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Old 07-09-2012, 10:04 AM   #1
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 11:17 AM   #2
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 11:27 AM   #3
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 11:54 AM   #4
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 12:26 PM   #5
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MIG Welder Electrical Supply Circuit Specs


Quote:
Originally Posted by exciterfan View Post
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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Old 07-09-2012, 12:29 PM   #6
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 12:32 PM   #7
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 12:33 PM   #8
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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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Old 07-09-2012, 12:34 PM   #9
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 02:13 PM   #10
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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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Old 07-09-2012, 02:48 PM   #11
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MIG Welder Electrical Supply Circuit Specs


Quote:
Originally Posted by exciterfan View Post
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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Old 07-09-2012, 02:54 PM   #12
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MIG Welder Electrical Supply Circuit Specs


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Originally Posted by andrew79 View Post
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.

Last edited by mpoulton; 07-09-2012 at 02:58 PM.
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Old 07-09-2012, 02:56 PM   #13
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MIG Welder Electrical Supply Circuit Specs


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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Old 07-09-2012, 03:18 PM   #14
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MIG Welder Electrical Supply Circuit Specs


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.

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.

Last edited by exciterfan; 07-09-2012 at 04:19 PM.
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Old 07-09-2012, 07:36 PM   #15
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Originally Posted by exciterfan View Post
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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