E2 Sizing and Protection of Motor Circuits 4

Question 1

Per NEC Table 430.52, the maximum rating of an inverse time circuit breaker for a Design B, squirrel cage motor branch circuit is:

Accepted Answer

250% of FLA

Answer

Table 430.52 allows a maximum inverse time circuit breaker rating of 250% of the motor's FLA for Design B squirrel cage motors.

Question 2

Per NEC Table 430.52, the maximum rating for a non-time-delay fuse used for branch-circuit short-circuit protection of a Design B squirrel cage motor is:

Accepted Answer

300% of FLA

Answer

Table 430.52 permits non-time-delay fuses rated up to 300% of the motor's FLA for branch-circuit short-circuit and ground-fault protection.

Question 3

Per NEC Table 430.52, the maximum dual element (time-delay) fuse rating for a Design B squirrel cage motor is:

Accepted Answer

175% of FLA

Answer

Dual element time-delay fuses are limited to 175% of the motor FLA for Design B motors under Table 430.52.

Question 4

Per NEC 430.52(C)(2), if the maximum standard inverse time breaker size cannot carry the motor's starting current, the breaker rating may be increased to a maximum of:

Accepted Answer

400% of FLA

Answer

NEC 430.52(C)(2) allows the inverse time breaker to be increased to a maximum of 400% of FLA when the standard 250% cannot handle motor starting current.

Question 5

Per NEC 430.110(A), the ampere rating of the motor circuit disconnecting means must be at least what percentage of the motor's full-load current rating?

Accepted Answer

115%

Answer

NEC 430.110(A) requires the motor disconnecting means to have an ampere rating of at least 115% of the motor's full-load current rating.

(E2) E2 Commercial Electrical Inspector Practice Test

(E2) E2 Commercial Electrical Inspector Practice Test

E2 Sizing and Protection of Motor Circuits 4