NECA Electrical Systems & Equipment 2 — Questions and Answers
Question 1: What is the maximum voltage drop allowed by the NEC for branch circuits as a recommendation?
- 3% (Correct answer)
- 5%
- 10%
- 2%
Correct answer: 3%
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?
- Delta-Wye (Correct answer)
- Wye-Delta
- Delta-Delta
- Wye-Wye
Correct answer: Delta-Wye
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?
- 33.3 kVA (Correct answer)
- 19.2 kVA
- 57.6 kVA
- 9.6 kVA
Correct answer: 33.3 kVA
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?
- AFCI breaker (Correct answer)
- GFCI receptacle
- Surge protector
- Thermal relay
Correct answer: AFCI breaker
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?
- Maximum fault current it can safely clear (Correct answer)
- Continuous current it can carry
- Voltage rating of the breaker
- Trip time at 150% overload
Correct answer: Maximum fault current it can safely clear
The interrupting rating specifies the maximum short-circuit current the breaker can safely interrupt without damage.
Question 6: In an electrical panel, what is the purpose of a main bonding jumper?
- Connects the neutral bar to the equipment grounding conductor (Correct answer)
- Provides surge protection
- Limits current to branch circuits
- Isolates the neutral from ground in sub-panels
Correct answer: Connects the neutral bar to the equipment grounding conductor
The main bonding jumper connects the grounded (neutral) conductor to the equipment grounding conductor and enclosure at the service entrance.
Question 7: What is the standard frequency of alternating current in the United States?
- 60 Hz (Correct answer)
- 50 Hz
- 400 Hz
- 25 Hz
Correct answer: 60 Hz
The US uses 60 Hz AC power, while most of Europe and Asia use 50 Hz.
NECA Electrical Systems & Equipment 2
What is the maximum voltage drop allowed by the NEC for branch circuits as a recommendation?