NECA Electrical Systems & Equipment 2

Question 1

What is the maximum voltage drop allowed by the NEC for branch circuits as a recommendation?

Accepted Answer

3%

Answer

The NEC recommends a maximum 3% voltage drop on branch circuits for optimal efficiency.

Question 2

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

Accepted Answer

Delta-Wye

Answer

Delta-Wye transformers are standard for commercial applications because the Wye secondary provides a neutral for 120V single-phase loads.

Question 3

A 480V, 3-phase motor draws 40A at full load. What is the approximate kVA demand?

Accepted Answer

33.3 kVA

Answer

kVA = V × A × √3 / 1000 = 480 × 40 × 1.732 / 1000 ≈ 33.3 kVA.

Question 4

Which device automatically disconnects a circuit when it detects an arc fault condition?

Accepted Answer

AFCI breaker

Answer

An Arc Fault Circuit Interrupter (AFCI) detects dangerous arc faults and opens the circuit to prevent fires.

Question 5

What does the 'interrupting rating' of a circuit breaker indicate?

Accepted Answer

Maximum fault current it can safely clear

Answer

The interrupting rating specifies the maximum short-circuit current the breaker can safely interrupt without damage.

(NECA) National Electrical Contractors Association Practice Test