NEC Quiz: Article 430 Answers, Part 4

by Mark Lamendola

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  1. The motor branch-circuit short-circuit and ground-fault protective device muste be capable of carrying the starting current of the motor [430.52(C)].

  2. You could replace that motor with a non wound-rotor motor, which per Table 430.52 can be protected by a 300A inverse time breaker. You could replace the 150A inverse time breaker with an 800A instantaneous trip breaker per this table, but it probably still would not start. You could try adjusting the inverse time breaker, if possible. Or, per Exception 1 of 430.52(C) you can use the next size up. And if none of these remedies are practical or effective, you have four remedies available in Exception 2 of 430.52(C). If none of those work, you either have a load problem or you have the wrong motor for the application.

  3. It must be adjustable and part of a listed combination motor controller having coordinated motor overload. It must also have short-circuit and ground-fault protection in each conductor and the setting must be adjusted to no more than the value specified in Table 430.52 [430.52(C)(3)]. Also, it cannot be used on circuits with more than one motor or with a motor and any other load; in those applications, you can use only fuses or inverse time circuit breakers [430.53].
  4. The correct answer is C. C. The branch circuit must be protected by a fuse or breaker with a rating that does not exceed that specified in 430.52 for the highest rated motor plus an amount equal to the sum of the Full Load Current (FLC ) ratings of all other motors and the ratings of other loads connected to the circuit [430.53(C)(4)].
  5. To size the overcurrent protection device (OCPD) for a torque motor circuit, use the nameplate current rating per 240.4(B) [430.58 and 430.52(D)].