CEP Power Systems & Distribution Flashcards

In a 3-phase, 4-wire wye system operating at 208/120V, what is the voltage measured between any two hot legs?

Answer: 208V

In a 208/120V wye system, line-to-line voltage equals phase voltage multiplied by √3, so 120 × 1.732 ≈ 208V.

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?

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.

What is the primary purpose of a distribution panel's main bonding jumper in a service entrance?

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.

When sizing a feeder for a 3-phase motor load, the continuous load must be multiplied by what factor per NEC 215.2?

Answer: 125%

NEC 215.2(A)(1) requires that feeders supplying continuous loads be sized at 125% of the continuous load ampere rating.

A high-leg delta (wild leg) service has three phases. Which color identifies the high leg per NEC 230.56?

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.

In power distribution, what does the term 'demand factor' refer to?

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.