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Am starting to put a generator setup together. I'm planning on setting up an interlock and backfeed breaker into my panel with an outdoor receptacle for the gen to plug into. The issue is this. My generator is older(its an old garden way with a cast kohler engine, 5500 and runs like a top), and is setup with a NEMA L6-20 for the 220 which I'm planning on using--it also has two standard nema 5 outlets. This means it is straight 220...so, can I just wire the whole thing 3 wire, no problem? meaning in the panel, the 2 hots to the backfeed breaker and the grd to the grd bus bar? Am I missing something, or do I need the neutral?
Thanks in advance for any input!enter image description hereenter image description hereenter image description here enter image description here

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    Well, with a NEMA 6 connection, your two hots will be 240V across, but with no neutral to stabilize them, your two 120V legs won't necessarily be 120V. They might be 130V and 110V... They might be 200V and 40V... Might be 230V and 10V. That could change minute by minute. Is that something you can live with? – Harper Dec 5 '18 at 6:33
  • Does your generator not have a NEMA 14 (four prong) receptacle whatsoever? – ThreePhaseEel Dec 5 '18 at 12:44
  • @Harper Thanks, interesting-sounds like that could be a problem and fry things plugged into the 110 outlets.... That appears to be how the main power seems to be coming into the house as well, a 3 wire setup, with a braided copper ground going from the ground bus bar to a well feed pipe. The house was built in 1960. Its an old Square d QO series panel with the main setup as a 2 pole 100 am breaker on the left leg, lowest spot. – woodsVT Dec 5 '18 at 13:35
  • @ThreePhaseEel nope, just theL6-20 and the nema 5's :./ – woodsVT Dec 5 '18 at 13:36
  • On your service entrance, that third bare wire is actually the neutral. Power companies don't supply ground as a rule. – Harper Dec 5 '18 at 16:26
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Running the house off the L6-20 receptacle (without the neutral) would be almost sure to start wrecking things on your 120V circuits in short order, blowing light bulbs, refrigerator, etc. And at the worst possible time, during some emergency.

Since there are 120V receps you know there's a 120V tap in there that can be used to supply line-to-neutral loads. However there's a chance it is too small to carry the full neutral load for this application. I am not sure, but from that wiring diagram but it looks like the neutral tab on the 120V receptacle is the neutral-ground bond.

I think it would be possible to modify the wiring and install a L14-30R receptacle, but it wouldn't be a modification I'd be comfortable making. The alternative would be to use a transformer between the generator and the backfed breaker, but at that point maybe you just buy a different generator better suited for the application .

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