ECS Electrical Supply Systems and Distribution 1

Question 1

What is the standard nominal voltage for a single-phase domestic supply in the United States?

Accepted Answer

120V

Answer

The standard nominal voltage for a single-phase domestic supply in the US is 120V (nominally, though it may vary slightly between 114V and 126V).

Question 2

In a three-phase electrical supply system, what is the phase angle between each of the three phases?

Accepted Answer

120 degrees

Answer

In a balanced three-phase system, each phase is displaced by 120 degrees from the others, equally dividing the 360-degree cycle.

Question 3

What type of transformer connection is most commonly used to supply three-phase power to commercial buildings in the US?

Accepted Answer

Delta-Wye

Answer

A Delta-Wye (Delta-Star) transformer configuration is most commonly used to step down transmission voltage for commercial distribution, providing both line-to-line and line-to-neutral voltages.

Question 4

What is the primary purpose of a main distribution board (MDB) in an electrical installation?

Accepted Answer

To distribute power to sub-circuits and provide overcurrent protection

Answer

A main distribution board distributes incoming electrical power to multiple outgoing circuits while housing protective devices such as circuit breakers and fuses.

Question 5

Which of the following best describes a 'radial circuit' in electrical distribution?

Accepted Answer

A circuit where power flows in one direction from the supply to the final outlet

Answer

A radial circuit runs from the distribution board in one direction to supply outlets or loads, with the cable terminating at the last point without returning to the board.

ECS - Electrotechnical Certification Scheme Practice Test

ECS - Electrotechnical Certification Scheme Practice Test

ECS Electrical Supply Systems and Distribution 1