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  • Welder keeps tripping breaker.

    I use a fairly new millermatic 252 and recently it started tripping the breaker when ran on its higher setting. The breaker says 30 amp. Ive never had a problem with this before until recently. Just wondering if its most likely a problem with the welder or with the breaker. Thanks.

  • #2
    This machine requires 50A service.

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    • #3
      30 amps is not enough for that welder on higher settings. Check your owner's manual for the correct wire size and breaker size. DO NOT just install a larger breaker.

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      • #4
        I was thinking the same thing once i started looking at the specs on the machine, figured i would get a second oppinion. Thanks guys.

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        • #5
          The 252 (and I assume other heavy 250's) are the highest draw units with cord and plug supplied machines. They have a hi max output and high duty cycles and is the reason that the ready made welder cords come number 8 wire.
          With 035 wire and C25 the unit pulls about what a buzz box does, it will do it for a longer time. If we limited it to 20% we could use a 12 wire and a 50 under some circumstances. But, normally a home 30A circuit is 10 wire with a 30. Depending,,, this could be legal to go to 50 provided it was a buzzer on it and not a 250 feeder which could potentially overload it if one went to 045 and different gas. Not normally found in small shop/home brew outfits.
          I don't know if a guy at home could burn a house down with a 10 on one if he tried, I doubt it and almost bet its never been done. I use a 10 cord on mine if its got to move and cant warm it.
          Legally this machine needs to be connected to an 8 wire.

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          • #6
            My neighbor who is a master electrician for decades, inside wireman and could have anything he wanted still has the 50A outlet stapled to a stud with a 10 cable.

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            • #7
              I thought NEC said no more than 30 Amps on a #10 (from breaker to an outlet). None of the welder duty cycle exceptions or whatnot. Anything running to an outlet could have a full-current, long running device plugged in, like an electric space heater or motor.

              Run-of-the-mill 8 gauge NM-B should be good for 40A.
              Miller stuff:
              Dialarc 250 (1974)
              Syncrowave 250 (1992)
              Spot welder (Dayton badged)

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              • #8
                Actually, there is an exception to breaker size vs conductor size for welders. 2014 NEC Sect. 240.4.D, Small Conductors, has an exception in the lead-in para that takes you to Table 240.4.G, which in turn leads you to the Welder exceptions in Section 630. However, that gets a bit complicated to figure out. It is never good to starve a machine's input with too small of a wire. USMCPOP is right on-just use 8 AWG copper cable and a 50 A breaker per NEC section 310.18. If it is a very long run where cost becomes a big issue, go through the the calculations in section 630, and you may be able to save a couple of bucks, but power wiring is not the place to try to work "on the cheap". The NEC says right up front it is not a design document, but rather a safety document. Good design may go beyond safety minimums.

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                • #9
                  AC 224 or a Stickmate comes with a 12 cord plugged to 50A Probably the only model Hobart of Miller makes 50A that doesn't come with that cord is 230-250 They even use it on the 200 compact where they allow a 14/30 circuit to connect to it.
                  By using a cord 1 size bigger than the machine needs they can connect it to 50A circuits.
                  BTW and something I wanted to ask,, the MVP like my Max have 14, We assume there is something in the 50A adapter that allows this and I assume the new feeders that are dual V have a 14???
                  Last edited by Sberry; 05-24-2015, 11:02 AM.

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                  • #10
                    If you have a Maxstar 150, no issues at all with a 14 AWG cord on it from a legality viewpoint provided they choose the proper wire type (which I'm sure they did considering the flocks of lawyers that might be drawn to any problem attributed to Miller's design). The catalog lists the 150 at 26.4 A primary draw @ 115VAC, 35% duty cycle. That's the worst case since rated current draw is lower @ 230 volt input. So, 26.4Amps x .59 multiplier from NEC Table 630.11A (interpolated from the range of duty cycles -- table goes in steps of 10%) yields wiring ampacity rqmt of 15.6 amps. Table 310.15 allows for at least 20 amps in 14 AWG cable unless it is type UF or TW. Some 14AWG wiring insulation is rated for higher temp operation to 25 amps. (There is also a limitation on the breaker's temp spec but that's another set of considerations). So, by choosing the proper wire type to support 25 amps, and using the allowances for protection of both wiring and equipment for welders in Section 630, and Table 630.11A, you can get by with 14 AWG wire and a 50 A breaker. Would I wire the outlet for the welder this way? Not a chance. Just squeaking by minimum code reqmts is not a good idea! If I were doing it, for the difference in wire cost, I would use a minimum 10 AWG wire and a 40 A breaker, which would be far more conservative than code reqmts under the welder allowances. It is quite likely you could do with a 30A breaker--even better. Others may have different opinions--this is mine--I'm no expert just a guy who reads the Code. I can't imagine there is anything they could do in the MVP plug that would change any of this. Perhaps more info than you needed, but it was interesting to work through.

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                    • #11
                      A 14 wire cannot go on a 50A circuit. It needs to be 12,,, hence the 12 wire on the compact 230V wire feeders, they require 14 to operate but must limit the breaker to 30 as per the manual.
                      The 50A MVP plug must have a device3 in it,,, hence the warning about not modifying the cords, not that it wouldn't work but would throw it out of compliance.

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                      • #12
                        I believe the older Max where the user actually changed the end came with 12. Only when they came with the MVP plug did it drop to 14.

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