70 amp breaker with # 6 awg

feeder cable for subpanel in same building.

Yes or no?


#4 ,

Maybe. What is the wiring method? If it’s not NM cable then it might be OK. #6 THHN is good for 65 amps at 75° C. Next standard size OCPD is 70 amps.

Thanks Robert. I new there were exceptions, that’s why I asked. The wiring Is NM cable. I have an “electrician” arguing a little. Same “electrician” that failed to isolate the neutrals at same sub-panel.

You’re welcome. Since you have NM cable then the 60° C ampacity (55 amps) is the maximum permitted {334.80} even though the cable is made from 90° C conductors. If you had THHN in a raceway or MC cable then the 75° C ampacity may be used which is 65 amps. Since 65 amps is not a standard OCPD size in 240.6(A) then you can go up to the next standard size {240.4(B)} which is 70 amps.

With NM cable you’re stuck with the 60° C ampacity which is 55 amps, next standard size 60 amps.

So in answer to your question in the OP it depends on the wiring method. A #6 AWG feeder on a 70 amp OCPD may be compliant when it meets certain conditions. :cool:

Thanks Robert.