Input Amp Question

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what's everyone's feeling about running a machine on less input amps than called out by the machine?  I've got a lead on a cyber tig 300amp machine which needs 98amp input on a 230v circuit.  I only wired for a 60amp circuit and was only going to put a 50amp breaker on.  do I need to redo my circuit for a welder like this, or can I just run it at 1/2 power or less and be ok?  Obviously I'm not worried about my house or anything, the breaker takes care of that but will it be bad for the machine?Thanks Millermatic 135Syncrowave 250
Reply:The most power the TIG will draw is related to the breaker installed. In your case the limit would be 50 amps. Having wire rated to carry more current than the breaker will allow is not going to hurt a thing. You don’t want it the other way round, wire too small to carry a large current.
Reply:Yea, I know that which is why I have it installed the way I do.  Definitely would be suckey to burn my house down because the wire in my walls melted!  My concern is: is it bad for the machine to run with limited input amps?  I certainly dont want to break anything on a machine this old because I'd never be able to find parts to fix it.  Even if I did they would probably cost more than I plan on paying for the machine so it wouldn't be worth it.Last edited by mot krig; 03-31-2010 at 04:49 PM.Millermatic 135Syncrowave 250
Reply:Originally Posted by mot krig is it bad for the machine to run with limited input amps?
Reply:Sounds reasonable to me.  Had just read somewhere that it was bad to underpower machines like that.  Any opinions on whether I should even bother running a 300amp machine on a 50amp breaker?Millermatic 135Syncrowave 250
Reply:Note:  Some machines (like 'old school' big transformer machines) need the listed/recommended breaker just to fire up.  Some newer (inverter) machines are a bit easier on the amperage start-up surge and may or may not be able to run on a smaller breaker than 'recommended' if used at lower output amperages.Big old-school 300 amp transformer machine that says it draws 98 amps at rated output will most likely just instant-trip a 50 amp breaker on (attempted) start-up.  Double-check the manual.  If the machine says it will draw 98 amps at rated output, the manual -probably- says that you need a 120 amp breaker.  The manual probably also says something about the recommended/required input wiring size and max length.As to having too small a breaker for the machine, that aspect won't hurt the machine.  The breaker will just trip and then the machine is off.     But the wire diameter (gauge) and the length can affect a machine because of voltage drop over the wire length at the (attempted) amperage draw of the machine.  That can heat up the wires (fire!) or trip the breaker or burn out the machine.  None of which is really any good.RTFM and see what it says is needed/required/recommended.  But IIRC, the 300 amp machines on 230/240V power that say they draw 98 amps usually need a 100+ amp breaker and circuit (wire size) to run.  YMMV.  The best laid schemes ... Gang oft agley ...
Reply:Well like I said, I dont have it yet thus dont have the manual and haven't been able to get enough info from the guy to find the right manual online.  I'll look into it though and see what it says.  This is definitely a big 'ol transformer machine so if what you say is true, it probably will need the full 100amps to fire up.  thanks for the help.  Millermatic 135Syncrowave 250
Reply:I was at a very similar road around 9 months ago.  I have a large welder that is capable of drawing around 100 amps at 240 volts.  However, I believe I am wired for far less than that.  I think the breaker is a 50 amp breaker.  I've never tripped the breaker, many believe that theory that the welder will instantly trip the breaker if it is rated for such high amperage, and although the starting amperage can be a bit higher, in my opinion it isn't going to trip the breaker instantly.  This is from my own personal experience.  I think you will be fine.Miller 330 a/bp water cooledI believe in gun control, I hold my gun with two hands.  If you want to know why, click here.Buy American or bye America.
Reply:Hm.  I found a real good deal on a Miller Econotig so I may go look at that tonight.  I just really like the idea of having the service to my house be the limiting factor, not my machine.  Besides, the older machines seem to be built like tanks and the newer ones, well, not so much.Millermatic 135Syncrowave 250
Reply:My Shopmaster calls for 91A input at rated output (300A 50% duty). When I brought it home to do some welding in my garage I ran it off a 50A outlet with a 50' 6/3 extension cord. I had no problem running .035 wire on 3/8" sheet."Where's Stick man????????" - 7A749"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding"Stick-man"
Reply:Personally, when I'm installing a machine in the shop I always use the recommended breaker and wire size. It's more money in the beginning but you always have full capacity when you need it.On-site I don't have the same luxury. Sometimes all you can get is an undersized feed. In that case you have to limit your amperage and/or your duty cycle to not trip the breaker. A while back I was doing some trailer floors at a friends farm. Wired up my tig machine to his 50 amp breaker. Tripped it several times. In the end I had to turn down the heat a bit and take a few more breaks. This slowed the job but it was better than running into the shed and flipping the breaker every 15 minutes.