For 12 AWG copper conductors, the permissible overcurrent protective device rating is 20A.

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Multiple Choice

For 12 AWG copper conductors, the permissible overcurrent protective device rating is 20A.

Explanation:
The key idea is that the overcurrent protection device cannot exceed the ampacity of the conductors it protects. For 12 AWG copper, the typical insulation used in common branch circuits (such as NM-B) is rated for 60°C, and the NEC tables list the ampacity of 12 AWG copper as 20 A at that temperature rating. That means an overcurrent device protecting this conductor cannot be larger than 20 A. If the insulation and terminations were rated higher (75°C or 90°C) and everything in the circuit is compatible with those ratings, higher OCPD values (25 A or 30 A) could be used, but with standard 12 AWG copper in typical residential wiring, 20 A is the maximum. A 15 A device is technically allowable but smaller than the maximum.

The key idea is that the overcurrent protection device cannot exceed the ampacity of the conductors it protects. For 12 AWG copper, the typical insulation used in common branch circuits (such as NM-B) is rated for 60°C, and the NEC tables list the ampacity of 12 AWG copper as 20 A at that temperature rating. That means an overcurrent device protecting this conductor cannot be larger than 20 A.

If the insulation and terminations were rated higher (75°C or 90°C) and everything in the circuit is compatible with those ratings, higher OCPD values (25 A or 30 A) could be used, but with standard 12 AWG copper in typical residential wiring, 20 A is the maximum. A 15 A device is technically allowable but smaller than the maximum.

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