I'm planning to replace my existing sub panel outside of the house and the wire. The main is in the laundry room and it will run into the attic and out to the opposite side of the house which already has a conduit installed. Reason why I'm replacing the wire because who ever the previous owner has installed the sub panel only use one wire to connect both terminal to power the sub panel.

My plan is to install a 60 amp panel, using 4 gauge (3 conductors with ground), but I'm not sure if I should use SER, NM-B, or start with NM-B then connect to THWN, or any other option? The wire will be 100ft run from the main to the sub panel.

  • 1
    If you have a complete conduit run, cable is the wrong choice, and you can simply add one or more wires, not replace everything, unless it's also the wrong size, etc.
    – Ecnerwal
    Apr 21, 2023 at 0:36
  • The conduit had already been installed outside of the house where the wires will be expose to the weather, not in the attic.
    – user165940
    Apr 21, 2023 at 9:01
  • NEC 312.5(C) imposes significant restrictions running cable assemblies in conduit from "cabinets". See diy.stackexchange.com/questions/104848/… for NEC quoted. Apr 21, 2023 at 17:19

1 Answer 1


From what is mentioned on this site 2-2-2-4(?) aluminum wire is the best cost wise.

I think it is good for 90 amps so you could upgrade the panel in the future or now.

Bigger panels usually do not cost more and become much cheaper to install first, than to replace with bigger in the future.

Can downsize a big amp panel with a smaller size breaker feeding it, can't increase a small amp panel.

  • My main is 150 amp, will I need to upgrade my main to 200 if I do decide to go for 90 amp and will the 2-2-2-4 al wire be good for 100 ft run or is a bigger wire needed? I also think that I don't really need 100 amp that's why I'm going with 60amp.
    – user165940
    Apr 21, 2023 at 10:08
  • @user165940 That is the good thing about panels. They are listed for the maximum amps, but you could feed a 200 amp panel with a 30 amp breaker if you wanted(30 amp breaker can not fit 2 gauge) but you get the idea. You probably just 100 amp panel unless you have plans for future expansion, the main thing is to get as many breaker spaces as you can.
    – crip659
    Apr 21, 2023 at 11:02

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