Master Electrician Exam (NEC)Overcurrent ProtectionEasy
A branch circuit supplies power to a 120V, single-phase, 15-ampere non-continuous load in a dwelling unit. The circuit conductors are 14 AWG copper with 90°C insulation. What is the maximum standard overcurrent device rating permitted for this circuit, assuming no other limiting factors?
- A15 amperes
- B25 amperes
- C20 amperes
- D10 amperes
Show answer & explanationAnswer & explanation
Correct answer: A. 15 amperes
According to NEC 240.4(D), for 14 AWG copper conductors, the maximum overcurrent protection is 15 amperes, regardless of the insulation temperature rating. This rule is for conductor protection, not ampacity.
Why the other options are wrong
- B. 25 amperes is too high for 14 AWG copper conductors.
- C. 20 amperes is not permitted for 14 AWG copper conductors, even with higher temperature insulation, under general branch circuit rules.
- D. While 10 A is a valid OCPD size, 15 A is also standard and the maximum permitted for 14 AWG.
14 AWG OCPD Limit
Regardless of insulation temperature rating, 14 AWG copper conductors used in general branch circuits are typically limited to a maximum 15-ampere overcurrent protective device.
- NEC 240.4(D) specifies limits.
- Applies to 14 AWG copper.
- Maximum OCPD is 15 A.
Memory trick: Protecting 'wires' from 'too much current' is 'critical'.