NEC Interpretation (Multiple Welders on Single Branch)

[brianpgriset]

NEC newby here.

Goal is to install branch circuit for two transformer welders for upcoming garage redo. I will be the only person using either at the same time.

Based on the provisions of 630-11(b), am I correct in saying i can size the conductors based on the larger of the two using part (a) of the same section (ie the larger welder requires 6awg NM-B based on rated primary current multiplied by the duty cycle correction factor, therefore I need not size conductors any larger since I will never use either one at the same time )?

Thanks!

 

[nehog]

Size the conductors based on the breaker. Size the breaker based on the largest load.

 

[brianpgriset]

Size the conductors based on the breaker. Size the breaker based on the largest load.

I don't think that's right. 630-12(b) specifically allows over-current protection up to 200% of the conductor rating.

 

[rockwithjason]

what edition of the code are you using?


reading out of the 2011 edition it seems that conductors must be sized based on the sum of the current ratings of the two largest welders since you only have two welders it appears that you must size the circuit based on the full load of both units.

 

[sberry]

You cant derate conductors for the machine in relation o the breaker and them put 2 machines on. This leave the potential to overload the wires, I wouldn't have a real problem with multiple outlets provided the breaker matched the wire but not over breaker for welders.

 

[dledinger]

When it is unlikely that the loads will be used simultaneously, you may size the cicuit to the largest load.

 

[brianpgriset]

When it is unlikely that the loads will be used simultaneously, you may size the cicuit to the largest load.

That's what I took the referenced section of code to say.

 

[sberry]

I am not a fan of this for a home brew deal for a couple of reasons. Welders that come factory wired with 50A should be on a 50A circuit with a 50A breaker and the others are designed to be on a dedicated circuit with wire and breaker installed to match the machine. Is this going to be a deal breaker to run another circuit?

 

[sberry]

The code isn't really a diy manual and while some of this is allowed this kind of circuit is really intended for an industrial supervised environment, multiple machines, etc. It may be a problem in a big fab shop to provide a dedicated circuit for every welder.

 

[Norcal]

Just run 2 circuits & be done with it, unless the circuit breakers are obscenely expensive (not likely unless obsolete) & long runs, it's going to be simpler.

 

[theoldwizard1]

I am not a fan of this for a home brew deal for a couple of reasons. Welders that come factory wired with 50A should be on a 50A circuit with a 50A breaker and the others are designed to be on a dedicated circuit with wire and breaker installed to match the machine. Is this going to be a deal breaker to run another circuit?

Why bother. Just make sure there is only one outlet and each welder has the correct plug.

Why do people want to make things difficult !

 

[sawbuck]

Why bother. Just make sure there is only one outlet and each welder has the correct plug.

Why do people want to make things difficult !

that's what I did ....KISS...keep it simple stupid..

 

[dledinger]

Why do people want to make things difficult !

I agree. Not worth losing sleep over.

 

[sberry]

Some of these monsters are hard wired, cheaper to run a circuit than a plug. Probably not such an issue with a machine that needs a 6 wire,,, but we are not sure what model machines these are,, this should really be included at the start of one of these threads.

 

[brianpgriset]

Beta-Mig 250 and a Syncrowave 200.

Both already have plugs. My main concern is code compliance.

 

[sberry]

I don't think the synch comes with a plug and the 250 is a 50A machine if I recall correctly. Diff3erent breaker requirements. Use 2 circuits. BTW, a 200 synch will run on a 50 just fine though,,, I believe it lists a 60 but that would be screaming on the top end , really unlikely or for so short a duration it doesn't matter. If you are using a 6 cable and a 50 just plug either in to the circuit.

 

[pattenp]

I think in Texas you can do things not allowed elsewhere. Here in Virginia, the residential building code doesn't allow multiple outlets that are over 20 amps on a single circuit. Here you have to have a dedicated circuit for each welder outlet.

 

[CoopVA]

pattenp is correct.

It's not a wise idea to put multiple welders on the same circuit, no matter what the NEC says. Your Local Jurisdiction Having Authority more than likely will prohibit it also.

It's just not good Industry Practice. I've been in the Electrical Trade for over 20 years...

 

[sberry]

I can and I don't.

I will add that I might for a convenience outlet, I am inclined if I did this to make sure the wire breaker is a match and not de rated for a welder. There are some ways to do this for smaller machines, no real good way for larger ones in a small shop.

 

[bczygan]

Couldn't you install 2 receptacles on one circuit, sized for the larger welder, and a switch, so only one could be live at any time?

 

[larry_g]

Couldn't you install 2 receptacles on one circuit, sized for the larger welder, and a switch, so only one could be live at any time?

The cost of the switch and the associated hardware could easily equal the cost of the second circuit. Look up the cost of a 50a 3 way switch.

lg
no neat sig line

 

[CoopVA]

The cost of the switch and the associated hardware could easily equal the cost of the second circuit. Look up the cost of a 50a 3 way switch.

lg
no neat sig line

I agree. Keep it simple. The less breaks in the circuits the better.

 

[sberry]

As long as the wire was big enough to the breaker it would trip or if each wire to the machine was adequate for it and the combination tied on at the breaker or a big enough wire for the combined load it would be legal.

In theory we could run 2 Miller 211's at the same time from 50A circuit, each with a 12 wire or better hooked to a 50A breaker. If we hooked a buzz box to this circuit would need to insure only one machine at a time was used and we stayed within the duty cycle for that wire. We could alternate loads on the breaker at 100% but not on the wire.