so i'm supposed to believe inverter ac somehow assumes a different waveform path?
i was under the impression the theory of true sine wave inversion synchronized
ergo, an amp is an amp is an amp, is it not?:?
be in in the 'panel', or 300' of UG urd....
~RJ~
It has nothing to do with waveform. And yes, the waveforms are (essentially) synced.
It has do with a) Kirchoff's law and the nature of parallel connections and b) thermal dynamics.
A panelboard busbar is a conductor with parallel connections all along it. Current can only flow in one direction at a time on a conductor. If you connect two synced sources at the far ends, there is no way the currents can add together per Kirchoff. Either one source will supply all the loads in between, or the two sources' current will combine somewhere in the middle on a load, not the main busbar.
However if you put the two sources near the same end, then their currents
can combine to flow towards the other end, if the loads draw that much, thus exceeding the rating of the bus.
By this logic, the 120% rule could be a 200% rule when the opposite end is adhered to. But UL and the CMP say: "wait a minute, all these breaker connections heat up at full current. And we don't test these panelboards for that." Say you have a 200A bus and the main breaker feeding a 200A load right next to the main, both of those connections heat up right next to each other. They test for that. They don't test for an inverter feeding another 200A load somewhere else on the same bus at the same time, which would be twice as much heat that the busbar has to dissipate. So they've given us this 20% allowance, for which we should be thankful I guess.