Electrical Systems Design & Installation Flashcards

A 480V, 3-phase welding receptacle circuit requires protection. Per NEC 630.11, how is the supply conductor ampacity determined for arc welders?

Answer: Based on duty cycle using Table 630.11(A)

NEC 630.11(A) requires arc welder supply conductor ampacity to be determined by multiplying the rated primary current by the duty cycle factor from Table 630.11(A).

When designing a hazardous location classified as Class I, Division 1, which wiring method is NOT permitted per NEC 501.10(A)?

Answer: Liquidtight flexible nonmetallic conduit

Liquidtight flexible nonmetallic conduit (LFNC) is not permitted in Class I, Division 1 locations; only explosion-proof fittings and approved methods like threaded RMC, IMC, or Type MI cable are allowed.

For a 3-phase, 480V motor with a nameplate FLA of 60A, what is the maximum rating of an inverse time circuit breaker permitted as the motor branch circuit short-circuit and ground-fault protection per NEC Table 430.52?

Answer: 180A

Per NEC Table 430.52, inverse time breakers for motors are permitted at 250% of FLC; for a 60A motor: 60A × 250% = 150A, but the next standard size up is permitted if 150A won't hold during starting, maximum 400% for some motor types. Standard inverse time = 250% = 150A.

What does the NEC require as the minimum number of 20A small appliance branch circuits for a residential kitchen per NEC 210.52(B)?

Answer: Two 20A circuits

NEC 210.52(B)(1) requires a minimum of two 20A small appliance branch circuits for the kitchen receptacle outlets in a dwelling unit.

A designer specifies a bus duct (busway) system for a 2000A, 480V, 3-phase distribution. What NEC article governs busway installation?

Answer: Article 368

NEC Article 368 covers busways (bus ducts), including installation requirements, supports, overcurrent protection, and permitted uses for high-capacity distribution systems.

When a service disconnect is located remotely from the meter, what is required at the meter location per NEC 230.82?

Answer: A means to disconnect all conductors from the service entrance conductors

NEC 230.82 lists equipment permitted on the supply side of the service disconnect, and the primary requirement for remote disconnects is that a means to disconnect all conductors must be accessible.

In an electrical system design using a separately derived system (480-208Y/120V transformer), where must the system bonding jumper be installed per NEC 250.30(A)(1)?

Answer: At the transformer or at the first disconnecting means

NEC 250.30(A)(1) requires the system bonding jumper for a separately derived system to be installed at the source (transformer) or at the first disconnecting means, but not both.