Why is my dryer's 220v plug different from my welder's 220v plug?

http://members.cox.net/michaelshaffer/wtf.jpg
Is it safe to plug the welder into this recepticle, will it even fit?
Thanks Mike
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Michael Shaffer wrote:

It won't fit.
The dryer plug is a 30A 220V with a full sized grounded wire that is also used as a neutral (NEMA 10-30). The welder looks like some kind of 277V plug, but I'm not sure which one (NEMA 7-something). But welders are notorious for being wired with whatever big plug is available. It might work if you replace the plug on the welder, but you'll have to look at the welder's electrical specs.
Best regards, Bob
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[Old fashioned 3-wire dryer connects. These days they're 15-30 four prong]
A "proper" 30A 240V receptacle will be a 6-30R. Coffin style "welder receptacles" available from DIY and hardware stores are 6-30R or their 50A cousins 6-50R. See link below for drawings and applications.

People might find pages 8 and 9 helpful:
http://www.hubbell-wiring.com/library/Section-W.pdf
Home-owner/hobby duty welders plate-rated at 50A will often appear to work "just fine" on 30A circuits.
This is because a 40A draw, say, on a 30A circuit will take a fair length of time to trip the breaker. Your "welding habits" may have a duty cycle low enough that it will never trip the breaker.
[One friend referred to his welder circuit as the "3/4 rod circuit". He could run 3/4 of a rod as a single bead before the breaker goes...]
Is it adviseable to do this? No. Because repeatedly stressing the circuit like this may cause connections to eventually fail. Or the breaker too if it pops more than a few times - they're not rated for large numbers of activations.
Against code as well.
_Especially_ bad if you want to use the welder a lot.
The OP needs to check the welder to find out what it _needs_ before assuming that any given supply circuit will work.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Chris Lewis wrote:

That's why I told him to "look at the welder's electrical specs." Thanks for the hubbell link. I haven't seen all that information in one place before.
If the voltage is right (that 277V plus is kind of weird), the welder and the breaker will be just fine on a 30A circuit if you run it at low to medium amperages. The amount of current drawn by the welder is proportional to the welding current. If OP wants to weld anything thicker than about 3/8" or use fast-fill rods (like E7024), he should wire a proper 50A circuit.
Tripping the breaker during a weld is kind of frustrating. Having the dryer start tripping the breaker down-the-road because you wore out the breaker by repeatedly overheating it will get your wife pissed at you. I'm not sure which is worse (although the latter is certainly more dangerous :-)
Best regards, Bob
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I was just trying to re-emphasize what you said.

It was getting frustrating because the NEC (and CEC) with their diagrams aren't online, so I spent some time googling for a decent chart of them _all_. That link was the result.

Yes, it is a bit wierd, but suggestive that it was done by a industrial electrician as-per-the "okay to use wierd plugs if they can't get confused" rule that _we_ have, and volts500 ranted on about. Or an out-and-out hack by someone who just happened to have a few wierd receptacles in their parts box.
It's more _likely_ that the welder is a 240V unit intead of 277V, but not guaranteed, so he MUST check the plate to be sure.

If he's starting from scratch, best to do it 50A. The cost differential ain't much.
I've been thinking about getting a welder myself. I have some 6-30R circuits installed in perfect places for using one. I'd probably use them at first, and if I started tripping the breaker, or someone got nervous, I'd string a 50A circuit.

I'd be more worried about damaging the breaker so it _doesn't_ trip. Ie: FPE "no blows". Breakers aren't designed to be activated that often. They also not designed to be used as power switches for motors. Regular duty breakers have a relatively short lifetime in terms of tripping. Exceeding that is asking for trouble. Potentially _big_ trouble.
So, if the user finds themselves tripping the breaker under "normal conditions", they should consider converting the circuit over to what the plate requires.

Oh, I hear yah ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Michael Shaffer wrote:

dryer.. that will not work for the welder so you need a higher amp. line to run the welder.....
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I run my Craftsman AC welder from my dryer plug, no problem. As I recall the welder goes up to at least 90 amps whereas the dryer line is fused for 30 amps, but its working, don't ask me why.

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Marty wrote:

The welder is a step-down transformer that reduces the voltage and increases the current. It converts the high voltage and moderate current into moderate-to-low voltage at high current. I have a 230A welder that I believe draws 48A maximum. I don't think I've ever used it at full power, so it would probably work OK plugged into a 30A dryer outlet.
(the processor chip in your computer probably draws over 20A at some low voltage, even though the computer draws less than 3A at 117V)
Bob
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Nevermind, answered on another newsgroup.. different amperage ratings
Michael Shaffer wrote:

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The dryer requires both 240V and 120V but the welder required 240V only.
The dryer plug you have is an old, now obsolete, 120/240V 30A with NO grounding connection, only 2 hot leads for 240V and a neutral (grounded -- NOT the same as grounding!), the neutral is the L shaped one. The old obsolete range plugs (120/240 50A) have a straight neutral not L shaped. The dryer plug may or may not be upgradeable, depending if the cable has a ground wire in it in addition to the 3 current carrying wires.
Your welder requires a plug w/ 2 hots (for 240V) and a grounding terminal (U shaped). A new style dryer (or range) plug has 4 terminals not 3, in which case, IF the amperage rating was high enough, an adaptor cord (with the neutral not connected could be made) but he right way is to use a straight 240V grounded recepticle. IIRC a 30A 240V looks like an oversized 120V/15A and a 240V/50A is the same size as the 30A but with coplaner blades not parallel.

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