Alan S
Aluminum
- Joined
- Oct 6, 2006
- Location
- Kintyre ND
I have added on to my shop I have put in a 250amp breaker box witch is 50ft from my sub panel. I need to know what size wire I need, and can my ground wire be smaller. Thanks Alan.
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It depends on several factors, primarily related to temperature.
My 2002 NEC rates 4/0 90°C THHN at 260 amps.
I would be inclined to use a larger gauge to keep the temperature down. The next larger one listed in the table is 250 kcmil.
This is pretty big stuff. Unless you have experience handling large wire and the tools to work with it properly, I would suggest letting a professional electrician do the work.
Three conductors of either size would require 2" conduit.
- Leigh
NEC Table 250-94 does allow smaller grounding electrode conductors in AC systems. For a 250 MCM conductor, the grounding electrode must be at least #2 copper, or #0 aluminum.can my ground wire be smaller
Three conductors of either size would require 2" conduit.
- Leigh
By NEC, but as always, local control may be different. I've just been through this here last week, and for example, my utility requires 3" conduit for three 4/0 conductors.
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