Sizing a welder disconnect?

Status
Not open for further replies.
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I have a customer that has a Miller Shopmaster 300 combination arc/mig/tig welder that is tripping the breaker frequently. It's rated at 91.2 amps/230v 1 phase/50% duty cycle.

http://www.millerwelds.com/om/o318q_mil.pdf

Currently it is being used on an existing 50 amp circuit with #8's feeding a 50 amp crows foot recep. It's definitely not cutting it. I've been through Art. 630 and I understand how to size the wire/breaker, but how do I size a cord end/recep if they decide to keep this same portable setup rather than hardwiring it?
 
Cow said:
I have a customer that has a Miller Shopmaster 300 combination arc/mig/tig welder that is tripping the breaker frequently. It's rated at 91.2 amps/230v 1 phase/50% duty cycle.

http://www.millerwelds.com/om/o318q_mil.pdf

Currently it is being used on an existing 50 amp circuit with #8's feeding a 50 amp crows foot recep. It's definitely not cutting it. I've been through Art. 630 and I understand how to size the wire/breaker, but how do I size a cord end/recep if they decide to keep this same portable setup rather than hardwiring it?
Click to expand...

I would say your cord end/recp. would need to be rated at or above your over-current protection.
 
I have had similar questions about the same subject.

You are talking about a fair sized welder. It is possible to be talking about a buzz box of some sort, with a low duty cycle that table 630.11 (A) would allow for some pretty small conductors.

It seems to me that you would have to hard wire it. Otherwise, why would the installation not just be some recepticle, no longer subject to the leniencies allowed by the welder duty cycle table of 630.11A.

Or should you size the cap and plug according to the reduced effective amperage allowed by table 630.11 (A) ?

Suppose you had a welder with a 50 A primary and a 20 duty cycle? Would you have a 100 A OCPD, # 10 Conductors, and a 100 A receptical?

The whole duty cycle concept seems kinda dumb to me, except for circuits having more than one welder.

If it's only one welder, I think just size the conductors to the OCPD and be done with it.
 
Last edited:
My brain is too slow for a 10 minute edit limit.

Also, by crow's foot are you talking about a #10-50, and if so, are those even kosher? Are those grounding?

( And if you put something else on, will you be able to plug it in in any other facility? )
 
This almost looks like a situation where a cord and plug is not a reasonable alternative. Since you have been through Art 630, you see the existing 50 amp is undersized. It appears to me, from Art 630, that we are looking at a 65 amp conductor with a maximum OCP of 150 amps. If you are cord and plug connecting the unit, would that not be your disconnecting means ?
If so, 630.13 would states it should be rated at the OCP level thus a 150 amp receptacle.
I would be interested in other opinions, but I am of the opinion that, since anything can be plugged into a receptacle, the receptacle must be rated at the OCP level and have appropriate sized conductors.
Looks like a "hard wire" solution to me.
 
realolman said:
IMO, that is the key thought, and Art 630 does not apply.
Click to expand...

That makes a lot of sense. The requirement to have a disconnecting means that is a switch or circuit breaker (not a receptacle) gives more support to this line of thinking (that you can't use a receptacle and wire/breaker sizes of 630 to feed the receptacle).
 
Status
Not open for further replies.
Top