4 posts in this topic

Hello,

I am sizing a feeder circuit for a panel according to UL 508A and came into a question:

My input current is of 76.5 A (considering all the loads), thus, it is fine for me to use a cable of 4 AWG (max. 85A @ 75 c).
For the circuit breaker I did 76.5 A x 1.25 = 96 A and then I selected a breaker of 100A.

My question is: 
Is it ok for me to keep this configuration according to UL 508A? 100A breaker + 4 AWG load side cable
Or do I need to level up the cables?

Thank you very much in advance!

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The purpose of the breaker is to protect the wire and it's insulation from melting or starting a fire.  If the breaker is oversized for the wire, then you are essentially protecting nothing.

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Spec the wire at 125% of maximum possible load.
Spec the breaker at 90% of the wires load rating.
In most locales this should exceed the code requirements.

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