OT- capacity of distribution panel
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    Default OT- capacity of distribution panel

    Good morning. This may be a stupid question but I am not an electrician and I have a question about an electrical panel. The panel I am dealing with is rated at 100 amp. It has a 100 amp "main" breaker. When I add up the breakers installed in the box, they equal way more then 100 amps. There are two sixty amp breakers (220v) and a handful of twenty amp breakers installed. Is this thing overloaded? The main never trips. Thanks.

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    No, it's not overloaded. If you try to pull more than a combined 100A, the main breaker will trip.

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    Quote Originally Posted by crossthread View Post
    Good morning. This may be a stupid question but I am not an electrician and I have a question about an electrical panel. The panel I am dealing with is rated at 100 amp. It has a 100 amp "main" breaker. When I add up the breakers installed in the box, they equal way more then 100 amps. There are two sixty amp breakers (220v) and a handful of twenty amp breakers installed. Is this thing overloaded? The main never trips. Thanks.
    If the main doesn't trip then it is not overloaded. Each breaker protects that branch of the circuit and the main protects the line feeding the panel. Almost all populated panels will have cumulative breaker capacity far exceeding the main breaker.

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    Without quoting code, the 100 amp main breaker is to protect the buss work in the box. The individual breakers protect the wiring connected to that breaker. The sum total of all the individual breakers could far exceed the capacity of the cabinet, but the sum total of all the individual currents cannot exceed the rating of the cabinet.

    Tom

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    So if you were using all the breakers at near capacity for some weird reason, it could overload the main correct?

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    Yes, see post 2.
    The code assumes you won't do this.

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    Thanks guys.

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    Most loads are not continuous they are intermitant. A 50 amp outlet for a stick welder is allowed to be run with 40 amp wire since half the time is spent switching to a new rod, chipping slag etc. The NEC figures plenty of time off to allow the wire to cool. If it is a mig welder you have to use the correct size wire.
    Bill D

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    There are a number of PRACTICAL assumptions that are built into the NEC. Not only does the code allow the total current of the individual breakers to exceed the to capacity/rating of the box and the drop from the power pole, but if you go around any house and count the 15 or 20 Amp outlets and the other loads, you will get a number that is even greater than that total for the individual breakers.

    The most firm rule here is that the breakers must be sized to prevent the wires from excessive current and therefore heat and the danger of fire. So you can not put a 20 or 30 Amp breaker on a circuit that has been wired with a gauge and type of wire that is only rated for 15 Amps. You can find many older houses that have only 40 or 50 Amp service but that have well over 100 Amps of devices in them. As long as the occupants of that house do not turn everything on at once, it works just fine with no fire or other safety problems. And no blown fuses or tripped breakers. This is perfectly OK according to the code and perfectly safe.

    The code is first and foremost about SAFETY. Safety from fire hazards and safety from shock hazards.

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    Quote Originally Posted by Bill D View Post
    Most loads are not continuous they are intermitant. A 50 amp outlet for a stick welder is allowed to be run with 40 amp wire since half the time is spent switching to a new rod, chipping slag etc. The NEC figures plenty of time off to allow the wire to cool. If it is a mig welder you have to use the correct size wire.
    Bill D
    How does the sparky wiring up a 50 amp outlet know what your going to plug into it ?...

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    Quote Originally Posted by digger doug View Post
    How does the sparky wiring up a 50 amp outlet know what your going to plug into it ?...
    Cuz you asked for a 50A receptacle there.

    It's a 50A outlet..... Yeah, you could connect a 200A load to it, but in so doing you are not using the parts "within their listing"..... which is both an assumption, and a requirement of the code.

    The code says that equipment must be :"listed for the use", and plainly, a 50A outlet is not "listed for" a 70, or 200A load.

    There is nothing foolproof. Fools are on a continuous improvement program for foolishness.

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    ["There are a number of PRACTICAL assumptions that are built into the NEC."

    Diversity Factor.

    Ie, you cannot all flush your toilets at the same time during superbowl halftime.

    If everyone on the block loaded their individual panelboards up to 85 percent load, the
    pole pig fuse would blow.

    If everyone in town got in their car and tried to drive to the store at the same time, giant
    traffic jam.

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    Quote Originally Posted by JST View Post
    Cuz you asked for a 50A receptacle there.

    It's a 50A outlet..... Yeah, you could connect a 200A load to it, but in so doing you are not using the parts "within their listing"..... which is both an assumption, and a requirement of the code.

    The code says that equipment must be :"listed for the use", and plainly, a 50A outlet is not "listed for" a 70, or 200A load.

    There is nothing foolproof. Fools are on a continuous improvement program for foolishness.
    Please read post #8 (which I quoted).
    Bill says only need to wire for a 40 amp load to a 50 amp outlet.

    I have been taught, that you wire for the ampacity of the outlet.

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    Quote Originally Posted by digger doug View Post
    Please read post #8 (which I quoted).
    Bill says only need to wire for a 40 amp load to a 50 amp outlet.

    I have been taught, that you wire for the ampacity of the outlet.
    I don't have a current copy of the NEC, but past versions that I've owned and/or looked at had a very specific provision for allowable ampacity for branches specifically (and only) intended for welding equipment, which do/did specifically treat them differently than other branch circuits.

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    Quote Originally Posted by kd1yt View Post
    I don't have a current copy of the NEC, but past versions that I've owned and/or looked at had a very specific provision for allowable ampacity for branches specifically (and only) intended for welding equipment, which do/did specifically treat them differently than other branch circuits.
    O.k.
    Would YOU wire a place like this, that's not your shop ?

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    If it is a 50 amp outlet I would use 50a wires to wire it. But if it was a 50 amp draw welding machine that was hard wired in I might use 40a wires (per NEC). No way for someone to unplug the welder to access the outlet.

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    Quote Originally Posted by Rob F. View Post
    If it is a 50 amp outlet I would use 50a wires to wire it. But if it was a 50 amp draw welding machine that was hard wired in I might use 40a wires (per NEC). No way for someone to unplug the welder to access the outlet.

    The welder allowance is SPECIFICALLY FOR hard-wired machines for that reason.

    ANY "receptacle" is by definition "general purpose", and if it is a 50A outlet, any schlemiel looking at it once it is put in is gonna say "oh, I can plug in up to a 50A load". And he'd be right, generally.

    BUT, the receptacle is good UP TO 50A.... It does not HAVE to have 50A capacity. It does not even have to have 240V etc on it, might be 36V 40A, as long as ONLY that voltage is used on that style of receptacle. A label is good..... of course .

    So, if the 50A plug has 40A wire going to it, that's PERFECTLY OK. BUT, you have to breaker that line at 40A if you use 40A wire.

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