SubPanel Feed

[98softail]

I am putting a subpanel for my upstairs. The Main is a 200A and the inspector wants a 100A subpanel. One of my electrician friends told me to use #4 wire. My brother-in-law (also an electrician) said I should use #2 wire.

Which is right? Also, what size conduit should I use?

I want to make sure it is done right.

[Sparks]

They're both right. 4 awg copper or 2 awg aluminum. As for pipe size, 1.25" or 1.5" will work, I would go with whichever is cheaper in your area. 1" would work with copper but the pull might be tough if it's long. Use lots of wire lube as to not damage the conductors. Although being in Pipe Country (Chicago) I would go with THHN wire #4 and at at least a 1" diameter conduit. Remember you will need a 4 wire feeder and isolating the grounds and neutrals is a must in the sub panel but I'll bet they already told you that.

[98softail]

Thanks Sparks!

I did confirm this also with another friend and the CodeCheck book.

Do I need to have a grounding conductor if I am using conduit?

[Sparks]

Technically NO, you do not need an actual wire for the grounding conductor, the pipe (emt) technically will accomplish this providing you are diligent in tightening every lock-nut wrench tight and tightening every set screw until it bottoms. Keep in mind though, that many engineers are specifying a redundant grounding conductor when they draw up plans and many well informed contractors are also not relying on conduit grounding paths any longer. The actual grounding wire is cheap insurance when you consider this is a life safety issue. I would recommend for a sub-panel that you run a 4 wire feeder, that's my opinion but it is not required by code. Now if you were just wiring a ceiling fan and running emt, no problem, but for a sub-panel, that's a little more critical in my book. Sounds like you are doing your homework, good luck on the project.