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Thread: Welding distribution panel

  1. #1
    Join Date
    Aug 2017
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    Buffalo
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    Welding distribution panel

    Hey man,

    Have a problem and need some advice.
    Working in a school, installing some new distribution panels. Panel #1 800amp feeds several other small panels. Panel #2 also fed from #1 and is also a 800amp panel but plans call for a 450amp breaker and parallel 4/0 between the panels.
    When I installed guts for panel #1 the breaker to feed panel #2 turned out to be a 800amp breaker so I ordered a 450amp breaker plug to replace the 800amp plug.
    Ok here is where things go south, panel #2 is to feed 12 welding booths and buy my calculations has max load of 540amps(of course you would never run all welders at same time). The engineer that designed this (who is also the inspection authority in this case) is saying that he does not want the 450amp breaker plug installed and buy NEC code you are allowed to de-rate panel feed wires buy 200%. I cannot find this code allowance and very concerned that this is a potential disaster. As far as I can find panel to panel feed wire sizes are simply calculated based on the size of breaker feeding them. All the rest of panel feeds in building are correct as are every panel I have ever installed.
    Are you aware of any code that would allow this engineer to get away with this?

  2. #2
    Join Date
    Jun 2003
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    I agree with you. There are some demand factors for welders that reduce the feeder size, but the breaker protecting the wire still has to be sized for the wire. Dual 4/0's would be 460 amps.

    There is a paragraph that lets you go up to the next size breaker if its under 800 amps, and the wire rating is not a standard breaker size. So you could also use a 500 amp plug.

  3. #3
    Join Date
    Nov 2007
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    812
    Quote Originally Posted by steve66 View Post
    I agree with you. There are some demand factors for welders that reduce the feeder size, but the breaker protecting the wire still has to be sized for the wire. Dual 4/0's would be 460 amps.
    630.12(B):
    "(B) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity."

    I guess the NEC specifies an OCPD range between 100 to 200 percent of the conductor rating.

  4. #4
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    Quote Originally Posted by topgone View Post
    630.12(B):
    "(B) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity."

    I guess the NEC specifies an OCPD range between 100 to 200 percent of the conductor rating.
    I stand corrected.

    I guess as long as there aren't any non-welder loads on the panel, it sounds code compliant.

    There is always the chance that someone could add some other loads to that panel in the future, but its still code compliant until then.

  5. #5
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    Aug 2017
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    There is a plasma cutter on the panel.

    Thanks for your help/advise guys. There is a plasma cutter on the panel along with the 12 welders wonder if that would count as a welder as well? I do not like it but if the code allows.

    Just do not think that 630.12(B):
    "(B) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity."

    Was written with a panel feed in mind. What if some wants to add equipment to that panel in the future. I would interpret it as a single panel breaker feeding 1 or more welder receptacles.

  6. #6
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    Aug 2017
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    Resolved

    Just found out that we are going to change the breaker plug to 500amp, take the plasma cutter out of the panel and label the panel for welding use only. So all good thanks for your input guys.

  7. #7
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    Nov 2017
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    Oregon City, OR
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    Agree!

    I agree. Special rules for welders just like motors....


    Quote Originally Posted by topgone View Post
    630.12(B):
    "(B) For Conductors. Conductors that supply one or more welders shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity."

    I guess the NEC specifies an OCPD range between 100 to 200 percent of the conductor rating.

  8. #8
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    Quote Originally Posted by B1vantage View Post
    Just found out that we are going to change the breaker plug to 500amp, take the plasma cutter out of the panel and label the panel for welding use only. So all good thanks for your input guys.
    Wonder if a plasma cutter qualifies as a welder? I know of combination welder/cutters....

  9. #9
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    Quote Originally Posted by Open Neutral View Post
    Wonder if a plasma cutter qualifies as a welder? I know of combination welder/cutters....
    They are made by the same companies, but more importantly have similar duty cycles (for component design and actual usage). I would argue that they should follow the same rules, but I wouldn't guess what an ignorant AHJ might say.

    One could easily label it as a welding machine circuit, and just plug a plasma cutter into it instead. No one would care, even if they noticed, and it would be perfectly safe, whereas plugging a heater into a welding machine circuit would be an obvious no-no.

    Back when plasma cutters first came out, that's what we did anyway, by necessity.

    Yeah, yeah, I probably shouldn't even be mentioning it. It's not a justification, just circumstantial evidence backing up the sound theory.

  10. #10
    Join Date
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    Quote Originally Posted by Open Neutral View Post
    Wonder if a plasma cutter qualifies as a welder? I know of combination welder/cutters....
    The two are different in that the plasma cutting uses a high velocity gas to blast away the molten metal it intends to cut while the gas being used in the plasma welding (TIG) is used to prevent oxidation of the welded metal. Same process of making the plasma but different velocities of the gases, IMO.

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