240V welder

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grady180

grady180

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Hi - Does this seem to be correct for a 240 volt arc welder. This welder is going to be used in a residential garage. It has a primary current of 50A and a 20% duty cycle. I used a 30A breaker and 10-3 Romex to feed a 30A receptacle. The welder already had a 30A plug - looks like it had been replaced at some point and I'm not sure what it originally had. The owner complained of the breaker tripping after 10 minutes or so of use. If my calculaions are correct I should be able to replace the breaker with a 50A.

My calculations - 30A x .45(20% duty cycle multiplier NEC section 630.1(A)
= 22.5A - the reason I chose #10 wire per table 310.16 and according to NEC section 630.12(A) overcurrent protection shall not exceed 200% of the primary current rating of the welder, wich made me decide a 50A breaker should be safe. Does this seem accurate?
 
But does a 50a breaker protect #10 or a 30a receptical? - No....

See 240.4 B&D ('02 NEC) There is a little * on 310.16...
Also 210.3. 210.19
 
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e57 said:
But does a 50a breaker protect #10 or a 30a receptical? - No....

See 240.4 B&D ('02 NEC) There is a little * on 310.16...
Also 210.3. 210.19
Click to expand...

Yes it does. See 240.4(G). I think NEC 630 supercedes the other rules you mentioned.

He may be restricted to a single receptacle on an individual branch circuit. But other than that, #10 on a 50A breaker for a welder is very similar to the exceptions for motors and HVAC units.
 
Well thanks for the input. All of the welding receptacles I have installed in the past were in industrial settings and already designed and on blueprints/panel schedules with wire sizes and overcurrent protection predetermined by an engineer. So I had to do some investigating for this application. Just trying to keep it safe and wondering if I deciphered correctly.
 
e57 said:
But does a 50a breaker protect #10 or a 30a receptical? - No....
Click to expand...

Yes the 50 amp breaker will protect the conductors from short circuits and ground faults. :)

The welder will protect the conductors from overloads.
 
grady180 said:
(A)
= 22.5A - the reason I chose #10 wire per table 310.16 and according to NEC section 630.12(A) overcurrent protection shall not exceed 200% of the primary current rating of the welder, wich made me decide a 50A breaker should be safe. Does this seem accurate?
Click to expand...

I think to be technical and accurate, a 45 amp breaker would be the maximum allowed at 200%.With a duty cycle of 20%(50 x .45 = 22.5 x 200% = 45)
Rick
 
According to 630-12 (a )
Each welder shall have overcurrent protection rated or set at not more than 200 % of the rated primary current of the welder. The primary current of this welder is 50A. So does'nt that mean I could actually use a 100A breaker.
Not that I would because 630-12 states that if unneceaary opening of the overcurrent device occurs, the next higher standard rating or setting shall be permitted.
 
grady180 said:
So does'nt that mean I could actually use a 100A breaker.
Click to expand...
Bob has it right at 50 amps, i always thought it was 200 % at the duty cycle amps.

If you did use the 100amp fuses, then you would have to bump up to a wire that is rated for 50 amps.The 200 % is mostly used when your tapping off a feeder such as a bussway.With your welder,if the buss was rated at 200 amps and you set a buss tap fused disconnect,the max fuse would be 100 amps if you used a wire rated for 50 amps.But when using a single circuit, the breaker feeding the welder is limited to the rating of the welder and surprisingly,12 awg wire would be allowed.
Rick
 
Yes ,the wire size threw me off, from what I've learned in the past the welders seem to be a different issue. Good stuff to know! Thanks again for all the input on this subject.
 
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