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Is a 200 amp Panel only allowed 200 amps of loading

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  • #16
    Originally posted by rjniles View Post
    if the sum of each side sees more than the breaker rating it will trip.
    If a breaker exceeds its rating it will trip, but
    It's not determined by the sum of each side.

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    • #17

      yall are kinda scary here. first, don't post stuff you "think" might be correct. someone may end up relying on what you posted. electricity is dangerous and people die when they don't know what they are doing.


      now a typical residential panel in the USA has 2 hot legs coming to it, each are 120V. small homes and apartments are often set up for 100A or less on each leg. you can see what it is rated for by look at the meter or the main breaker in the panel (assuming it was installed and wired correctly). if it says 100A on the main breaker, that means 100A max for either of the two legs. Each leg can do 100A @ 120V.

      a typical outlet has 1 hot, 1 neutral, and 1 ground wire going to it... so that is 3 wires... and 1 of them are hot. this can power 120V devices.

      more power-hungry devices may need 240V (sometimes written 220V). this is 2 hot legs needed... 120+120 = 240. ... the 220 comes from 110V + 110V = 220V... this is roughly the lowest voltage considered normal for the motor/device in question. lower voltage and the device may not run. Some 240V applications only need 2 hot legs and the ground so it is still 3 wires, but has 2 hot legs instead of 1.

      now the breaker sizes in the panel only serve to tell you the max ampacity that the breaker will allow. that is ALL it tells you. don't assume anything else from that number. the COMBINED max load the panel can provide is as per the main circuit breaker. the only way to tell how loaded the panel is, is to find out how much load each circuit is supplying. this is normally done with a clamp-on meter of some sort, you add them up for all circuits, and that's your load. you might also be able to get a total number from your meter.

      a 2 phase (2-pole) breaker may have one or two switches on it. some are basically two single pole breakers linked together. if either of them trip, they both trip.

      the molded case circuit breakers while, for example, they may say 100A, will trip at 80% of that number if under a continuous load. it is based on heat generated. so a short duration instantaneous load won't trip at 80%, but a continuous load would. continuous means 3 or more hours non-stop.

      you can get FULLY RATED breakers that will trip, even at continuous load, at the number on the switch, but you know what you are getting when you do that. most residential house panels do not have FULLY rated breakers.

      now a 100A breaker supplying 240V power, is comprised of two 120V hot legs, each supplying 100A. so to calculate here, that is 100A x 120V = 12000 W EACH. For EACH leg added up, the breaker can supply a combined total of 2 x 100A x 120V = 24,000W of power, which is 240V x 100A. 2 x 120V = 240V. This is all single phase math.

      if you had a 3 phase service, this would be different. for example, a 100A breaker supplying 3 phase power = 3 hot legs of 120V. the math shorthand is 360x100A = 36000W @ 208V. ... 120V x 3 x 100A = 36,000W. .... 208V x sqrt(3) = 360.....






      Last edited by jdcpe17; 09-10-2021, 01:01 PM.

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      • #18
        Originally posted by jdcpe17 View Post

        the molded case circuit breakers while, for example, they may say 100A, will trip at 80% of that number if under a continuous load. it is based on heat generated. so a short duration instantaneous load won't trip at 80%, but a continuous load would. continuous means 3 or more hours non-stop.

        A circuit breaker will carry 100% of its rating forever. Even if it is subject to a small overload, say 5-10% it will carry the load for a while before it trips. You can load a breaker or a panel to 100% of it rating.

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