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I am installing an outlet in my garage for a 240v mig welder. The welder specs call for 30A breaker.

The outlet for the welder is only 2 feet from the garage sub panel. The wiring reference charts I've seen say I can use 12 gauge copper wire for this short of a distance. Does this make sense? I would have expected it to say that 10 gauge copper wire was the smallest acceptable wire to use.

The reason I'm even asking is that I am also wiring the garage for an air compressor and an air conditioner. Both will be on their own 240V 20A breakers. They will be located about 30 wire feet (one way) from the sub panel. This will require enough wire that it makes financial sense to buy the smallest gauge that will work safely and meet code.

According to an online calculator I could even use 14 gauge copper wire.

Realistically, what wire gauge copper wire should I install in my garage for these tools?

isherwood
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Scott Bruns
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3 Answers3

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The calculator you referenced is only appropriate for voltage drop and makes the disclaimer that the results of the calculation do not account for current specs or NEC. Any circuit fused for 30 amps must use a minimum of 10 ga copper or 8 ga alu. Longer runs may require an upgrade of wire size. In your case, use at least 10 copper for your welder regardless how far it is from the breaker panel. I'm sure one of my buddies here will have a NEC ref for ya.

shirlock homes
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I am not a lawyer, electrician, or welder. I have a 1970s Miller 250 amp AC/DC welder with 12 ga power cord and a NEMA 6-50 plug on it. That made me curious and I found that NEC does or at least did allow you to up-rate wire for reduced duty cycle welders. The receptacles do have to be marked For Welder Use Only. So, I guess you could use 10 ga wire with a 60 amp breaker if it was only used for a welder with 50% or less duty cycle. That said, I use 6 ga wire with a 50 amp breaker and either a NEMA 6-50 or 14-50 receptacle for all of my single phase small to medium size welders and plasma cutters.

Mark
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We'll assume you're in a jurisdiction where your laws adopt the NFPA's national electric code (NEC) standard. As of NEC 2017:

Although 10 AWG copper wire can carry 35 A at 75° C per NEC 310.15(B)(16), NEC 240.4(D) specifies the maximum allowable overcurrent protection (i.e. circuit breaker) as 30 A.

For these small wire sizes (as specified in 240.4(D)), run length is not considered. Voltage is irrelevant to current capacity.

ndemarco
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