MM175 on 40amp breaker

[4speed]

Hey guys, I'm going to be ordering a MM175 this monday!!! CANT WAIT!!
anyways..here at mi casa we have a 230volt line run on what looks like 6-3 wire on a 40 amp breaker, it was from a oven that we no longer have..so its getting comandeered for the welder...
will this be good enough for the amp draw of the welder? I've seen were they recommend a 50 amp breaker...whats your opinion?

[Zrexxer]

Miller does not recommend a 50A breaker for the MM175, they recommend a 20A. From the owner's manual at http://www.millerwelds.com/om/o1324g_mil.pdf:

[4speed]

whats all this talk about 50 amp breakers then?
so 40 amp would FRY the welder before it tripped?

[James D. Clark]

No, the 40 amp breaker won't fry your MM175. The welder has it's own internal breaker for overlaods which is set to 20 amp. The 40 amp breaker protects the line to the wall outlet. The #6-3 line can handle it.

[Zrexxer]

Sigh... this is the subject of great debate here, and I don't want to get the controversy started again, but the breaker is there to protect the wiring, not what's plugged into it.

[Sberry]

Zrexxer, this is a sore spot in the manuals for these class machines especially since they are marketed towards the DIY thing. The ratings are as clear as mud written by engineer types for electricians well versed in code. Notice the minimum wire size. and the ground size. This machine has a number 12 cord. The 20A breaker rating is when the minimum wire size is used. If one used a number 12 wire it could legally use a 50A breaker. But, the recept that is used is NEMA rated for a 10 thru a number 4 wire which really means the wire should be a 10 to feed the recept. When I wire for this class it is a 10/30 circuit but his existing wire and breaker are fine and legal for this setup with a recept change. The breaker isnt designed to protect anything in this type of circuit except short circuit.

[4speed]

so....should i just replace the breaker at the breaker box with a 20 amp breaker...? I'm a noob when it comes to things like this..

[Zrexxer]

Reading my post again I probably gave the wrong impression Cary, I didn't mean that Miller discouraged the use of a 50A, but rather that they didn't require a 50A. What I meant was given the right configuration (service/breaker/receptacle) it could be run on as small as a 20. I could have worded that better.

[4speed]

so basically the breaker in the house is just there to protect the house and wiring...
am i getting it right that the internal breaker in the welder itself is actually what is going to be protecting the welder.... correct?.

[TOMWELDS]

A note: is the old oven cable aluminum? it would still be plenty for 20amp but was just wondering.

[James D. Clark]

so....should i just replace the breaker at the breaker box with a 20 amp breaker...? I'm a noob when it comes to things like this..

I think what you will need to do is replace the wall receptacle to a NEMA 6-50 R and change the wire to the center lug in the outlet back at the breaker panel from the neutral bus to the ground bus. Your MM175 as well as other similar welders come with a cord set with the NEMA 6-50 P plug. The center (between and not in line) pin (it's U shaped) is the ground pin. The other two pins are flat blade connectors that are parallel. Your present outlet has the lugs angled and the welder plug will not fit it.

Search this site for pictures and postings about NEMA 6-50 plugs and cords, etc. There was something only a couple of days ago. About where to find that outlet and other matters. If you have #6 wire your breaker is ok.

If you aren't comfortable working with the electrical panel or wiring the outlet, get an electrician. They work for less than undertakers.

[4speed]

im not sure if its aluminum or not, its Type SE 300volt XHHW (3 CDRS 6 AL)
maybe the AL denotes aluminum, but im not up on electrician speak..

[TOMWELDS]

Yup..SE=service entrance cable. AL=aluminum. You could use it, even though the ground is a bare aluminum wire. Cant you run a 12/2 or 10/2? The other problem is you will have to 'tail' the wire to a copper #12. which means a splice box and aluminum split bolt connectors then running to the receptacle box. It'll look like **** to say the least.

[James D. Clark]

There is only one approved method for ending aluminum cable to connect it to outlets and fixtures. It's called the Copalum Crimp Method which requires special parts and tools. Could be your wiring already has the correct terminations for the aluminum cable.

[Sberry]

Why would he have to splice anything? Just put the new recept on, replace the old with the new and be done. If this is a range circuit it probably comes from main entrance panel so the ground is fine where its at in the panel.