Generator Hook Up to 2 Metered Panels


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Old 03-01-21, 08:25 AM
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Generator Hook Up to 2 Metered Panels

Hello,

Newbie to this forum and first post. I am looking to find some answers to a generator hookup question. I would like to hook up a single portable generator to 2 metered panels (2 family house) with a 30amp feed. Both panels will have GenInterlocks kits installed to prevent backfeeding to the service lines and selective load on the both panels as not to overload the gen. Found similar post in this forum but it's a bit dated and it will not allow me to post replies/comments - Standby Generator Serving 2 Metered Panels. It sounds like it's exactly what I am looking to do but there's no conclusive comment. I am also thinking of the "Y" split from the gen feed to each panel BUT I am concerned how the Neutral and Ground on each panel would play into this setup, or if it's any issues at all. I imagine problem will arise similar to bonding the Neutral to Ground on a subpanel but I am just not certain and hoping someone knowledgeable in this forum can help answer my concern.

Comments and other suggestions on how to achieve the hookup is greatly appreciated.

Thanks in advance.

M
 
  #2  
Old 03-01-21, 09:53 AM
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Usual understanding of a standby generator is the transfer is by an automatic switch and a portable generator transfer is by a sequence of manual operations. Who will be the custodian of the 2 electrical panels described by you when utility power is lost and later comes back on to insure there is no backfeed and/or overload by either panel when using the portable generator?
 
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Old 03-01-21, 03:42 PM
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@beelzebob

All handling of the transfer will be by me.

Thanks
 
  #4  
Old 03-01-21, 04:33 PM
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Even with the generator feeding two panels with the equivalent of a Y connection, there will be no generator power infiltrating the utility power lines. And when one or both of the residences is switched to utility power using the interlocks, there will be no interconnection of hot lines with the other residence.

The Y split should be part of the generator hookup cords, not part of the wall wiring between the panels. This means that there would be two inlet boxes to connect the generator with. This way, if the generator hookup cords are removed when the generator is shut off then no neutral current will return to the urility lines via the other residence's panel. But even if some neutral current took the "wrong" path, nothing bad will happen.
 
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Old 03-02-21, 10:08 PM
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Hi AllanJ,

thanks for your reply. My generator has only 1 x 30amp plug that will support panel hookup. Not sure if I was clear when I said I was thinking of the Y option. Since there’s only one 30amp plug, i can only have 1 inlet box. The generator whip cable will plug into the receiver inlet box thru the garage and before terminating into one of the electrical panels, I would install a junction box that will allow a split to both panels with 10/3+ground wire. Now for my original concern, since they are independent feeds, would the utility Neutral cause any issues with the return path?

just in case if anyone ask why I would hook up 2 panels with such a small feed. Short answer is, I am aware of the limited capacity but any load put on the generator will be managed as not to exceed the max capacity.

Thanks again.

M
 
  #6  
Old 03-03-21, 06:01 AM
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You may construct a Y connector whip with two female ends and one male end. (But you should never construct, possess, or use a whip cord with more than one male end.) You will need a junction box to hold the wires converging into the Y since the plug behinds is not large enough.

There should be exactly one possible path (excluding dirt, earth, or soil) from a load (or a receptacle) back to the utility pole transformer. and also exactly one possible neutral path, accompanying that hot path..This will be true in a correctly wired system with the usual one and only one neutral to ground bond in the main panel.

With the Y connection, the preceding rule will be violated. Some of the neutral current resulting from something (light, appliance) plugged in and turned on may take either of two alternate neutral paths according to some equilibrium or balance that takes Ohm's law to understand. But no issues will be caused.

With the Y connection in the whip as opposed to in the wall, the choice of neutral paths won't be there when the generator and whip are removed.

Optionally you may use, say, 50 amp instead of 30 amp inlets and 6 gauge wire to the respective panels, anticipating upgrade to a larger generator. You may construct whip adapters with a larger (amperage) female end compared with the male end. But a smaller female end connected to a larger male end requires a box with a breaker matching the smaller end in between. Now it might be noted that generally a smaller generator (with appropriate manual discipline to avoid overloads) will consume less fuel compared with a larger generator for a given loading (within the capability of the smaller generator)..
 
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Old 03-03-21, 09:22 PM
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@AllanJ,

No Suicide Cable - GOT IT!!!!
Your comment about "exactly one possible neutral path" is the exact underlying reason for my post. I think your "Y connection in the whip" is essentially the same as what I was thinking of with my "Y" design in a junction box - I've included a quick & dirty drawing below for visual. I believe both designs will yield the same result where the neutral current will travel on both neutral lines with some current going back to the generator and some to the other panel. Would this be accurate? Your comment "But no issues will be caused" - would this apply to my last point about neutral current going to the generator and the other panel? Would the neutral in panel 1 have more current than a load draws (ie: a toaster) WHEN some load is put on the neutral from panel 2 and then trips the breaker? I hope my last question is clear.

Good advice on the 50amp but I've already invested in a 30amp install.

Thanks again


 
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Old 03-11-21, 05:29 PM
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Found this old link ... describes the hookup I wanted to do. Looks like a hazard that I was afraid of - possible parallel neutral paths.

https://forums.mikeholt.com/threads/...-panels.99174/

 
 

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