I'll start off by saying that I am familiar enough with the electric code to know that either an interlock or manual transfer switch panel is required so as not to backfeed the electric lines.
I have a portable generator that I would like to connect to my home electrical panel. My generator, as with other generators I have seen, has 2 output plugs, one is a 4 prong twist lock 120/240v rated at 21 amps and the other is a 3 prong twist lock 120v rated at 20 amps. The total output from my generator is 5000 watts continuous or 41 amps total. The surge wattage is higher.
As I understand it I can not connect both output plugs from the generator to my electrical panel to get the full 41 amps due to load sharing not being equal (which could trip one of the generator breakers prematurely) and possible out of phase ac power from the different plugs on the generator.
So my first question is is that correct? It make sense to me.
Second, if I can not connect both gen outputs directly to my panel how do I get the full 5000 watts to my electric panel? I believe I understand the math here. If I only run 120v equipment, which is what I forsee, no need for 240v during a power outage, then 20 amps is 2,400 watts at 120v. So one of the generator plugs will not get the job done. I'll only have half of the gen output available.
Is my math and thinking above correct?
The only way I can see to get the full generator output into the house is by using both a backfeed breaker in my panel with the appropriate manual interlock per the electric code and also installing a manual switch panel.
I would run the generator output from the 120/240v 21 amp plug to a backfeed circuit breaker in my main panel (with appropriate interlock). After a power outage I can turn off all the main electric panel CB's, go off and on with the main and gen breakers via the interlock, power up the generator and have 21 amps (about 2500 watts) available to use as I see fit via the breakers on the main house electric panel.
Now, for the other output from the generator, the 120v 20 amp output I would connect to a 10 circuit manual transfer switch. I would only connect 120v loads to this panel because I would only have 120v coming into it. Now, flipping the rocker switches on the manual transfer switch panel from line to gen would disconnect the chosen circuit from the main panel power (wherever that power is coming from, the line or the other generator plug) and connect it to the second 120v generator output. This would make the other 20 amps (about 2400 watts) from the generator available to the manuel transfer switchs 10 circuits.
So after all is said an done I would have 120/240v with 21 amps from the generator available to all circuits of my main panel (yes I know I would not be able to run all circuits, I plan to install a watt meter so I can see how much power I am pulling on the main panel and I would not be powering the 10 circuits connected to the manual transfer switch once those switches are turned to gen). Second I would have the 120v 20 amp plug connected to a 10 circuit manuel transfer switch panel. During a power outage those 10 circuits would be disconnected from the main and connected to the generator.
Settings things up this way I would have 2 separate plugs from the generator powering two basically separate electrical systems which would in turn power the house. The parts for this setup including the cabling to the generator would be about $700 to $800.
Does anyone see a problem with this setup? Is there anything that would not be to NEC in doing this?
Am I over complicating this? Does anyone know of a better or more efficient way?
Any input on problems with this setup or better ways would be appreciated.