Master Electrician Exam (NEC)Overcurrent ProtectionEasy
An electrician is installing a new 120V, single-phase circuit in a residential garage. The circuit supplies power to a single-gang receptacle for general-purpose use. What is the maximum overcurrent protective device (OCPD) rating permitted for a 14 AWG copper conductor feeding this receptacle, assuming the conductor is rated for 75°C?
- A10 amperes
- B25 amperes
- C20 amperes
- D15 amperes
Show answer & explanationAnswer & explanation
Correct answer: D. 15 amperes
For 14 AWG copper conductors, the ampacity in the 75°C column is 20 amperes. However, NEC 240.4(D) restricts the overcurrent protection for 14 AWG conductors to a maximum of 15 amperes, unless specific exceptions apply which are not present in this general-purpose scenario.
Why the other options are wrong
- A. This is below the maximum permitted rating and would be unnecessarily restrictive for a general-purpose circuit.
- B. This rating is too high for a 14 AWG conductor and would violate NEC 240.4(D).
- C. While 14 AWG conductors have an ampacity of 20 amperes at 75°C, the overcurrent protection is restricted to 15 amperes by NEC 240.4(D).
NEC 14 AWG OCPD Limit
The National Electrical Code (NEC) restricts the maximum overcurrent protective device (OCPD) rating for 14 AWG copper conductors to 15 amperes for most general-purpose applications, despite their higher ampacity ratings in temperature tables.
- NEC 240.4(D) specifies conductor protection limits.
- 14 AWG copper is generally limited to 15A OCPD.
- This is a common exception to the general ampacity rules.
Memory trick: Conductor Protection: 'Always Watch Limits'