads, will provide for reasonable

efficiency of operation.

a.

2%

b.

3%

c.

4%

d.

5%

Loads are normally connected in ? with the source, and the resistance of the line is in

? with the source.

a.

parallel / parallel

b.

parallel / series

c.

series / parallel

d.

series / series

If a generator voltage is 240 volts, and the load voltage is 235 volts, how much voltage

is dropped on the line?

Answer:

What is the percentage of voltage drop if you have 235 volts at a load fed from a 240-

volt source? (Round the FINAL answer to one decimal place.)

Answer:

%

Two rows of fluorescent lamps are installed in an office on the same branch circuit, with

each row drawing 12.5 amperes. The source voltage is 277 volts, and the total line

resistance of the circuit conductors is 0.5 Ω. The wire used has a constant (k) of 12.6.

What is the voltage at the load? (Round the FINAL answer to one decimal place.)

Answer:

Two rows of fluorescent lamps are installed in an office on the same branch circuit, with

each row drawing 12.5 amperes. The source voltage is 277 volts, and the total line

resistance of the circuit conductors is 0.5 Ω. The wire used has a constant (k) of 12.6.

What is the percentage of voltage drop? (Round the FINAL answer to one decimal place.)

Answer:

%

Two rows of fluorescent lamps are installed in an office on the same branch circuit, with

each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance

is 0.5 Ω. The wire used has a constant (k) of 12.6. The voltage drop will be within the

recommendation of the NEC.

Select one:

True

False

How could you correct a voltage drop problem involving two rows of fluorescent fixtures

fed from the same circuit in a practical manner?

I. Change the fluorescent fixtures to incandescent light fixtures.

II. Install a lighting panel closer to the fixtures.

III. Install larger wire.

IV. Put each row of fixtures on a separate circuit.

a.

I. or II.

b.

I. or III.

c.

II. or III.

d.

III. or IV.

Two rows of fluorescent lamps are installed in an office on the same branch circuit, with

each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance

is 0.5 Ω. The wire used has a constant (k) of 12.6. If the load is 129 feet from the source,

what is the specific wire size used in this installation? (Assume 75°C wire.)

Wire size = ____ AWG

Answer:

Two rows of fluorescent lamps are installed in an office on the same branch circuit, with

each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance

is 0.5 Ω. The wire used has a constant (k) of 12.6. If the load is 130 feet from the source,

what size wire would you need to install for this circuit to meet the recommendations of

the NEC for acceptable voltage drop on a branch circuit? (Assume 75°C wire)

Wire size = ____ AWG

Answer:

A motor was overheating because of low voltage at its terminals. A transformer was

installed to correct the problem. What is the secondary voltage of the transformer

required to be in order to supply 240 volts to the motor? (Round the FINAL answer to one

decimal place.)

Answer:

Use the diagram to determine total resistance. (Round the FINAL answer to one decimal

place.) Note: Use the rated voltage and wattage to determine resistance.

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine total current. (Round the FINAL answer to one decimal

place.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the voltage drop of the conductors. (Round the FINAL

answer to two decimal places.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the voltage at the load after calculating the voltage drop

of the wire.

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

a.

115.34 V

b.

117.67 V

c.

120 V

d.

122.33 V

Use the diagram to determine the power loss in the conductors. (Round the FINAL

answer to two decimal places.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the current of the motor. (Round the FINAL answer to two

decimal places.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the current of each 100 W lamp. (Round the FINAL answer

to three decimal places.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the current of the 75 W lamp. (Round the FINAL answer to

three decimal places.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the total current of the loads. (Round the FINAL answer to

one decimal place.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

In a parallel circuit, the total current equals the sum of the current of the loads.

Select one:

True

False

Use the diagram to determine the total power consumed by the circuit.

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the power consumed by the motor. (Round the FINAL

answer to one decimal place.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the power consumed by each of the 100 W lamps. (Round

the FINAL answer to the nearest whole number.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the power consumed by the 75 W lamp. (Round the FINAL

answer to one decimal place.)

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

Use the diagram to determine the power consumed by the loads.

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Answer:

The total power consumed by the circuit is equal to the power consumed by the loads.

Note: Ra and Rb represent the resistance of the wire. The 120 volts of the motor and

lamps is their rated voltage and not the actual voltage.

Select one:

True

False

Use the diagram to determine the voltage across the load when the push button is

depressed. (Round the FINAL answer to one decimal place.)

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

What would the current flow be if a short circuit is put across the battery's terminals?

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

How much power is consumed by the load under short-circuit conditions?

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

When the battery terminals are open, how much power is consumed by the load?

Answer:

Use the diagram to determine the power consumed by the motor when the push button

is depressed. (Round the FINAL answer to the nearest whole number.)

Answer:

Use the diagram to determine the power consumed by the motor when the push button

is depressed. (Round the FINAL answer to the nearest whole number.)

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

Use the diagram to determine the power consumed by the motor when the push button

is depressed. (Round the FINAL answer to the nearest whole number.)

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

Use the diagram to determine the power consumed by the motor when the push button

is depressed. (Round the FINAL answer to the nearest whole number.)

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

Use the diagram to determine the power consumed by the motor when the push button

is depressed. (Round the FINAL answer to one decimal place.)

Note: All voltage sources contain internal resistance that is usually ignored in

calculations because the resistive value of the load is so much greater than the

resistance of the source. This is not always the case. (Rb represents the battery's internal

resistance.)

Answer:

What is the value of RL when the wattage is at peak?

a.

0.01 Ω

b.

0.25 Ω

c.

0.05 Ω

d.

1.00 Ω

Use the diagram to determine the voltage drop across the resistor R. (Round the FINAL

answer to two decimal places.)

Answer:

Use the diagram to determine the voltage drop across load M. (Round the FINAL answer

to two decimal places.)

Answer:

Use the diagram to determine the voltage drop across load L. (Round the FINAL answer

to two decimal places.)

Answer: