Welder Attachment Plug

[JES2727]

I am installing a circuit for a welder. The supply voltage is 208V, single phase. The input amperage is 91. The manufacturer recommends input conductors of #6. They also recommend OCPD of 150 A. I've read article 630 and all of the recommendations comply. So I will pull in #4's rather than 6's because of the length, and protect it at 150 amps. I'll get some #6 SO cord to connect to the welder. What should the attachment plug be rated? Should it be rated for the load (91 amps), the wire ampacity ( 60 amps) or the OCPD ( 150 amps)? I intend to connect it with a 60 amp plug, but only because " that's the way we always do it..."

 

[BenS]

Not that it is right.. but we have been using a 50 amp plug at 208 on a variety of welders successfully for as long as anyone can recall. What kind of machine is it?

 

[JES2727]

It's a Miller Shopmaster 300.....

 

[BenS]

Thats a big one... why can't it just be hardwired? If not an option, go with 100amp plug minimum.

 

[JES2727]

go with 100amp plug minimum.

Why a 100 amp plug? What criteria is used for determining the rating of attachment plugs?

 

[BenS]

Actually, you might want to check your manual again for that welder.
If I am reading it right your max amps is 105, and you need 4AWG.
http://www.millerwelds.com/om/o322a_mil.pdf
That is a beast of a machine!

 

[JES2727]

Thanks for the input BenS. The unit I'm connecting is a bit older. I've been looking in this manual: http://www.millerwelds.com/om/o318d_mil.pdf
The info in the electrical chart on page 15 is essentially the same as the info on page 17 of the manual you pointed me to. I still see 91 amps at 230V, and 105 amps at 200V. My source voltage is about 213V, so I'll split the difference and call it 98.
I still don't know how to rate the plug and receptacle.....

 

[LJSMITH1]

If this welder is not intended to be portable (meaning no casters on it), then I would hardwire it to a wall mounted, fused disconnect. For the number of times it may need to move, it would be easier to remove and move the disconnect.