wire load callculations

[danbel57]

After adjusting for correction factors in sizing a wire to the load, you frequently end up with a wire that has a greater amperage rating than the circuit breaker protecting that load. According to the code the amperage of the wire has to be protected by the circuit breaker. However, if you have to increase the circuit breaker to protect the wire, you are no longer properly protecting the load it serves. Any thoughts?

 

[roger]

As long as the conductors ampacity is equal to or above it's protection all is fine. You could protect 1000 KCMIL with a 10 amp breaker if you wanted to.

Roger

 

[Smart $]

After adjusting for correction factors in sizing a wire to the load, you frequently end up with a wire that has a greater amperage rating than the circuit breaker protecting that load. According to the code the amperage of the wire has to be protected by the circuit breaker. However, if you have to increase the circuit breaker to protect the wire, you are no longer properly protecting the load it serves. Any thoughts?

Except for 240.4(B) allowing a higher rated ocp, Roger covered the issue. The ocp rating never has to be upsized to protect the conductor. It's the other way around. The conductor may have to be upsized so that it is protected by the ocp.