Generic question here. I won't self-answer.

Suppose I am adding significant new loads to an existing house - say, a 50A hot tub and a 50A RV receptacle. Those are big loads for a modest gas home. It seems like I ought to re-compute the provision of power to make sure this is sane given my service.

I already know you don't just add up all the breakers on each leg! You are usually allowed (and should) have many more breaker amps than service amps, since they won't all run at once.

But then I think about big loads like hot tub , which will draw most of its 50A when it is on, which could be awhile if it is cold started.

How do I tally up all my circuits and special loads, and arrive at a number that my house should be provisioned with to support those loads?

  • Do you want a from-scratch recalc by the standard Art.220 procedure, or would you be open to using the 220.83 process for existing dwelling units? Also, are you envisioning covering the addition of HVAC loads, as that's a special case for 220.83 calculations? – ThreePhaseEel Jul 13 '19 at 19:31
  • I am not quite sure but would be concerned about trusting the original procedure. This is for a random asker, where there could have been several updates and no continuous process for tracking them all. So the house as we see it could be anything... – Harper - Reinstate Monica Jul 14 '19 at 1:36
  • yeah, neither process depends on having an existing load calculation, its just that the 220.83 process is somewhat simpler – ThreePhaseEel Jul 14 '19 at 1:58

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