Many people use #4 AWG copper wire to supply a 100A sub-panel. Do not do this. There is a lot o...
May 01, 2018
Verified Purchase & Recommended Product
Many people use #4 AWG copper wire to supply a 100A sub-panel. Do not do this. There is a lot of confusion on proper interpretation of NEC application here. But in almost all cases, to be fully compliant, #3 AWG copper wire must be used. For a sub-panel application, in most cased, #4 wire is only listed for 85 amps. In this case, it is acceptable to protect with the next size up breaker (90A). So if you have a sub-panel supplied by this #4 wire, you should have a 90A breaker in your main panel protecting that sub-panel. I am shocked that HD does not carry #3 in the store given how common 100A sub-panels are.