FREE Journeyman Electrician’s Overcurrent Protection Questions and Answers

Question 1

According to NEC 240.4(D), what is the maximum standard overcurrent protective device (OCPD) rating for 10 AWG copper conductors that are not part of a multi-outlet branch circuit supplying receptacles?

Accepted Answer

30A

Answer

NEC Section 240.4(D)(7) specifies that unless specifically permitted elsewhere in the Code, the overcurrent protection for a 10 AWG copper conductor shall not exceed 30 amperes.

Question 2

An electrician is installing a feeder tap that is 15 feet long. The feeder is protected by a 200A circuit breaker. What is the minimum required ampacity for these tap conductors?

Accepted Answer

67A

Answer

According to NEC 240.21(B)(2), for feeder taps not over 25 feet long, the tap conductors must have an ampacity of not less than one-third of the rating of the overcurrent device protecting the feeder conductors. Therefore, 200A / 3 = 66.67A, which requires an ampacity of at least 67A.

Question 3

Which of the following locations is explicitly prohibited for the installation of overcurrent devices, according to NEC 240.24?

Accepted Answer

In the bathrooms of dwelling units

Answer

NEC 240.24(E) states that overcurrent devices shall not be located in the bathrooms of dwelling units, guest rooms, or guest suites.

Question 4

When is it permissible to use the next higher standard rating of an overcurrent protective device if the conductor's ampacity does not correspond to a standard size OCPD?

Accepted Answer

When the OCPD is rated 800A or less and other specific conditions are met

Answer

NEC 240.4(B) permits using the next higher standard overcurrent device rating, but only if the OCPD is rated 800A or less, the conductor is not part of a multi-outlet branch circuit serving cord-and-plug-connected portable loads, and the conductor's ampacity is not less than the continuous and noncontinuous loads.

Question 5

A 480V to 208/120V, three-phase transformer has a primary full-load current of 60A and a secondary full-load current of 167A. If both primary and secondary protection is provided, what is the maximum standard size overcurrent device permitted on the primary side?

Accepted Answer

150A

Answer

According to NEC Table 450.3(B), for a transformer with a primary current of 9 amperes or more and with both primary and secondary protection, the primary overcurrent device can be rated at a maximum of 250% of the primary full-load current. 60A x 2.50 = 150A. Since 150A is a standard size OCPD listed in 240.6(A), it is the maximum permitted rating.

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Practice Test

FREE Journeyman Electrician’s Overcurrent Protection Questions and Answers