E2 Sizing and Protection of Motor Circuits 2

Question 1

Per NEC 430.22, the minimum ampacity for branch circuit conductors supplying a single continuous-duty motor shall be what percentage of the motor's full-load current?

Accepted Answer

125% of FLA

Answer

NEC 430.22 requires branch circuit conductor ampacity of at least 125% of the motor's FLA for continuous-duty applications.

Question 2

Which NEC table provides full-load current values for single-phase AC motors used for conductor and protection sizing?

Accepted Answer

Table 430.248

Answer

Table 430.248 lists FLA values for single-phase AC motors, which are used in place of nameplate values for conductor and overcurrent device sizing.

Question 3

A 5 HP, 230V, single-phase motor has a table FLA of 28A. What is the minimum required branch circuit conductor ampacity?

Accepted Answer

35A

Answer

Minimum conductor ampacity = 125% × FLA = 1.25 × 28A = 35A per NEC 430.22.

Question 4

Per NEC 430.6(A)(1), which current value is used for sizing motor branch circuit conductors and short-circuit/ground-fault protective devices?

Accepted Answer

Values from Tables 430.247 through 430.250

Answer

NEC 430.6(A)(1) requires using table values from 430.247–430.250, not the motor nameplate, for conductor and short-circuit/ground-fault protection sizing.

Question 5

A 20 HP, 460V, 3-phase motor has a table FLA of 27A. What is the minimum branch circuit conductor ampacity required by NEC 430.22?

Accepted Answer

33.75A

Answer

125% of 27A = 33.75A is the minimum conductor ampacity per NEC 430.22 for continuous-duty operation.

(E2) E2 Commercial Electrical Inspector Practice Test

(E2) E2 Commercial Electrical Inspector Practice Test

E2 Sizing and Protection of Motor Circuits 2