Need a little help Wiring

[josh930]

I just got a Miller 330st Aircrafter stick/tig welder and need a little help setting up the electric. Its 300 amperes, 32 volts at 60% duty cycle. I want to set it up for the 230v power input. I just need to know what size wire to run out to my garage(50ft), what size breaker to use, and what size extention cord to use (I'm not sure if it has to be the same size as the one I run from the main box to the garage)(50ft).

I'm terrible at figuring out electric. If anyone has any web sites to read about electric that would help out too. Thanks and I appreciate the help, josh

[awright]

The first thing to do is download the manual from Miller if you don't have a hard copy. (http://www.millerwelds.com/om/o351h_mil.pdf).

The second thing to do is read the page (page 9) describing the input power wiring requirements. It says the input current at rated output on 230 volt supply is 92 amps. They suggest a circuit breaker of 138 to 184 amps rating. They recommend input power conductors of 4 AWG for conductor length not exceeding 137 feet, and grounding conductor size of 6 AWG.

So, that's what you need to achieve rated output and remain legal under the NEC.

The output rating (300 amps, 32 volts, 60% duty cycle) would give a clue regarding the required input conductors, but why estimate and guess when they give you exactly the information you need in the manual. They even show an illustration showing how to wire it up.

Now, if you don't like what they recommend and you think you don't need to provide for rated output, the next thing to do is wait for MAC072 to take notice of this post and advise you on alternatives.

Good luck.

awright

[awright]

Oh, yeah. You mentioned an extension cord. You are not going to have an easy time finding a connector capable of handling the rated current of this machine. Additionally, a properly rated cable of any significant length is not something you will be able to wind up by hand and throw over your shoulder.

Since your machine is HEAVY (750 poinds), you are not going to be wheeling it around your shop much so I recommend hard wiring it in to a properly rated junction box and/or disconnect switch. I had my eye out for one of those large industrial connectors rated at 90 amps for my machine and never found one (at least in surplus). Connectors rated for your welder input current must exist, but I think you'd pay a fortune and end up with a connector MUCH larger than a junction box.

I ended up hard wiring my welder and never regretted it. Since I'd need a fork lift to move it anyway, disconnecting the welder from the junction box would be no big extra effort. I haven't moved it in 30 years and probably never will.

awright

[runchman]

As someone who has done a lot of his own electrical work, I'd have an electrician do this installation.

Working with number 4 wire is NOT going to be fun at all!

Just my 2 cents.

[MAC702]

...Now, if you don't like what they recommend and you think you don't need to provide for rated output, the next thing to do is wait for MAC702 to take notice of this post and advise you on alternatives....
If the manual is recommending #4 conductors, they are already figuring in the derating for duty cycle. Go exactly with the manual's recommendations for this machine. Awright is steering you aright.

This type of machine would typically be next to a surface-mounted disconnect or panel and hardwired to the breaker, and this would also be my recommendation.

This isn't exactly a garage-type machine...

[Birken Vogt]

Sounds like you would like to have at least 200A service to the garage to provide plenty of headroom for other stuff which means 4/0 aluminum or 2/0 copper but it probably isn't absolutely necessary and may be precluded by the amount of service you have to your house. What service does your house have?

Birken

[MAC702]

This sounds like a detached garage, yes? If so, does it have any other power circuits already run to it? Any at all?

[josh930]

It is a detached garage. Theres not really anything running to the garage, plus its only temporary that I'd be using it there. I'd like to beable to pick it up and leave with most of my wire easy to access.

As of right now I'd like to run from the main panel(200A) to an outlet close to the garage(but still in the house) and run an extension cord from the outlet to the garage or just outside the garage where I'll be doing most of my welding. I have the welder on a cart with wheels so I can move it(which is in no means easy).

I will probably never use the full output range of the welder. I'll need enough juice to run a 5/32 electrode stick and for some tig. So is there anyway to hook this up without using all the juice that its intended for? I'm no electrician but I'm trying to learn as well as save a little money. Thanks for your help so far. :-)

[runchman]

There would be nothing wrong, from a safety standpoint anyway, of running, say, a 40 amp 220v circuit to your garage with the proper size wire and breaker, just to try the thing out.

I know nothing about this welder, maybe that won't even allow you to turn the thing on, I don't know.

But let's figure that 92 amps on the supply side gives you 300 amps on the output (as someone stated). Then (ballpark):

46 amps supply side gives 150 amps output

23 amps supply gives 75 amps out

I'd be inclined to wire up something like a 40 amp circuit with #8 wire. This is something that you can manage on your own without going nuts on a zillion amp circuit.

Sure you won't get full output, but do you need 300 amps? You might find that a 40amp circuit is fine and you never trip the breaker. Or you might not, I don't know.

This would at least get you welding without breaking the bank putting in the 'correct' 1xx amp circuit.

Just remember that the breaker needs to be sized no 'larger' than the wire, and you're safe. Where is the sweet spot that the welder works for your needs w/o putting in the giant full-output circuit, who knows.

OR, rationalize that you've bought a nice machine, pay an electrician to put in the correct service, and be done screwing with it forever. There IS something to be said for that approach!

- John

[josh930]

OK, so with that being said I feel I have 2 options. Which do you feel is better..

1 - Is it possible to hard wire the the 4-3 wire that is recommended with this machine but run a 60A breaker from the main panel(200A) and dont go beyond the breakers tripping point.

OR..

2 - Should/Can I hardwire 4-3 to the machine(which is recommended). Run a 140A breaker(which is recommended). And Run it off the main panel of the house? Now my only question with this setup is will the main breaker going to handle the welder(running a 5/32 electrode) plus run the houses power supply(200A) ok without tripping the main breaker? I will only be running enough juice to power the machine to run a 5/32 electrode. So it shouldnt cause a problem correct? The only way I would come close to tripping the main breaker is if I cranked up all the way, right?

[denrep]

“1 - Is it possible to hard wire the the 4-3 wire that is recommended with this machine but run a 60A breaker from the main panel(200A) and dont go beyond the breakers tripping point.”

1A- Yes you can use an undersize breaker with #4 wire but it will be difficult to connect 4 awg to a 60 amp breaker in a "workman like" manner. Add a sub-panel for this heavy work.

“2 - Should/Can I hardwire 4-3 to the machine(which is recommended). Run a 140A breaker(which is recommended). And Run it off the main panel of the house? Now my only question with this setup is will the main breaker going to handle the welder(running a 5/32 electrode) plus run the houses power supply(200A) ok without tripping the main breaker? I will only be running enough juice to power the machine to run a 5/32 electrode. So it shouldnt cause a problem correct? The only way I would come close to tripping the main breaker is if I cranked up all the way, right?”


2A- Welder load (ie: 92amps max ) + house load (ie:108 amps) = (200 amps) total must be no greater than 200 amps.

In this scenario you would have 108 amps “surplus” power for the home while welding at maximum output. Turn off the hot tub and AC you probably will be fine. Again, sub-panel the 140a breaker.

You want - and code probably requires a disconnect within eyesight and easy access of the welder (same building).

There are a few other details. Distance, ambient temperature, type of conductor, number in raceway etc.

I say bury it in plastic conduit if you can.

[Birken Vogt]

“1 - Is it possible to hard wire the the 4-3 wire that is recommended with this machine but run a 60A breaker from the main panel(200A) and dont go beyond the breakers tripping point.”

1A- Yes you can use an undersize breaker with #4 wire but it will be difficult to connect 4 awg to a 60 amp breaker in a "workman like" manner. Add a sub-panel for this heavy work.

Just a nit pick but #4 wire should go in a 60A breaker just fine; many applications require it because of voltage drop.

Birken

[Birken Vogt]

To the original poster:

I would not wire it with any less than what is required. Here is why.

The wire sizing calculations in article 630 (welders) and all wire sizing in general are done that way to protect the wire from overheating and catching on fire. The circuit breaker at the head end is not there to protect the wire from overheating. Rather, it is to open in case of a dead short or other major fault.

The wire is protected from overheating by the proper calculations of the person installing it, and the safety devices in the appliance using the power. The welder will trip out its safety because of overheating (of the welder itself) before the wires in the supply circuit will overheat, if the calculations have been done correctly. This because the NEC allows significantly undersized wires on welders due to their low duty cycle usually.

If you put undersized wire in, you will not have the benefit of this protection any more, regardless of the size of breaker on the line.

If you put in an undersized breaker, you will be pushing the limits of the breaker itself. The breaker will get hot and possibly trip if you are running near its limit. In my experience once a breaker has tripped under load it can no longer really be trusted and it will often get weaker as it continues to trip under load until it needs to be replaced.

My advice is if you don't think you will be running it full tilt, wire it at the minimum the NEC will allow, but at least stay within the code. This means a 125A breaker to stay within the 80% load of the breaker rating, and #6 copper or #4 aluminum (at the very least) but they specified #4 copper for a reason, and most of the cost is in the labor vs the materials anyway, plus those calcs don't figure voltage drop, only wire heating.

You should go ahead and get the bigger breaker, because it doesn't really matter what size you use; anything up to 190A will protect the wire from a short just fine.

Birken

[Sandy]

1 - Is it possible to hard wire the the 4-3 wire that is recommended with this machine but run a 60A breaker from the main panel(200A) and dont go beyond the breakers tripping point.

That option is out. Breakers are not intended for current nor load control. They are intended for fault interruption. Nor is it intended that the operator be an integral part of the current control or fault interruption.

These guys are all giving good advice. What they/we have been tip-toeing around is the fact that the NEC has already made all the allowable concessions for welders and still maintain an acceptable degree of safety, ie., saving money is not in the eqaution anywhere.

:)

[Bruce]

I gotta go with Sandy on this one. If you can't set it up right, pay someone to do it! Otherwise it could be a recipe for disaster!

[denrep]

To add the branch circuit, I’ll bet that your friendly local wrecking contractor has a pile of newer breakers and matching boxes for probably under $50.00, ready to mount. If you buddy up and offer to weld up some of the equipment that they constantly break and wear you’re probably going to get some “fresh pulled” wire too. He's busy and under a lot of pressure, you gotta catch him at the right time!

[runchman]

One last thought...

Someone said this thing weighs 750 pounds? It's probably much more likely then that you are going to want to bring the work to it, rather than bring it to the work.

I'd figure out where you want it to sit for the next xx years, call up an electrican, point him to it and ask him to make it happen. Come back to the welder a day later and start using the beast.

I recently built a deck and could have shingled it myself. Would have saved some money, but it would have been a pain - I had 6 skylights to go around. So I had a roofer do it; went to work in the morning, came home that night and I had a roof.

Definitely worth the cost, and I think your circuit is in the same boat! This isn't just a 14-gauge 15-amp circuit in your basement, this is some heavy gauge sh*t. Don't mess with it!

[awright]

Re. Denrep's suggestion: Just do NOT install salvaged FPE equipment.

awright

[josh930]

Thanks for all the great advice. I'm not trying at all to to go the cheap route as it will probably cost me more in the long run. It's more along the lines that I'm trying to learn what each component will do if matched up incorrectly and what not to do and why. I was worried that the bigger breaker would draw too much current off the main panel and trip off the main breaker(which sandy posted earlier is incorrect). I thought the 60 amp breaker would some how control it a little more. But after reading your comments I can run a 140A breaker but just keep the juice down on the machine and run everything according to the book. What I guess I should have posted after reading this is "how a breaker works" but I think I would have gotten bashed for asking a question like that. Thank you everyone and if I still have it wrong I'll give you my adress and you can come over and slap me :dizzy:

[Birken Vogt]

I'm not an electrician by trade but I do a fair bit of electrical work anyway. I find that the heavy duty stuff is often easier in a way, either a 150A or a 15A circuit can start a fire that burns your house just as well so just do it right either way. Know your code book and keep it handy.

Birken

[josh930]

I'm not an electrician by trade but I do a fair bit of electrical work anyway. I find that the heavy duty stuff is often easier in a way, either a 150A or a 15A circuit can start a fire that burns your house just as well so just do it right either way. Know your code book and keep it handy.

Birken

Thanks for the tip. I will do that:)