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Old 02-27-2017, 12:21 PM   #1
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Default wiring for a welding receptacle

I've got a mid-1980s model Miller welding machine that I use for home use. It's a pretty beefy machine. Rated 90A at 230VAC input. Code lets me rate the supply conductors at 63% of nominal input current due to the duty cycle of the machine. Minimum supply wires (63% x 90A = 56.7A --> 65A rated wires), and breaker rated not more than 200% of the nameplate current of the machine. Sooo, I've got #6 THWN wires between a 100A breaker and a dedicated receptacle for the welding machine.

Are any of you aware of a code rule that would allow me to install a dedicated receptacle for the welding machine that is rated less than the breaker serving the circuit?

Its a short duty application, and I'm not the least bit worried about burning anything up, but I'm a code nerd, and I like to do NEC compliant work, even when it's my own stuff in the garage.

I'm currently using a 50 amp NEMA range receptacle for the welder. If I ever move out of the house, I'll probably rob the 100A breaker from the panel and tape off the wires feeding the 50A recep.

Been using the machine this way for several years. Funny enough, the #8 AWG stranded cord with 50A NEMA plug that came factory equipped on the machine has never even gotten remotely warm, even when I'm cranking the machine hard for several minutes at a time.

Last edited by McDaniel8402; 02-27-2017 at 01:28 PM. Reason: typo
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Old 02-27-2017, 05:57 PM   #2
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What does the manufacturer's instructions say about the OCPD & ckt ampacity, since it had a factory supplied 50A plug?
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Old 02-27-2017, 06:13 PM   #3
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Try it with a 50A breaker, unless you are welding 12" beads on 1/2" plate, bet it will be fine, then you don't need to worry about the rest.
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Old 02-27-2017, 06:27 PM   #4
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This isn't a welder outlet, it's an RV outlet and you can only install it based on what the outlet says on the front of it so that RV people can connect to it. Or so I've been told...
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Old 02-27-2017, 06:31 PM   #5
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This isn't a welder outlet, it's an RV outlet and you can only install it based on what the outlet says on the front of it so that RV people can connect to it. Or so I've been told...
I'd wager that a welder comes with a 3 wire cord end, and he put in a NEMA 10-50 receptacle, not a 14-50, you sour puss.
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Old 02-27-2017, 06:32 PM   #6
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Quote:
Originally Posted by HackWork View Post
This isn't a welder outlet, it's an RV outlet and you can only install it based on what the outlet says on the front of it so that RV people can connect to it. Or so I've been told...
Now you are figuring out this code thing. If it was hard wired he could do as he is now.
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Old 02-27-2017, 06:36 PM   #7
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I'd wager that a welder comes with a 3 wire cord end, and he put in a NEMA 10-50 receptacle, not a 14-50, you sour puss.
That doesn't matter, he can't put a larger breaker in.

What I said stands. If you are going to insult me with rude names, at least get it right.
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Old 02-27-2017, 06:45 PM   #8
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That doesn't matter, he can't put a larger breaker in.

What I said stands. If you are going to insult me with rude names, at least get it right.
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Old 02-27-2017, 06:59 PM   #9
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Stop crapping the thread. You should apologize to McDaniel8402.
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Old 02-27-2017, 10:35 PM   #10
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I don't think it matters what type of receptacle it is, Table 210.21(B)(3) allows only a 40 or 50 amp breaker to supply a 50 amp receptacle.

Could be wrong though, it's been a long hard day.........
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Old 02-27-2017, 11:11 PM   #11
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210.21(B) exception No. 2 allows a lower rated receptacle than the breaker but the OP's might be a little above a 50A receptacle. Probably have to use a L6-60R

Quote:
Exception No. 2: A receptacle installed exclusively for the
use of a cord-and-plug-connected arc welder shall be permitted
to have an ampere rating not less than the minimum
branch-circuit conductor ampacity determined by 630.11(A)
for arc welders.
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Old 02-27-2017, 11:19 PM   #12
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Hardwire or throw in a 100a pin and sleeve receptacle and cord cap. 100a Meltrics go pretty cheap on eBay (~150 for a matching set).

Pretty certain 50a is the max for a 50a receptacle according to 210.21(B)(3)
However 630.32 may allow you to upsize to a 60a breaker?
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Old 02-28-2017, 12:03 PM   #13
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Looking at the options, I'd hardwire it if it wasn't my own. Since it is my own, I'm not worried about it. I just kept wondering if I was overlooking something simple. I picked through article 630 on welders, and didn't find anything other than wire size and OCPD.

There just isn't a whole lot of call of receptacles that large in single phase.

Something else I thought of though. I could just as easily get a 3-wire 480V 100A plug and recep, and wire it 240.

And to those who suggested using a 50A breaker on it. You're probably right. It would likely hold. I'm afraid I've got a little too much "Tim the Toolman Taylor!!" in me.
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Old 03-01-2017, 09:34 AM   #14
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I run mine on #6 with a 50 amp breaker. I've grossly exceeded the duty cycle on my machine several times. No problems with the breaker tripping or the wire getting warm.
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Old 03-01-2017, 09:36 AM   #15
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Quote:
Originally Posted by McDaniel8402 View Post
Looking at the options, I'd hardwire it if it wasn't my own. Since it is my own, I'm not worried about it. I just kept wondering if I was overlooking something simple. I picked through article 630 on welders, and didn't find anything other than wire size and OCPD.

There just isn't a whole lot of call of receptacles that large in single phase.

Something else I thought of though. I could just as easily get a 3-wire 480V 100A plug and recep, and wire it 240.

And to those who suggested using a 50A breaker on it. You're probably right. It would likely hold. I'm afraid I've got a little too much "Tim the Toolman Taylor!!" in me.
Did you not see post #11?
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Old 03-01-2017, 10:44 AM   #16
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Quote:
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Did you not see post #11?
I did miss that one! Thanks for pointing it out.

As that post mentioned though, the minimum size recep would be a 60A.

I will file this away in mind for future reference.
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Old 03-01-2017, 05:20 PM   #17
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Welder receptacles per NEC

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit.
A single receptacle installed on an individual branch circuit
shall have an ampere rating not less than that of the branch
circuit.
Exception No.1: A receptacle installed in accordance
with 430. 8J (B).
Exception No.2: A receptacle installed exclusively for the
use of a cord-and-plug-connected arc welder shall be permitted
to have an ampere rating not less than the minimum
branch-circuit conductor ampacity determined by 630.11(A)
for arc welders.
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