Would it be code compliant to use the calculated service load as the basis for sizing a stand by generator to meet the requirements of 702.5 (B) (2) (a)? How do AHJ's actually determine if the generator is going to be overloaded? Is a test run made with everything connected operating at 100%? The reason I ask is that I have spoken with several contractors who tell me that as long as the unit starts and shuts down it's approved.. The answer I get when I ask about load shedding is" we just tell the customer to use common sense". I've also heard "when the breaker trips on the generator you are trying to run too much".Is this a grey area that is loosely enforced?
702.5 B(2)(a) 2008 reference
- Thread starter nizak
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Calculated load is a good place to start. Some AHJ actually require it with an ATS. If you shed loads, you just leave them out of the calculation. However, 702.5(B)(2) doesn't actually say the calculated load. It says, "The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment." So it'll depend on how the AHJ interprets that. Strict adherence to Code would mean using the calculated load.
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As a general rule, the generator cannot drive enough current into a non-short-circuit overload to trip its own breaker.
An unbalanced load on a single phase could trip the breaker though, since the prime mover can deliver enough power to one phase to do that.
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An unbalanced load on a single phase could trip the breaker though, since the prime mover can deliver enough power to one phase to do that.
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