Ground Wire Size

8 years ago

I'm thinking about putting a 60 amp subpanel in a garage/workshop that's about 100 feet from the house. From the main panel I would probably need about 125 feet of wire and because of voltage drop I would need to use #4 copper. What I am curious about is if I also need to up the size of the ground wire?? Or can it stay at #10?

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Comment (1)

Bruce in Northern Virginia
8 years ago
The ground wire for #6 copper is sized at #10, so if #6 is good enough for the current carrying wires, #10 is good enough for the ground. However, for runs greater than about 75 feet, #4 copper is recommended for a 60 amp circuit, so you need to go up to #4 copper.

You may want to look at 2-2-2-4 aluminum Mobile Home Feeder (MHF), since it is readily available in most stores. It would be rated for more than you need; however, it will also be quite a bit cheaper than running copper.

There is no significant downside to running aluminum to interconnect panels, since the terminals in modern panels are rated for aluminum. It is not the same risk that that made headlines when aluminum was used improperly for lower amperage circuits. Your main feed from the power company is probably aluminum.

Bruce
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