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Is it possible to feed the house through a y adapter(one male, 2 female) out of 50 amp 240volt outlet or using two outlets from generator to feed two panels via interlocked circuit breaker. 50amp to one panel and 30 amp to the other panel. Both of them interlocked

320 class service(400 amp), 2 panels 200 amp each panel with 200amp disconnect enter image description here

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  • Can you post photos of your panels please? Also, I take it you have "400A" (Class 320) service to your house? Commented Oct 9, 2022 at 17:02
  • That generator is bonded neutral so you'd need to undo that if allowed by its documentation. I don't know if that's allowed. This much advice you'll get in any question on portable generators. But additionally ... if you do have ground/neutral bonding only in the panels, another problem would be that if one of the neutrals becomes disconnected between the gen and panels, the other one will take the combined load and could get fried if you have highly unbalanced 120V loads. That's a lot of ifs ... but it's possible.
    – jay613
    Commented Oct 9, 2022 at 17:09
  • You should edit additional info into the question, not post answers. You like this site because it's a clean and concise Q&A site that doesn't have the clutter and confusion of forums. If answers were used for additional info and chitchat, you wouldn't like it so much. Commented Oct 9, 2022 at 21:12
  • Can you post photos of the interior breaker panels that serve the branch circuits please? Commented Oct 9, 2022 at 22:56

2 Answers 2

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Absolutely not. It's a Code violation, because Code doesn't like having single points of failure where one ordinary and routine failure could burn your house down, or at least your generator (which would make a mess). And the failure in question is a common one we see all the time here. So no.

The issue is we can't have parallel/redundant paths for neutral. You must have only one path because if it fails we need the panel to fail. Otherwise neutral service current would siently take the alternate path, wildly overloading it.

And by the way, the problem isn't those inexpensive sliding-plate interlocks. We love those things and highly recommend them, as a rule.

But let's look at alternatives.

Consolidate all critical loads into 1 panel.

I gather this is a Class 320 aka 400A service, where they used two 200A main panels, and they're sitting right next to each other. If it's not I'll cover that next.

The savvy panel installer, whenever they put 2 service panels nearby, always runs at least 1 conduit between the panels, and preferably like 4. Why? Because you sometimes bring a circuit into panel 1 and then wish it was in panel 2. Under NEC rules, as long as the grounds are bonded, it's a simple matter of extending the hot and neutral wires through the conduit passage to the other panel. The circuit's safety ground can stay in the panel it was originally in, but the neutral MUST be extended to land in the same panel with the hots, Very Important.

For instance a friend had that setup. The right panel had only two 70A breakers for emergency heat (that the generator could never power anyway), and a 15A/120V breaker for the furnace air handler and thermostat. Moved that to the other panel and voilà, all critical loads are on one panel. Unfortunately sometimes builders "help you out" by scattering all your loads evenly across both panels. Well, that's what multiple conduits are for.

If the conduits are more than 2 feet long, you can have up to four 15/20A circuits in each conduit. If less than 2 feet long, look up the max number of wires allowed in that size conduit, you can have 150% of that many because of an exception. (e.g. if 14 wires allowed you get 21). Remember don't bring branch circuit grounds across. The best wire type to use for the extension wires is THHN, you must use white for neutral and non-white for hot. Tape the pairs (or triples) of wires together near each end so they are identified as the same circuit.

If the panels are right next to each other and even with each other, I would find two knockouts that are directly across from each other, get an "RMC conduit nipple" (aka short pipe) 1/2" to 1" longer than the gap, and 2 conduit nuts. That won't do for grounding, but it'll work as a pass-thru. If there is lumber in the way, consider powering down one panel and doing some "dental work" with a Dremel moto-tool to remove the offending wood.

Now that all your critical loads are in 1 panel, you know what to do!

Or, isolate with a transformer

Another way to create the essential neutral isolation, and still use the inexpensive interlocks, is to watch Craigslist for a domestically made, UL Listed 120/240V--240/480V isolating supply transformer. I occasionally see them pop up for $100-200.

You only need the transformer on one of the two panels. The goal is to disconnect neutral between them. So do it on the smaller panel.

Jumper the transformer primary (480V side) for 240V (parallel both windings) and that goes straight to the generator inlet.

Jumper the transformer secondary (120V side) for 120/240V. Neutral goes straight to the neutral bar. The two hot wires go to your generator interlock breaker, which is sized to protect the transformer from overheat. Take the "KVA" of the transformer (e.g. 5 KVA) and multiply by 4 to get amps (20 amps).

Transformers are sized 5, 7.5, 10, 15 KVA. If the transformer isn't sized like that, you're looking at the wrong kind of transformer. If they come in a black or red box with a goofy "everything socket" on the front, that's definitely the wrong kind, that's not even an isolating transformer and its' cheap junk off Amazon. Don't do that.

Or, a 3-pole "big knife switch" transfer switch on one panel

This is the other way I can offer. This will be wired to switch neutral (as well as the two hots) from utility to generator. Again, you only need this on one panel.

Unfortunately it must be sized for the largest current (i.e. 200A utility current) so it will be a very costly switch. Seems unlikely to be affordable, so I won't discuss it further.

Note that those hokey and costly 6/8/10 circuit "transfer switches" are of absolutely no use here. They do nothing to solve the problem at hand, they just waste money.

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    Can't consolidate into one panel, because outside panels feed the inside panels at two different locations. Interlocked generator breakers are outside and all of the loads are inside at sub panels.
    – Tom
    Commented Oct 9, 2022 at 19:46
  • @jay613 what OP says after your comment is exactly why I mentioned alternatives. Commented Oct 9, 2022 at 21:03
  • @Tom Clearly, whoever set it up that way was unaware of the neutral rule, or thought you would use 2 generators. Well if you can connect the two panels with a long enough conduit, the only trick is you can only have four 15-20A circuits per conduit if they're over 2' long, so, multiple condits. Remember you don't need to bring safety ground through. Otherwise pursue one of the alternatives I mentioned. Commented Oct 9, 2022 at 21:06
  • @Harper-ReinstateMonica actually my previous comment was just wrong and now deleted. But a Q on your two alternatives. Don't they require that the neutral/ground bond be switched also from the panels to the generator? IE you cannot wire the generator as floating, the bond HAS to be in the generator to solve the problem you highlight, and on utility the bond has to be reinstated to the panels. I might not understand all the details of your alternatives. But if the bond is always in the panels, won't the isolation of neutrals be negated by ground paths between the panels?
    – jay613
    Commented Oct 10, 2022 at 18:28
  • @jay613 no, I'm proposing a 3-pole switch or transformer for only one of the panels. The other one is still direct/2-wires-switched, and so that one still needs neutral-ground separation at the generator. The purpose of the switch/transfomer is to break a neutral loop where both panels' neutrals are connected via the generator wiring, which would be very destructive in case of a utility-side neutral wire break. Commented Oct 11, 2022 at 3:56
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This question is probably about the technique, safety, and compliance of connecting this to a house with two main panels. I'm not addressing the house side of this ... safety, compliance. Leaving that to those with more experience.

But in this answer, to address only the generator itself, my quick reading of the manual is that the generator is capable of being used this way. If you use a suitable 50A and 30A cord to connect those respective outlets to appropriate inlets, the generator's 50A and 30A breakers will correctly protect those cords and the generator will deliver up to 50A and 30A respectively.

It will deliver up to 62.5 amps total as long as the load is very well balanced on the two outlets and, if 120V loads, on the two sides of each outlet. This may be hard to implement in practice, but there are ways. For example, if you have one or two large 240V loads that mostly occupy the 50A side, and all your 120V loads spread more or less evenly on the 30A side ... you might come close to getting full capacity from the thing.

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