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Electrical Code - USA Commercial or Residential 1999 / 2002 / 2005 versions - for UNITED STATES

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Old July 3rd, 2010, 05:56 PM
M_Swank M_Swank is offline
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Default Question about NEC code for welding circuits.

I'm hoping one or more of you out there will be able to help out with a couple of questions I have.

Here is some background information about my situation. I just purchased a Hobart Handler 187 wire feed welder. I need to set up a circuit on which the welder can operate. Based on what I have read in the owner's manual, and what I have read on the internet I have come up with the following information.

This Hobart welder has an input amperage of 20.5A and a duty cycle of 30%. Based upon NEC 630-11(a) I can take that 20.5A and multiply it by .55.

So, 20.5A x .55 = 11.275A. Am I correct in interpreting this information to mean that I can use #14 or heavier wire for my circuit? I think this is correct (plus the owner's manual from Hobart says #14 is the minimum wire size allowable).

A second point is that 630-12(a) leads me to believe that in order to determine the correct size of circuit breaker I must not exceed 200% of "the rated primary current of the welder". Does that mean that I take the 20.5A and simply multiply it by 2?

If so, that would give 20.5A x 2 = 41A. I am interpreting this to mean that I cannot use a breaker that is larger that 41A for the circuit (assuming that I match that breaker with a suitable wire size).

At this point I am of the belief that I could run a suitable circuit using #10 wire and a 30A breaker using a 6-50 receptacle.

However, why could I not just wire up a circuit using #6 wire, a 50A breaker, and a 6-50 receptacle? In the future I may purchase a stick welder with 50A input. Could I use such a circuit so that I could plug either machine into the same receptacle? I think this would be less of a hassle than running two separate circuits. I was prepared to install such a circuit but then ran into 630-12(a) on several discussion forums.

Any thoughts, inputs, corrections would be greatly appreciated.

Thanks folks.
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Old July 3rd, 2010, 10:55 PM
suemarkp suemarkp is offline
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I believe your math to be correct. I found it strange you determined you could use a #14 wire on a 40A circuit and then decided to go with 30A wire on a 30A circuit with a 50A receptacle...

There's nothing wrong with what you propose.

You may have a problem using the smaller welder on a 50A circuit -- that breaker may be too big for it. You could run a 60A feeder on #6 wire to a subpanel, then hang a 30A and 50A receptacle off of it using breakers of the same size. Then you could support both welders, but probably not both at the same time. I'd use 6-3 cable in the feeder so you have 120V available too should you ever need it.
Kent, WA
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Old July 5th, 2010, 02:31 PM
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Ohm1 Ohm1 is offline
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I believe your math to be correct. I found it strange you determined you could use a #14 wire on a 40A circuit and then decided to go with 30A wire on a 30A circuit with a 50A receptacle...
I didn't find it strange seeing that the op has pulled most his info from other sites. For the most part I agree with suemark, yet what's new.
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