Electrical System Design & Installation Flashcards

When sizing a feeder for a commercial building with a calculated load of 180 amperes, what is the minimum conductor ampacity required per NEC Article 215?

Answer: 180A

Feeder conductors must have an ampacity not less than the maximum load to be served, which is 180A per NEC 215.2(A)(1).

Which NEC article governs the installation of electrical systems in hazardous (classified) locations?

Answer: Article 500

NEC Article 500 covers hazardous (classified) locations and defines the requirements for Class I, II, and III divisions.

A 240V, single-phase motor nameplate shows 18A full-load current. What is the minimum branch circuit conductor ampacity required?

Answer: 22.5A

Per NEC 430.22, branch circuit conductors for a single motor must have an ampacity of at least 125% of the motor's full-load current: 18A × 1.25 = 22.5A.

When installing a panelboard in a bathroom of a dwelling unit, what does the NEC prohibit?

Answer: Panelboard installation entirely

NEC 240.24(E) prohibits overcurrent devices from being located in bathrooms of dwelling units, guest rooms, or guest suites.

What is the maximum voltage drop recommended by the NEC for branch circuits serving lighting and receptacle outlets in a commercial installation?

Answer: 3%

NEC 210.19(A) informational note recommends that the maximum voltage drop on branch circuits not exceed 3% for best performance.

In a 3-phase, 4-wire wye system with a measured line voltage of 208V, what is the phase voltage?

Answer: 120V

In a 208V 3-phase wye system, phase voltage equals line voltage divided by √3 (208 ÷ 1.732 ≈ 120V).

What type of grounding electrode is NOT permitted to be used as the sole grounding electrode under NEC 250.52?

Answer: A single driven rod with resistance above 25 ohms

A single rod electrode with a measured resistance above 25 ohms must be supplemented with an additional electrode per NEC 250.56.