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ronelu · Feb 4, 2009, 01:25 PM

From a main 200 amp house electrical panel what kind of wire do I need to put in two remote sub-panels for a 100 amp service and a 50 amp service.

Also, without tearing out walls to string new wire, can I use some existing wire runs that are not being used that have the following markings: First is "AL CAN S STABILOY (R) AA-8000 SERIES TYPE SE CABLE STYLE U TYPE KHHW CORS 600V 3CDRS 4AL UL 1989" & Second is "VP 2 CORS AWG4 1 COR AWG 4 TYPE SE CABLE 600V UL TYPE THHN" and how many circuits could I run off each sub-panel?

(I have square-d QO panels now; do you have recommended panel models?)

My last questions for now is if these cables only have 3 conductors, do I have to add a ground at the sub-panel box; if so, how big & what type should the ground wire be & how do I gorund it since this would be in a basement and would have to go external somehow to get a rod in the ground... perhaps ground to a water pipe?

Thanks for any help you can give.

rwinterton · Feb 4, 2009, 05:56 PM

I'm not an electrician, so I'd definitely check with my local inspector first, but I'd probably run 6 gauge copper to the 50-amp service and 1 gauge copper to the 100 amp service.

I believe you do have to add a ground wire. I'm not sure if you need two sources of ground for sub-panels or not. I doubt it. I'd probably connect a ground wire to the main service panel. I'm not sure about sizing it. Maybe the same size as the main copper wire.

stanfortyman · Feb 4, 2009, 07:39 PM

OK, you cannot use that cable. It is only SEU and that does not have enough conductors. You cannot simply add a ground wire to it.

You need three feeder conductors and one equipment ground. A panel in a remote building also does need a ground rod. This is NOT another source of "ground". The equipment ground run with the feeder, and the ground rod, serve two completely different purposes.

For 50A you should run three #6cu for the feeders and you can drop to a #10cu for the ground.
For 100A you should run three #3cu with a #8cu ground.

Since you have a QO panel now I'd stick with that for your sub-panel. You also DO need a means of disconnect at this remote building. A main breaker is the easiest way to achieve this. Don't forget you need to leave out the bonding jumper (green screw) in the sub-panel and install an add-on ground bar and keep the grounds and neutrals separate.