CEP CEP Power Systems & Distribution 1 — Questions and Answers
Question 1: In a 3-phase, 4-wire wye system operating at 208/120V, what is the voltage measured between any two hot legs?
- 120V
- 208V (Correct answer)
- 240V
- 277V
Correct answer: 208V
In a 208/120V wye system, line-to-line voltage equals phase voltage multiplied by √3, so 120 × 1.732 ≈ 208V.
Question 2: A distribution transformer rated 75 kVA at 480V–208/120V is loaded to 80% of capacity. What is the approximate load in amperes on the secondary 208V side?
- 180A
- 208A (Correct answer)
- 240A
- 277A
Correct answer: 208A
Full-load secondary amps = 75,000 / (208 × √3) ≈ 208A; at 80% load that equals approximately 166A, closest to 180A — at full load it is 208A.
Question 3: What is the primary purpose of a distribution panel's main bonding jumper in a service entrance?
- To limit short-circuit current
- To connect the neutral (grounded) conductor to the equipment grounding system (Correct answer)
- To provide surge protection
- To balance the load across phases
Correct answer: To connect the neutral (grounded) conductor to the equipment grounding system
The main bonding jumper connects the grounded (neutral) conductor to the equipment grounding conductor and the enclosure at the service, establishing the ground reference.
Question 4: When sizing a feeder for a 3-phase motor load, the continuous load must be multiplied by what factor per NEC 215.2?
- 100%
- 115%
- 125% (Correct answer)
- 150%
Correct answer: 125%
NEC 215.2(A)(1) requires that feeders supplying continuous loads be sized at 125% of the continuous load ampere rating.
Question 5: A high-leg delta (wild leg) service has three phases. Which color identifies the high leg per NEC 230.56?
- Blue
- Orange (Correct answer)
- Yellow
- Red
Correct answer: Orange
NEC 230.56 and 408.3(F) require that the high leg (approximately 208V to neutral) of a 4-wire delta system be identified with orange color.
Question 6: In power distribution, what does the term 'demand factor' refer to?
- The ratio of maximum demand to the total connected load (Correct answer)
- The efficiency rating of a transformer
- The power factor of the overall system
- The ratio of reactive to real power
Correct answer: The ratio of maximum demand to the total connected load
Demand factor is the ratio of the maximum demand of a system to the total connected load, used to size feeders and transformers more efficiently.
CEP CEP Power Systems & Distribution 1
In a 3-phase, 4-wire wye system operating at 208/120V, what is the voltage measured between any two hot legs?