ECS Electrical Supply Systems and Distribution 3

Question 1

What is the maximum permitted voltage drop from the supply terminals to any point in a final circuit for lighting loads under NEC guidelines?

Accepted Answer

3%

Answer

1%

Answer

5%

Answer

10%

Question 2

In electrical distribution, what is meant by 'prospective short circuit current' (PSCC) at a given point?

Accepted Answer

The maximum current that would flow if a zero-impedance short circuit occurred at that point

Answer

The current that flows during normal operating conditions

Answer

The current required to operate protective devices during a fault

Answer

The current drawn by all connected loads at maximum demand

Question 3

What is the purpose of power factor correction capacitors in an electrical distribution system?

Accepted Answer

To reduce reactive power and improve the power factor of the supply

Answer

To increase the voltage available to connected loads

Answer

To protect against voltage surges from the utility

Answer

To balance unequal loads across three phases

Question 4

Which instrument would an electrician use to measure the impedance of an earth fault loop at a point in an installation?

Accepted Answer

An earth fault loop impedance tester

Answer

A multimeter set to resistance

Answer

A power quality analyser

Answer

An insulation resistance tester

Question 5

What is the significance of the 'short circuit capacity' (SCC) rating marked on a circuit breaker?

Accepted Answer

The maximum fault current the breaker can safely interrupt without damage

Answer

The maximum load current the breaker can carry continuously

Answer

The voltage rating above which the breaker will not operate

Answer

The minimum current required to trip the breaker

Question 6

In a three-phase balanced load, if the line current is 20A, what is the total three-phase apparent power (VA) supplied at 208V line-to-line voltage?

Accepted Answer

7,205 VA

Answer

4,160 VA

Answer

12,470 VA

Answer

3,606 VA

Question 7

What is the primary reason for balancing loads across the three phases of a three-phase distribution system?

Accepted Answer

To minimize neutral current and prevent overheating of the neutral conductor

Answer

To increase the supply voltage available to loads

Answer

To allow higher voltage loads to be connected

Answer

To reduce the number of protective devices required