# MIG Welder Electrical Supply Circuit Specs



## exciterfan (Jul 9, 2012)

Hello,

I just bought a Lincoln WeldPak 180HD Wire Feed MIG Welder. The Welder is rated at 240V/20 Amps, 30 % duty cycle. The connection specifications state that it requires the 50 Amp receptacle (to match the plug supplied with the welder), and specs call for a 40 "Super Lag" breaker. That's all they say.

Normally for a 20 Amp circuit load, would require 30 amp breaker with #10 wire. A 30 amp circuit load would require a 40 amp breaker and #8 wire.

I'm assuming they are calling for a 40 amp breaker due to the inrush current required by the welder (much like the starting current on an electric motor). The Canadian Electrical Code "seems" to indicate that on circuits supplying loads like electric motors and welders, you are actually allowed to oversize the breaker or undersize the cable because the inrush current is only a momentary load. I've also read that the 30% duty cycle means you can undersize the conductors by a factor of 0.55 which means for a 20 amp load that would be 0.55 x 20 = 11 Amps, which would only require #14. But there is also a rule about overating the breaker by no more that 200%, which is where I think they came up with the 40 amp breaker spec, and that would disqualify #14 to be sure.

I'm thinking a 40 amp regular breaker with #10 wire should suffice in this application. I already have some #10 BX that I was hoping to use, but will buy #8 if I have to. I also think a regular 40 amp breaker should do as I've never seen a "Super Lag" breaker in the stores (and can only imagine the price tag for one).

Can anyone help me out by either confirming my assumptions or pointing me in the right direction.

Thanks


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## andrew79 (Mar 25, 2010)

Legally you can use the 10 bx. Personally I would feel better running 8's. You can probably get away with a 30a breaker as well. The inrush won't be that bad on the mig welder. Remember the code says "not more" you can go smaller.


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## exciterfan (Jul 9, 2012)

Hey thanks for the reply!!

Since I'm only going to use the welder only for hobby projects/casual use etc., I think #10 is sufficient, especially when you indicate that a 30 amp breaker would probably do the job (which means #10 AWG) anyway.

Thanks again!!


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## silversport (Feb 4, 2012)

Not that this is very helpful because it is a different welder but I have a miller 211 with the following specs and run it on a 30A breaker with 10 AWG NM-B (and a 6-50R receptacle to match the supplied plug). Just a point of reference...

*Voltage (V): *230
*Input Amperes (A) At Rated Output: *24.3
*Max Recommended Standard Fuse Rating In Amperes*
*---Time-Delay Fuses: *25
*---Normal Operating Fuses: *35
*Min Input Conductor Size In AWG: *14


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## Stubbie (Jan 7, 2007)

exciterfan said:


> Hey thanks for the reply!!
> 
> Since I'm only going to use the welder only for hobby projects/casual use etc., I think #10 is sufficient, especially when you indicate that a 30 amp breaker would probably do the job (which means #10 AWG) anyway.
> 
> Thanks again!!


 
Don't make this complicated ... the welder comes with a power cord with a NEMA 6-50 P plug so you will need a nema 6-50 R in the wall. The golden rule here is let the plug be your guide. So wire the branch circuit accordingly and per the manufacturer instructions. #10 wire and 30 amp breaker is not what the manufacturer is calling for you to use.


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## andrew79 (Mar 25, 2010)

Lincoln puts a 50a plug on almost all their welders so they don't have to carry different stock. My uncle's a manager at the Canadian division and I spent some time there before I got into the trade. The 30a breaker and 10 wire is all you need.


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## exciterfan (Jul 9, 2012)

Just to be clear, I was NOT going to use a 30 ampre breaker. I was planning to install a 40 amp breaker and use #10 AWG cable. The manufacuturer (Lincoln) does NOT state the cable size required for the supply only the full load ampres (20 Amps) and a breaker size of 40 Ampres.

I believe my proposed solution is within the Canadian Electrical Code..


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## silversport (Feb 4, 2012)

stubie said:


> Don't make this complicated ... the welder comes with a power cord with a NEMA 6-50 P plug so you will need a nema 6-50 R in the wall. The golden rule here is let the plug be your guide. So wire the branch circuit accordingly and per the manufacturer instructions. #10 wire and 30 amp breaker is not what the manufacturer is calling for you to use.


This isn't universally true for 240V welders. Mine also came with a NEMA 6-50P plug and the specs (taken directly from the manufacturer's literature) are listed in my post above....


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## andrew79 (Mar 25, 2010)

That's a grey area. Technically your not allowed to size your breaker any bigger than the allowable ampacity of the wire. I'll check out the code as soon as I get a second.


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## exciterfan (Jul 9, 2012)

I'd really appreciate you checking the code book for me, because the summary I have states that for large loads like a motor or a welder, the CEC:

"permits the ampre rating of the main supply breaker to be greater than the actual cable rating." This came from the sub panel section I believe.


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## zappa (Nov 25, 2011)

exciterfan said:


> I'd really appreciate you checking the code book for me, because the summary I have states that for large loads like a motor or a welder, the CEC:
> 
> "permits the ampre rating of the main supply breaker to be greater than the actual cable rating." This came from the sub panel section I believe.


I wouldn't think a motor and a welder are the same type of load.


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## mpoulton (Jul 23, 2009)

andrew79 said:


> That's a grey area. Technically your not allowed to size your breaker any bigger than the allowable ampacity of the wire. I'll check out the code as soon as I get a second.


It's not a grey area or a technicality. The code is clear. For motors and welders, different rules apply and larger breakers are allowed on smaller wire. The reason is that the breaker provides only short-circuit protection, not overload protection. The load itself contains thermal protection devices that prevent overload.

You can size the wire to the load (20A here, so #12 would be allowed) and the breaker to the manufacturer's instructions (40A) or according to the tables in the code. So it would be legal to use a 6-50R receptacle with #12 wire and a 40A breaker. But that's weird, and the receptacle must ONLY be used for this welder then. Personally, I would run a 50A breaker and #8 wire so the receptacle would be usable with other equipment in the future.

Also, it's worth noting that the 20A rating already takes the 30% duty cycle into account. The actual current draw while welding is much higher (probably over 40A, since they specify a time delay breaker). It's not a momentary inrush, it's just that you can't maintain an arc continuously for all that long and they expect you to be welding no more than 30% of the time.


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## curiousB (Jan 16, 2012)

I have a similar welder and I run it off of a 240VAC @15A branch circuit with NEMA 6-15 style plug on welder and receptacle. I have never tripped a breaker. If I did it again I would put in 12 AWG to a NEMA 6-20 plug with a 20A dual pole breaker but I was using existing wiring so compromised.

I suspect your plan of 10AWG has plenty of safety margin. To be safe though I wouldn't put a breaker over sized on the circuit even if an obscure section of NEC allows it. It just doesn't seem like a good idea. Put in your 10AWG with a 20 or 30A breaker and then re-evaluate later. I bet it never trips even at 20A, but you are perfectly fine with 30A. Better to err on over sized wire gauge than going the other route.


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## exciterfan (Jul 9, 2012)

Thank you to everyone for your responses.

mpoulton: Your response has shed much light on my quest. If you apply the 0.55 30% duty cycle factor adjustment on the rated 20 Amp current draw (i.e. 20 / 0.55 ), you get 36 Amps full load maximum. That's why they call for a 40 Amp breaker. :yes:

Nothwithstanding the logic of making the receptacle "universal" (i.e. not just dedicated to this particular welder), I will go with the 40 amp breaker and #10 AWG wire. This welder is going to be the largest electrical load in my shop for sure so I won't be plugging in anything heavier (I'll even label the receptacle accordingly). I also have the #10 BX cable already.

If I ever move away, I'll swap out the 40 amp breaker with a 30 amp breaker making the circuit safe for non-welder loads.

Thanks again everyone.


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## curiousB (Jan 16, 2012)

exciterfan said:


> I will go with the 40 amp breaker and #10 AWG wire. This welder is going to be the largest electrical load in my shop for sure so I won't be plugging in anything heavier (I'll even label the receptacle accordingly). I also have the #10 BX cable already.



Since a DP breaker is only $12 or so I would encourage you to put in the 30A and see how it goes. If you sustain nuisance trips you can put in a 40A later. As I said I am getting by with 240VAC @ 15A without a single trip. I just think you'd be safer not putting in such a larger breaker.


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## andrew79 (Mar 25, 2010)

So according to the CEC the smallest you can go wire size is 19.6A but when you derate for 80% you find you need tens at minimum. It's a 200% increase in breaker size so the biggest breaker you can use is either 200% of the max amps of the unit OR 200% of the allowable ampacity of the wire your using. Whichever is smaller.

:laughing: the long an short of it is you were A ok with what you said in your original post. As for the receptacle size the cec say's nothing about going bigger, only that you can't have a receptacle on a branch circuit rated at less than the overcurrent protection.

I always like to cover my butt though so i would probably use the 30A breaker to protect the wire but your good to go either way.


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## Yoyizit (Jul 11, 2008)

I get 67A while the arc is struck and with a 40A breaker with this trip curve
http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf
an arc lasting longer than 70 to 400 seconds would trip the thing.


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## curiousB (Jan 16, 2012)

Well all I can say is my MIG welder is 240VAC @ 21A (120A 20% duty cycle welding current at max setting) and I have never tripped a 15A branch breaker.


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## exciterfan (Jul 9, 2012)

andrew79 said:


> So according to the CEC the smallest you can go wire size is 19.6A but when you derate for 80% you find you need tens at minimum. It's a 200% increase in breaker size so the biggest breaker you can use is either 200% of the max amps of the unit OR 200% of the allowable ampacity of the wire your using. Whichever is smaller.
> 
> :laughing: the long an short of it is you were A ok with what you said in your original post. As for the receptacle size the cec say's nothing about going bigger, only that you can't have a receptacle on a branch circuit rated at less than the overcurrent protection.
> 
> I always like to cover my butt though so i would probably use the 30A breaker to protect the wire but your good to go either way.


andrew79: I was just woindering where you came up with the 19.6 Amps? Where in the code?


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## andrew79 (Mar 25, 2010)

36a full load times .55, you have to use the full load amps not the calculated duty cycle amps to get your new wire size. Standard rule is you can only load to 80% for any wire or breaker not rated for 100% use. So you need wire capable of handling 19.6/4*5 which gives you 24.5a. Might want to double check that as I don't have a calculator handy.


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## exciterfan (Jul 9, 2012)

The welders specifications actually show the full load amps at 20 Amps, so applying the 80% rule to that number would make it 25 Amps. #10 is okay.

Thanks again for your help.


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## Yoyizit (Jul 11, 2008)

curiousB said:


> Well all I can say is my MIG welder is 240VAC @ 21A (120A 20% duty cycle welding current at max setting) and I have never tripped a 15A branch breaker.


21A x 100%/20% = 105A which is a 7x overload for a 15A breaker. 
Using the same trip curve, you might get away with it if your arc duration is less than 2 to 8 seconds. 
Or maybe your breaker contacts are welded closed.

Sounds like I'm going to be e-mailing welder makers for an interpretation.


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## exciterfan (Jul 9, 2012)

Yoyizit said:


> 21A x 100%/20% = 105A which is a 7x overload for a 15A breaker.
> Using the same trip curve, you might get away with it if your arc duration is less than 2 to 8 seconds.
> Or maybe your breaker contacts are welded closed.
> 
> Sounds like I'm going to be e-mailing welder makers for an interpretation.


I think you should be dividing by 0.80 (80%) and not 0.20 (20%). IF the welder was drawing 105 amps at 240VAC on the input side, the current on the output or secondary side (i.e. the Arc) at 34 volts would be huge (>750 AMPS)!!:no: 

The welding current is more in the order of 130 amps based on the specs of my welder. :yes:


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## curiousB (Jan 16, 2012)

Yoyizit said:


> 21A x 100%/20% = 105A which is a 7x overload for a 15A breaker.
> Using the same trip curve, you might get away with it if your arc duration is less than 2 to 8 seconds.
> Or maybe your breaker contacts are welded closed.
> 
> Sounds like I'm going to be e-mailing welder makers for an interpretation.


It's 21A on 240VAC side, 120A at welder tip. Breaker is fine, I've tripped it with a space heater or two (before N gas furnace added) and I've switched off power a few times.

130A welder is only 9% higher than 120 so if a 15A @240V is working fine for me I can't imagine why a 40A is needed or advised. But that's just me.


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## andrew79 (Mar 25, 2010)

Yes but were talking about the op's welder which has rated current not full load amps. His fla is 36a. None of my replies were ever directed towards you. The 19.6a is from the conductor size you can use which is found by taking the Fla at a factor of .55 for a 30% duty cycle.


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## Yoyizit (Jul 11, 2008)

The company responds without answering my question and without directly saying that they refuse to answer my question.
The generator companies that I asked are going the same way.

". . .will draw 20 Amps of current at rated welding output. The rated output of this machine is 130 Amps @ 20 Volts when used at the 30% duty cycle on a 230 Volt AC supply."

130Ax20V = 2600W = 11A @ 230V
???

Maybe if I learned Japanese I could finally talk to a factory applications engineer. 
These marketing people should have been politicians; the money's better and they can probably have all the women they want.


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## curiousB (Jan 16, 2012)

Yoyizit said:


> The company responds without answering my question and without directly saying that they refuse to answer my question.
> The generator companies that I asked are going the same way.
> 
> ". . .will draw 20 Amps of current at rated welding output. The rated output of this machine is 130 Amps @ 20 Volts when used at the 30% duty cycle on a 230 Volt AC supply."
> ...


Yes there is some funny rating going on here and it seems like safety factor after safety factor over applied. Sure it enhances safety but with seemingly no regard to cost.

The welder is basically a current transformer stepping down the 240VAC to roughly 24 VAC (about 10:1) and then passing the AC through a bridge rectifier and a capacitor. That will bring DC to the Open Circuit voltage of 34 as specified in the specs. (1.4x pickup, AC RMS to DC).

Working backwards then if the welding current is 130A and it is going through a 10:1 transformer then the current on the 240 VAC must be around 13A. Why they specify a 40A slow response breaker is beyond me. As for the initial current surge upon striking the arc, that seems to be the job of the electrolytic capacitor after the bridge rectifier. 

It smells to me like cascaded conservative assumptions. As a result users are spending more on wire that really needed. It also explains why my 120A welder never trips a 15A @ 240VAC circuit.


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