So, what size wire for a 40 amp breaker do you need? The minimum wire size you can use with a 40-amp circuit breaker is 8-AWG. An eight-gauge wire is rated to handle a 40 amp breaker’s electric current. You can use a larger gauge 6-AWG wire for future-proofing, but a lower gauge wire will render the electrical system non-compliant with the NEC.

The recommended size wire for a 40 amp breaker is 8 AWG. This is the American Wire Gauge, and it is the standard that is used in the United States for determining wire size. 8 gauge wire is rated for 40 amps, and it can safely handle up to 50 amps. This 40 amp wire size can safely handle most needs.

The recommended wire size for a 40 amp breaker is 8 AWG. The 8 gauge wire is rated for 40 amps and has features to handle 50 amps. This 40 amp wire size can easily handle different values.