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Old 09-17-2010, 05:31 PM   #1
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Default Welder branch circuit

I'm trying to figure out how to size branch circuits, over current protection and receptacle size for welders. Lets take this one for example:

http://www.millerwelds.com/pdf/spec_sheets/AC2-0.pdf

I'm assuming that the 47.5amps is the primary rated current with a duty cycle of 20%.

So:

.45 X 47.5 = 21.4amps minumum conductor ampacity.

If I'm understanding this correctly I could use #12 THHN protected by a 40 amp breaker to feed this welder and I could put a 30 amp receptacle on it. I need some help on this one.

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Old 09-17-2010, 06:11 PM   #2
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Quote:
Originally Posted by nitro71 View Post
I'm trying to figure out how to size branch circuits, over current protection and receptacle size for welders. Lets take this one for example:

http://www.millerwelds.com/pdf/spec_sheets/AC2-0.pdf

I'm assuming that the 47.5amps is the primary rated current with a duty cycle of 20%.

So:

.45 X 47.5 = 21.4amps minumum conductor ampacity.

If I'm understanding this correctly I could use #12 THHN protected by a 40 amp breaker to feed this welder and I could put a 30 amp receptacle on it. I need some help on this one.
Is it 60 degree or 75 degree rated?

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Last edited by BuzzKill; 09-17-2010 at 06:14 PM.
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Old 09-17-2010, 06:29 PM   #3
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The primary current is the rated KVA times 1000 divided by the primary voltage.
47.5 x (.45)= 21.375...for 60C or 75C equip. that'd be #12...200% x 21.375 = 42.75A breaker. Go with a 45A breaker.
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Old 09-17-2010, 08:20 PM   #4
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Thanks Buzz. Seems like most homeowner welders are plugged into circuits much larger than what they need.
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Old 09-17-2010, 09:10 PM   #5
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Originally Posted by nitro71 View Post
I'm trying to figure out how to size branch circuits, over current protection and receptacle size for welders. Lets take this one for example:

http://www.millerwelds.com/pdf/spec_sheets/AC2-0.pdf

I'm assuming that the 47.5amps is the primary rated current with a duty cycle of 20%.

So:

.45 X 47.5 = 21.4amps minumum conductor ampacity.

If I'm understanding this correctly I could use #12 THHN protected by a 40 amp breaker to feed this welder and I could put a 30 amp receptacle on it. I need some help on this one.
The circuit breaker should be a 2 pole 60 amp breaker. The receptacle required is almost certain to be a 60 amp pin and sleeve connector body. the exact type should be confirmed with the manufacturer. Probably a Hubbell type, might even be IEC. The circuit will require 2 #6 THHN and a #10 THHN ground. A smaller circuit breaker could trip out on overcurrent if the welder is operated at its full capacity.

for this equipment either a 208/120 volt industrial service or a 240/120 volt residential service is acceptable.
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Old 09-17-2010, 09:23 PM   #6
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show me your math
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Old 09-17-2010, 09:48 PM   #7
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Make sure you run a MWBC to the welding area to run lighting and a convenience receptacle.



















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Old 09-17-2010, 09:59 PM   #8
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Originally Posted by BuzzKill View Post
show me your math
There isn't any. Ampacity of circuits are sized based on the maximum current they will draw, in this case 47.5 amps. A 50 amp circuit breaker just might occasionally trip out if the welder is operated at its maximum setting especially if there is a momentary voltage drop during its operation. The circuit must also be sized for the receptacle supplied which is almost ceratin to be 60 amps. It is not likely that the inrush current to the transformer on turn-on would cross the time current curve of a standard 10,000 AIC 60 amp circuit breaker. But don't take my word for it, ask the manufacturer what he recommends if you don't believe me.

BTW...guess what......you're all off my bidder's list.
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Old 09-17-2010, 10:07 PM   #9
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Originally Posted by Shorty Circuit View Post
There isn't any. Ampacity of circuits are sized based on the maximum current they will draw, in this case 47.5 amps. A 50 amp circuit breaker just might occasionally trip out if the welder is operated at its maximum setting especially if there is a momentary voltage drop during its operation. The circuit must also be sized for the receptacle supplied which is almost ceratin to be 60 amps. It is not likely that the inrush current to the transformer on turn-on would cross the time current curve of a standard 10,000 AIC 60 amp circuit breaker. But don't take my word for it, ask the manufacturer what he recommends if you don't believe me.

BTW...guess what......you're all off my bidder's list.
hmmm, so you go on assumption alone or Article 630? Hell use 3/0 and a 200 amp breaker.
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Old 09-18-2010, 05:46 AM   #10
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Originally Posted by Shorty Circuit View Post
The circuit breaker should be a 2 pole 60 amp breaker.
It could be, but it is not required or needed to be.

Quote:
The receptacle required is almost certain to be a 60 amp pin and sleeve connector body.
It will have to be at least 60 amp rated if you use a 60 amp breaker. It is not required to be pin and sleeve.

Quote:
the exact type should be confirmed with the manufacturer. Probably a Hubbell type, might even be IEC.
Many welders ship without any cord cap, many others ship with straight blade. I would look at the cut sheet to know.

Quote:
The circuit will require 2 #6 THHN and a #10 THHN ground.
No


Quote:
A smaller circuit breaker could trip out on overcurrent if the welder is operated at its full capacity.
Yes it could, I could also hit the lottery. In other words not likely.


Quote:
Originally Posted by BuzzKill View Post
show me your math
Quote:
Originally Posted by Shorty Circuit View Post
There isn't any.
Well you can do it your way, and just provide way to much and if the client is fine with that all is good.

But if the client is putting this out to competitive bidding your way is no good at all.

Quote:
Ampacity of circuits are sized based on the maximum current they will draw, in this case 47.5 amps.
No, it is not really that straight forward for welders.

Quote:
A 50 amp circuit breaker just might occasionally trip out if the welder is operated at its maximum setting especially if there is a momentary voltage drop during its operation.
Yes it could, trip but that is low on the probability scale.

Quote:
The circuit must also be sized for the receptacle supplied which is almost ceratin to be 60 amps.
No, the circuit rating cannot exceed the receptacle rating but it can be less than the receptacle rating.

Quote:
It is not likely that the inrush current to the transformer on turn-on would cross the time current curve of a standard 10,000 AIC 60 amp circuit breaker. But don't take my word for it, ask the manufacturer what he recommends if you don't believe me.
Again, it could and the NEC addresses that.

Quote:
BTW...guess what......you're all off my bidder's list.
BTW...guess what......Shorty Circuit you're have been fired by the client due to your lack of knowledge about welder circuits.
  • Per the specs, this welder has a 20% duty cycle.
  • It has a current rating of 47.5 amps @ 230 volts.
  • I do not see an 'I 1eff' rating.

That said, per 630.11 the NEC minimum conductor size for this unit is 12 AWG.

47.5*.45=21.375 amps for conductor sizing. (Table 630.11(A))

For the over current protection 630.12 sets the requirements.

The breaker can be rated no more the 200% of the welder current or 200% of the conductors used which ever is less.

In this case the conductors I chose where 12 AWG with a rating of 25 amps

200% of 25 amps = 50 amps

So the NEC would allow 12 AWG supplied by a 50 amp breaker for this welder. Further more if that breaker opens needlessly the NEC allows rolling up one more size.

Now am I saying the above is the best way to go?

No

But if you happen to be taking tests based on the NEC you damn well better know about Article 630 and how to apply it.


Now, all that said, my experience with welders tells me that a unit like the one in the cut sheet with a 20% duty cycle will likely come with a 30 or 50 amp straight blade plug and I would simply provide a 30 or 50 amp receptacle to match wired with a 30 or 50 amp circuit.

With a 20% duty cycle the welder unit will either shut down or otherwise stop working before the circuit conductors can be damaged.

My own 225 amp welder works fine on a 30 amp circuit even when I was up in the 225 amp out put range.

It is all about the duty cycle, no one is going to use the machine in the cut sheet continuously at full output, at the least you are stopping to replace the rods.

Last edited by Bob Badger; 09-18-2010 at 06:41 AM.
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Old 09-18-2010, 05:47 AM   #11
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Hell use 3/0 and a 200 amp breaker.


The 3/0 would be allowed, the max breaker for that welder is a 90 or 100.
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Old 09-18-2010, 09:41 AM   #12
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Originally Posted by Bob Badger View Post
It could be, but it is not required or needed to be.



It will have to be at least 60 amp rated if you use a 60 amp breaker. It is not required to be pin and sleeve.



Many welders ship without any cord cap, many others ship with straight blade. I would look at the cut sheet to know.



No




Yes it could, I could also hit the lottery. In other words not likely.






Well you can do it your way, and just provide way to much and if the client is fine with that all is good.

But if the client is putting this out to competitive bidding your way is no good at all.



No, it is not really that straight forward for welders.



Yes it could, trip but that is low on the probability scale.



No, the circuit rating cannot exceed the receptacle rating but it can be less than the receptacle rating.



Again, it could and the NEC addresses that.



BTW...guess what......Shorty Circuit you're have been fired by the client due to your lack of knowledge about welder circuits.
  • Per the specs, this welder has a 20% duty cycle.
  • It has a current rating of 47.5 amps @ 230 volts.
  • I do not see an 'I 1eff' rating.
That said, per 630.11 the NEC minimum conductor size for this unit is 12 AWG.

47.5*.45=21.375 amps for conductor sizing. (Table 630.11(A))

For the over current protection 630.12 sets the requirements.

The breaker can be rated no more the 200% of the welder current or 200% of the conductors used which ever is less.

In this case the conductors I chose where 12 AWG with a rating of 25 amps

200% of 25 amps = 50 amps

So the NEC would allow 12 AWG supplied by a 50 amp breaker for this welder. Further more if that breaker opens needlessly the NEC allows rolling up one more size.

Now am I saying the above is the best way to go?

No

But if you happen to be taking tests based on the NEC you damn well better know about Article 630 and how to apply it.


Now, all that said, my experience with welders tells me that a unit like the one in the cut sheet with a 20% duty cycle will likely come with a 30 or 50 amp straight blade plug and I would simply provide a 30 or 50 amp receptacle to match wired with a 30 or 50 amp circuit.

With a 20% duty cycle the welder unit will either shut down or otherwise stop working before the circuit conductors can be damaged.

My own 225 amp welder works fine on a 30 amp circuit even when I was up in the 225 amp out put range.

It is all about the duty cycle, no one is going to use the machine in the cut sheet continuously at full output, at the least you are stopping to replace the rods.
"So the NEC would allow 12 AWG supplied by a 50 amp breaker for this welder. Further more if that breaker opens needlessly the NEC allows rolling up one more size."

Of all the nonsense you've ever posted, this strikes me as the most rediculous by far. NEC does not give a pass for experimentation to see what works and what doesn't.

All of the advice I gave are guesses based on my prior experience with welders. The only real way to find out is to contact the manufacturer or to get adequate specifications that indicate the manufacturers specified maximum overcurrent protection ampacity consistent with the UL rating of his product. This is invariably based on the time current curve of the equipment versus the time current curve characteristics of the overcurrent protection device whether it is a circuit breaker or a fuse. The exception of allowing a larger breaker than the ampacity of wire size it protects is for motors because the time current curve for a motor on startup is so large that a molded case breaker sized to allow it through without tripping, even an HACR rated breaker must be much larger than the motor running current. This exception is not made for welding transformers.

It is conceivalbe that 240 volts single phase could be obtained from a single phase transformer such as a large 480/240 volt tranformer with one leg of the secondary grounded. This would require a single pole breaker. But it is very unlikely. A two pole breaker is just about a certainty.

The cut sheet specified a connector but not what type. Usually I've found 100 amp pin and sleeve connectors typical. A 200 amp connector would have to be fed from a distribution panel, not an appliance panel as the largest branch circuit breaker for those panels are 125 amps. The only exception is a through feed to a 200 amp unit breaker or a sub feed breaker on the main bus if the panel is rated for it and configured to accept it.

BTW, do you have those feeders painted yet? I understand Home Depot is very good at matching paint colors to samples.
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Old 09-18-2010, 10:16 AM   #13
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Old 09-18-2010, 10:18 AM   #14
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Quote:
Originally Posted by Bob Badger
So the NEC would allow 12 AWG supplied by a 50 amp breaker for this welder.
Of all the nonsense you've ever posted, this strikes me as the most rediculous by far.
Well most would say posting without actually looking at the code sections mentioned is ridiculous.

Quote:
II. Arc Welders

630.11 Ampacity of Supply Conductors. The ampacity of
conductors for arc welders shall be in accordance with
630.11(A) and (B).

(A) Individual Welders. The ampacity of the supply conductors
shall be not less than the I1eff value on the rating
plate. Alternatively, if the I1eff is not given, the ampacity of
the supply conductors shall not be less than the current
value determined by multiplying the rated primary current
in amperes given on the welder rating plate by the factor
shown in Table 630.11(A) based on the duty cycle of the
welder.
(630.11(B) has to do with groups of welders and does not apply for this thread)

You will have to look in the NEC for the Table but a unit with a 20% duty cycle uses a 0.45 multiplier for the conductor sizing.

Quote:
Originally Posted by Shorty Circuit View Post
Quote:
Originally Posted by Bob Badger
Further more if that breaker opens needlessly the NEC allows rolling up one more size.
NEC does not give a pass for experimentation to see what works and what doesn't.
It does just that in a few articles.

As far as welders here it is.

Quote:
630.12 Overcurrent Protection. Overcurrent protection
for arc welders shall be as provided in 630.12(A) and (B).
Where the values as determined by this section do not correspond
to the standard ampere ratings provided in 240.6 or
where the rating or setting specified results in unnecessary
opening of the overcurrent device, the next higher standard
rating or setting shall be permitted.
As far as the rest of your post, just diversionary BS.

Come on, fess up, you are not an EE.

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Old 09-18-2010, 10:23 AM   #15
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Come on, fess up, you are not an EE.
Your endings are a classic..
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Old 09-18-2010, 10:40 AM   #16
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Well most would say posting without actually looking at the code sections mentioned is ridiculous.



(630.11(B) has to do with groups of welders and does not apply for this thread)

You will have to look in the NEC for the Table but a unit with a 20% duty cycle uses a 0.45 multiplier for the conductor sizing.



It does just that in a few articles.

As far as welders here it is.



As far as the rest of your post, just diversionary BS.

Come on, fess up, you are not an EE.
It is you who should confess that that you are not really an electrician. In all likelihood you are a painter.
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Old 09-18-2010, 10:40 AM   #17
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That was quite a thorough explanation on how to size conductors and ocp for welders...nice.
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Old 09-18-2010, 10:45 AM   #18
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It is you who should confess that that you are not really an electrician. In all likelihood you are a painter.
You are right, I am just a painter, not even a good one.

But I still know the NEC requirements for installing a welder.

I would have thought some one that says they have experience with welders would have known those rules.
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Old 09-18-2010, 11:21 AM   #19
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"You will have to look in the NEC for the Table but a unit with a 20% duty cycle uses a 0.45 multiplier for the conductor sizing. "

"The 3/0 would be allowed, the max breaker for that welder is a 90 or 100. "

In reviewing article 630 I've concluded you are correct. But just because you finally got one right, don't let it go to your head. I still don't believe you are an electrician. Maybe a handyman but not an electrician.
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Old 09-18-2010, 11:52 AM   #20
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Quote:
Originally Posted by Shorty Circuit View Post
"You will have to look in the NEC for the Table but a unit with a 20% duty cycle uses a 0.45 multiplier for the conductor sizing. "

"The 3/0 would be allowed, the max breaker for that welder is a 90 or 100. "

In reviewing article 630 I've concluded you are correct. But just because you finally got one right, don't let it go to your head. I still don't believe you are an electrician. Maybe a handyman but not an electrician.
Why the negative attitude and name calling.
The proper way to size the conductors and OCPD were explained with NEC compliance.
Instead of calling names, you should have thanked Bob for taking the time and effort to look all this up for you and the OP. He even pasted the articles for you.
Is it that hard to give credit where credit is due? We do not know everything. I know, I don't know everything that is.

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