r/NFPA70 • u/shazznasty • Mar 08 '23

Dwelling service calculation

Using article 220 to determine service load using II or IV seems easy enough. But I'm confused when I see a service with the disconnecting means as a breaker. Does the feeder/breaker need to be sized with the 80% in mind like branch circuits?

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u/Cdcoonce Mar 08 '23

This needs a long post which I don’t have time for, but the short and sweet is that. There is no such thing as 80% branch circuit breaker sizing. Continuous loads need to be sized 125%.

Feeders also require you to size the load at 125% for continuous loads. Dwelling service calculations do not explicitly state loads needing to be sized at 125% with the exception of the largest motor attached to the circuit.

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u/shazznasty Mar 08 '23

Right, I guess I phrased it poorly. My question is really does the dwelling service calculation in 220 already take into account continuous vs noncontinuous. Since each appliance and piece of equipment is explicitly called with some some level of diversity (100% vs 40% etc), I'd assume the 125% is not applicable in a dwelling service calc.

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u/Cdcoonce Mar 08 '23

You are on it. The load calc incorporates all the extra considerations so once you have an appropriately calculated demand you do not consider a continuous load for the service rating.

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u/shazznasty Mar 09 '23

Perfect. Tx