ECN Forum Forums Code Related Discussion NEC & other Code issues The sum of the ratings of the circuit breakers shall be permitted to exceed the ampac

The use of that exception is actually important to some installations. I have done a fair number of rural electrical installs for homes that have a well for their water supply. I always try to mount the service equipment off of the home as either a free standing service backboard or on a small expendable outbuilding. I avoid the use of a single breaker as the service disconnecting means for these installations so that a single fault in some other portion of the wiring is unlikely to deprive the well pump of power. This is usually more cost effective than using the exception to 230.72 that would allow a completely separate disconnect for the pump power. The exception to 230.72 only works when the well has a pump house or other out building quite close to it. In the absence of a separate building the power company usually wants a pole set to terminate the separate drop to. By building a free standing back board I avoid subjecting the customer to meter reading fees for a second meter and by installing an underground service I avoid the cost of setting a pole.
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Tom Horne

[This message has been edited by tdhorne (edited 06-07-2004).]

If you used an MLO panel with a back fed 100 ampere breaker, disconnect tie down, and a valid load calculation then it would be code compliant.

Once again if the load calculation is valid then where's the hazard?

I'm not unsympathetic to your concern. Perhaps the submission of language to require each disconnect to have no larger ampacity than the load it serves would require would partially address your concern.

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Tom Horne

[This message has been edited by tdhorne (edited 06-07-2004).]