Help with wiring for a MM180 Auto-set

[reefera4m]

After reading several similar threads I;m still unclear on a couple of issues

.According to my Millermatic 180 Auto-set welder Electrical Service Guide:

Input voltage - 230
Input ampheres at rated output - 21.7
Max recommended standard fuse in ampheres (normal operating fuse) 30
(Note circuit breaker with time-current curves comparable to recommended fuse)

Min Input conductorsize in AWG - 14
Min Grounding Conductor AWG 14

However the machine came with a 3-prong/50 amp plug (6-50??).

I'm wiring my new shop and, according to an electrician, to use the 3-prong/50 amp plug I will need a 50 amp breaker amd 6 guage wire to a 50 amp 6-50 receptical. The expense is bad enough but the 50 amp circuit breaker is way over the recommeded 30 amp.

I've used an adapter extension cord from my 30 amp dryer outlet to the welder and it works just fine ( 30 amp plug on one end for the dryer and a 50 amp receptical for the welder plug - 6 guage copper wire) but this won't pass the electrical inspection.

Questions - is it possible to replace the welders plug/pigtail with a 30 amp plug/pigtail and use a 30 amp circuit breaker? Given the short run from the pane to the outlet I could probably use #10 or #8 wire.

It would seem that a 30 amp breaker would provide a better margin of safety that a 50 amp breaker (the 30 amp would trip sooner in the event of a problem), particularly since the input amps are only 21.7.

Advice or suggestion - keep in mind I'm in the rough-in wiring phase and this is the last circuit before inspection.

[Broccoli1]

Miller's manuals are confoosing in the Electrical section.

You are fine with using a 50amp Breaker for this machine and since it is such a short run just have your Sparky use the #6 wire and you'll be set for any growth.

This will allow you to purchase a MM252 or 350p


Miller provides the MINIMUM guidelines for a Circuit for this machine.

Note the 14g wire- thus the max breaker recommended is 30amps

This is due to the Duty cycle of the machine (I believe it is Art. 630 of the Nec)

[reefera4m]

I emailed Miller with my question and here is the answer I received:

Quote

"We actually recommend a 30 amp breaker for the MM180. It has a 50 amp style plug on it in an effort to keep the plugs on our machines consistent. You could wire a 50 amp receptical to your 30 amp service, the plug will just be oversized for the application. We do not make any off the shelf pigtails to go from the 50 amp style plug to the 30 amp style plug, you would half to make one"

David Miller
Service Technician


Since the NEC ususally requires that a 50 amp receptical has a corresponding 50 amp circuit breaker and 6 gauge wires, I call the electrical inspection department of Labor & Industries (State of Washington) and spoke directly with an inspector (department head). He said that I could used the 50 amp receptical with a 30 amp circuit breaker and #10 wire but that I need to label the circuit at the subpanel as 'Welder Only'.

Makes sense to me.

[Broccoli1]

Yeah, you can do that too.