question about parallel generators
I have a 2300 generator that has a run speed of 1800 which is not enough to run my AC (30A). So my question is what is the smallest size generator I could use in parallel to bring it up to run the AC?...
Forum Discussion
Circuit breakers (well, the ones you're likely to encounter) are thermal or thermal-magnetic. On a generator I suspect often they're just thermal ones, as I think that's what the little push-button ones nearly always are. Household ones in panels are thermal-magnetic.
Anyway, both of these allow some overcurrent for short periods of time. For household breakers, there are standards that specify how quickly they must trip for various conditions, from basically instantaneously for a serious overcurrent (as in a short circuit, several times the rated current of the breaker) to holding indefinitely (at or below the current rating at standard ambient temperatures). This is a very good thing, as for instance starting a large motor in an appliance would otherwise cause the breaker to trip most every time; the instantaneous inrush current is very often greater than 20A.
A 30A receptacle is rated to conduct 30A more or less indefinitely, and you're allowed to load a 30A receptacle with a 30A load. The 80% derating applies to "continuous loads", which are loads that operate at their maximum current continuously for three hours or more. An RV is not a continuous load per the NEC, so the 80% derating does not apply here.
There are magnetic circuit breakers that react instantaneously to current over some approximately exact threshold, but they are used pretty much exclusively for specialized applications. One example is (some) theatrical lighting circuits. The difference between the breaker types is how they (traditionally, at least) are actuated: thermal breakers are tripped when a bimetallic link carrying the current heats up and bends, while magnetic ones trip when the current, which flows through an electromagnet of some sort, produces a strong enough magnetic field to activate the mechanism. Thermal-magnetic breakers have parts so the bimetallic strip also can trip through magnetic means if the current is very high.
Anyway, both of these allow some overcurrent for short periods of time. For household breakers, there are standards that specify how quickly they must trip for various conditions, from basically instantaneously for a serious overcurrent (as in a short circuit, several times the rated current of the breaker) to holding indefinitely (at or below the current rating at standard ambient temperatures). This is a very good thing, as for instance starting a large motor in an appliance would otherwise cause the breaker to trip most every time; the instantaneous inrush current is very often greater than 20A.
A 30A receptacle is rated to conduct 30A more or less indefinitely, and you're allowed to load a 30A receptacle with a 30A load. The 80% derating applies to "continuous loads", which are loads that operate at their maximum current continuously for three hours or more. An RV is not a continuous load per the NEC, so the 80% derating does not apply here.
There are magnetic circuit breakers that react instantaneously to current over some approximately exact threshold, but they are used pretty much exclusively for specialized applications. One example is (some) theatrical lighting circuits. The difference between the breaker types is how they (traditionally, at least) are actuated: thermal breakers are tripped when a bimetallic link carrying the current heats up and bends, while magnetic ones trip when the current, which flows through an electromagnet of some sort, produces a strong enough magnetic field to activate the mechanism. Thermal-magnetic breakers have parts so the bimetallic strip also can trip through magnetic means if the current is very high.
