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Old 12-03-2006, 01:54 PM   #1
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Do I have a 30 amp or 70 amp welder. And help wireing it.


I have a miller welder I'm trying to wire up. On the front is says 30 amps. On the back of the welder it says 70 amperes. Which one is it?

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Old 12-03-2006, 02:05 PM   #2
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Do I have a 30 amp or 70 amp welder. And help wireing it.


What's the model number of the welder, and we'll help you sort it out.

Most often, the input power from 120 or 240 will be much lower in amperage than the output power. 30 amps at 120 volts would sound right, since your output from a MIG welder is normally operated between 16 and 18 volts.

Post the model number, and we'll sort it out.

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Old 12-03-2006, 02:11 PM   #3
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Do I have a 30 amp or 70 amp welder. And help wireing it.


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Originally Posted by mdshunk View Post
What's the model number of the welder, and we'll help you sort it out.

Most often, the input power from 120 or 240 will be much lower in amperage than the output power. 30 amps at 120 volts would sound right, since your output from a MIG welder is normally operated between 16 and 18 volts.

Post the model number, and we'll sort it out.
It's a 220 stick welder

I don't see a model number. It is a Miller Thunderbolt XL. Here are the specs from the manual.
http://img239.imageshack.us/img239/4772/welderfu3.jpg



Would Nema50 recepticals be acceptable?
What gauge wire should I use to my receptical? I have a 4-3 exension cord that came with the welder which I'm sure is overkill but for free I'm going to use it. Should I just wire the receptical with 4-3? It's a very short run so I'm not overly concerned about the price.
What is the smallest gauge wire I could get away with on an extension cord?
What breaker should I install? The guy had it hardwired into a 100amp which seems to high to me.


Link to manual:
http://www.millerwelds.com/om/o316s_mil.pdf

Last edited by Tmb9862; 12-03-2006 at 02:15 PM.
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Old 12-03-2006, 02:23 PM   #4
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Do I have a 30 amp or 70 amp welder. And help wireing it.


I see the manual calls for Nema 6-50 p&r recepticals. Does that mean 6 gauge wire?
The cord supplied with the welder is 8-3.
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Old 12-03-2006, 02:55 PM   #5
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Do I have a 30 amp or 70 amp welder. And help wireing it.


No, 6-50 is the NEMA number. The "6" just denotes "250v, 3-wire".
http://www.leviton.com/sections/techsupp/nema.htm

The instructions are pretty clear. Up to 75' branch circuit you can use #8cu on a 90 amp breaker. This is using the special conditions allowed for a welder in the NEC. For a residential application I do NOT like to use this. Someone can come along later and mistake the receptacle for a "regular" 50 amp receptacle.
In fact I am surprised they say to use a 50 amp receptacle on a 90 amp circuit since this is not allowed under the NEC.

If this were my installation I would use #2cu or #4cu to a 100 amp disconnect and hard wire the unit. I would label the disconnect "WELDER USE ONLY". I would not be comfortable with a 50 amp receptacle on a 90 amp circuit.
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Old 12-03-2006, 03:06 PM   #6
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Do I have a 30 amp or 70 amp welder. And help wireing it.


This is a case where the manufacturer's documentation are in conflict with the NEC. This surprises me very much, from a company like Miller Electric. They are famously on top of their game. I, too, would push for this unit to be hardwired from a disconnect. That said, it is very common for a stick welder to have a 50 amp receptacle on a 70 or 80 amp breaker. I'd do that, unless you intend to be welding long beads on very thick plate. In that case, do the 100 amp disco.

Last edited by mdshunk; 12-03-2006 at 03:10 PM.
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Old 12-03-2006, 03:24 PM   #7
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Do I have a 30 amp or 70 amp welder. And help wireing it.


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No, 6-50 is the NEMA number. The "6" just denotes "250v, 3-wire".
http://www.leviton.com/sections/techsupp/nema.htm

The instructions are pretty clear. Up to 75' branch circuit you can use #8cu on a 90 amp breaker. This is using the special conditions allowed for a welder in the NEC. For a residential application I do NOT like to use this. Someone can come along later and mistake the receptacle for a "regular" 50 amp receptacle.
In fact I am surprised they say to use a 50 amp receptacle on a 90 amp circuit since this is not allowed under the NEC.

If this were my installation I would use #2cu or #4cu to a 100 amp disconnect and hard wire the unit. I would label the disconnect "WELDER USE ONLY". I would not be comfortable with a 50 amp receptacle on a 90 amp circuit.
Thank you for the help.

Do you mean hardwire the welder to the disconnect? That isn't an option as the welder is stored in a detached garage and the plug will be in the basement. The welder also has to move between two driveways and the garage requiring a 120ft or so extension cord if hardwired.

I'm not worried about anyone else useing the plug. It's going to be located in the basement and their really isn't any other 220v equipment in the house that could be plugged into it especially not somthing with a 50 amp plug. That and clearly labeling the outlet should be fine.

So basically going that route I'd be fine running 6-3 (I know it only has to be *) to a Nema-50R receptical. Then useing my 4-3 extension cord.



What would be the best way to connect the extension cord to the welder besides wireing the cord right to the welder? The previous owner just used wire caps which can't be a good idea. Can I use a box and the copper bolt connectors? Or do I really have to get the male/female cord ends?

Last edited by Tmb9862; 12-03-2006 at 03:26 PM.
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Old 12-03-2006, 07:29 PM   #8
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Do I have a 30 amp or 70 amp welder. And help wireing it.


It seems to me that unless you have one of the welders noted in the footnotes of the Miller label, then your "rated" input amps will be 47.5. Note this is not "max" input amps. Rated is the amp draw it will pull when operating at the design useable duty cycle. (i.e. how many minutes out of 10 where it can weld without tripping the breaker or causing it to shut down on internal overload protection). It would be best to supply it with enough for max output, but since welders (especially at home) are intermittent loads rather than constant loads, it is fine to supply with a circuit adequate for its "rated" input amps. That said, nearly every welder out there, and historically, come with a NEMA 6-50P plug on its cord. Just install a NEMA 6-50R receptacle, with #6 copper wire, and a 50 double pole breaker (or even a 60 amp), and you're good to go, with no special labeling or future concerns for the receptacle as it will be properly wired and protected. If you think you will be really running that welder wide open a lot, you may want to consider upsizing the breaker and wire feeding the receptacle. I don't think its a problem having a 6-50R receptacle (which is considered the standard welder recep and often is labeled as such on mfr boxes that they come in) on a circuit with larger breaker and wires because welder manufacturers know their equipment is not going to be operated as a continuous duty load. This gives some forgivness in allowing it to be supplied by smaller wire than a continuous duty load would need. I don't know if larger wire, say #4 copper, can land on a 6-50R receptacle. I imagine it would. Maybe one of the electrical pros here can answer that. As far as what to have on the welder.....put a 6-50P plug on the cord....the green wire in the cord will connect to the round grounding pin in the plug, the other two will go to the flat blades. You'll probably never have a problem if you use a 6-50 plugs/receps, #6 copper, and a 50 or 60 amp breaker. As far as extension cord, didn't you say you have a big honking #4 cord already? If you want a smaller one, I would make one up using #8 copper.....3 conductors (2 hot leads and a grounding conductor). Only if it needs to be very very long would you need a larger gauge ext. cord to guard against voltge drop. There are online calculators where you can have the voltage drop calculated. It would be best to not have more than a 5% drop on the ext cord. So the idea is your welder cord will have a 6-50 plug, your extension cord will have 6-50 plug and recep, and your receptacle will be 6-50R. Done deal, and your machine and power supply are all standardized welder configuration.

Last edited by cebola; 12-03-2006 at 09:20 PM.
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Old 12-04-2006, 07:49 AM   #9
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Do I have a 30 amp or 70 amp welder. And help wireing it.


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Originally Posted by cebola View Post
It seems to me that unless you have one of the welders noted in the footnotes of the Miller label, then your "rated" input amps will be 47.5. Note this is not "max" input amps. Rated is the amp draw it will pull when operating at the design useable duty cycle. (i.e. how many minutes out of 10 where it can weld without tripping the breaker or causing it to shut down on internal overload protection). It would be best to supply it with enough for max output, but since welders (especially at home) are intermittent loads rather than constant loads, it is fine to supply with a circuit adequate for its "rated" input amps. That said, nearly every welder out there, and historically, come with a NEMA 6-50P plug on its cord. Just install a NEMA 6-50R receptacle, with #6 copper wire, and a 50 double pole breaker (or even a 60 amp), and you're good to go, with no special labeling or future concerns for the receptacle as it will be properly wired and protected. If you think you will be really running that welder wide open a lot, you may want to consider upsizing the breaker and wire feeding the receptacle. I don't think its a problem having a 6-50R receptacle (which is considered the standard welder recep and often is labeled as such on mfr boxes that they come in) on a circuit with larger breaker and wires because welder manufacturers know their equipment is not going to be operated as a continuous duty load. This gives some forgivness in allowing it to be supplied by smaller wire than a continuous duty load would need. I don't know if larger wire, say #4 copper, can land on a 6-50R receptacle. I imagine it would. Maybe one of the electrical pros here can answer that. As far as what to have on the welder.....put a 6-50P plug on the cord....the green wire in the cord will connect to the round grounding pin in the plug, the other two will go to the flat blades. You'll probably never have a problem if you use a 6-50 plugs/receps, #6 copper, and a 50 or 60 amp breaker. As far as extension cord, didn't you say you have a big honking #4 cord already? If you want a smaller one, I would make one up using #8 copper.....3 conductors (2 hot leads and a grounding conductor). Only if it needs to be very very long would you need a larger gauge ext. cord to guard against voltge drop. There are online calculators where you can have the voltage drop calculated. It would be best to not have more than a 5% drop on the ext cord. So the idea is your welder cord will have a 6-50 plug, your extension cord will have 6-50 plug and recep, and your receptacle will be 6-50R. Done deal, and your machine and power supply are all standardized welder configuration.
Well the only thing I'm a bit confused about now is I have two differant recommendations for the breaker size. I realize they list 90 amps as the max. If I put a 50amp breaker in will I be tripping it running the welder at full power for its entire duty cycle (not that it will happen often if ever).

I'm going to run 6-3 out of the box to a 6-50R receptical.
Then make an extension cord out of the 40 ft length of 4-3 wire I have with 6-50P and 6-50R ends. Then put a 6-50P end on my welders cord.

Now if I need more cord than I have I could just remove my welders six foot cord, wire a 35ft cord right into the welder and put a 6-50P end on. In doing that would it be better to wire my 4-3 cord right into it and use the 8 gauge wire for an extension cord or wire an 8-3 cord right into it and use the 4-3 for an extension cord. Basically the cord is either going to step up or step down, which one is better or does it make no differance? It seems to me it would be better to have it step down (I know ideally it would stay the same) in terms of voltage drop.

Last edited by Tmb9862; 12-04-2006 at 07:52 AM.
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Old 12-04-2006, 01:54 PM   #10
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Do I have a 30 amp or 70 amp welder. And help wireing it.


I set it up just like I said.
6-3 to a Nema 50R receptical.

I put in a 50 amp breaker as I wasn't sure what to use. I welded up my plow and the breaker didn't trip so I suppose I'm alright.


Next question. Could I plug a comressor into this plug so long as it draws 50 amps or less? Or is the 6 gauge wire not enough to do that?
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Old 12-04-2006, 05:56 PM   #11
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Do I have a 30 amp or 70 amp welder. And help wireing it.


You could even go to a 60 amp breaker and be fine with the #6 wire feeding the receptacle, if you needed to. Depends on where you look it up, you will see 50 and 60 amp being the commonly stated continuous duty ampacity for #6 wire. To really cover all bases, an elect. contractor or electrician would look at the temp ratings of the devices and the wire insulation type, and look up the ampacity for #6 copper wire for the ambient temp in the area where the wire is located, but if you bought a modern receptacle and use THHN or THWN wire or cable like you probably did, you are all set unless this is located in a hot location where the ampacity would need to be derated (larger wire would be required). The beauty of making it a standard receptacle instead of derating the wire size for a dedicated welder recep, is that it is appropriate for other things as well. A kiln is a common high amp continuous duty load that would not be proper to power from a derated welder receptacle. It sounded like in your original description that the distance from your panel to the recep is short (?), so it would be easy if you ever decided to up the breaker and wire size if you started tripping the breaker. If you wire it for continuous load, you won't have to worry about it being a special purpose recep. Just keep the breaker size appropriate for the wire size.
It does not matter in what order the smaller and larger wire are in, as far as voltage drop with your ext. cord. If the machine came from Miller with a #8 cord, then as long as you stick with that size or larger on the machine, it doesn't matter if you decide to install a larger size cord on the machine. Just don't go smaller. My welder came with a 6' long cord which irritated me being short, because it meant I would nearly always be using an extension cord, so I opened the case very carefully, and replaced it with a 20-something foot cord and a 6-50 plug. And I bought cord with a temp rating on the isulation around the conductors that was higher than the original cord had. Hardly ever will need an ext. cord now. You might want to consider that, especially since your box is already pretty heavy....a few more # of cord won't hurt. Also make sure if you buy cord for the machine or to make an ext. cord, you get stranded wire, not solid. It needs flexibility.
Sure, you could put a 6-50P plug on your compressor and run it off that welder receptacle, as long as that source meets what the mfr of the compressor specifies on the nameplate. I assume you are talking a compressor that is also 240 volt, 1-phase AC input like your welder? Then look for what the full load amps needed is. Check the manual for the compressor, if you have it. I can't imagine it needing more than 50 amps unless it is a bigun. BUT....sometimes a piece of equipment will also specify a MAX limit on amps the source can supply....I think that has to do with limiting the amount of current that would be supplied in case of a fault....but the electrical pros can better comment on that. If your compressor also needs 240v, single-phase AC, and the full load amps is under 50, I would plug it in and go. Ideally the most load you should intentionally place on a circuit continuously would be 80% of the circuit's ampacity..... but a compressor may also have some allowance built in to the name plate rating for it being intermittent. I don't know if they are considered continuous loads.
Electrical pros?
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Old 12-04-2006, 07:30 PM   #12
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Do I have a 30 amp or 70 amp welder. And help wireing it.


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Electrical pros?
My opinion.... if you expect me to read that very long post, I'd need your address so that I can send you a bill for the time it took to read it.
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Old 12-04-2006, 07:44 PM   #13
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Do I have a 30 amp or 70 amp welder. And help wireing it.


ahhhhhh hahahahhahhahhahhahah!!!
I do like your sense of humor. Sorry I do get a little windy sometimes.
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Old 12-04-2006, 08:21 PM   #14
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Do I have a 30 amp or 70 amp welder. And help wireing it.


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Sorry I do get a little windy sometimes.
Nah. You just like to type.
Or maybe you have one of those voice recognition thingys.
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Old 12-04-2006, 08:25 PM   #15
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Wow. I got a response out of the two top electricians on the internet today, and no technical corrections to my posts. Now....there must be something in there that I goofed on?????

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