Generator Interlock for 400 amp residential

[Sberry]

The fix to this is to put all of the generator loads in one panel.

As I mention I would do this differently if I was going to do it again, was 25 yrs ago and way before this forum. I have 14 panels connected to this over 4 buildings and a well.

 

[wwhitney]

2. Paralleling; the two neutral conductors of a single inlet supplying two panels will inadvertently be interconnecting the two neutral buses.

Given that such paralleling happens whenever you have multiple services and each service has its own GEC connection, is the paralleling from the inlet really a problem? Both in practice and code-wise (possibly different answers)?

Cheers, Wayne

 

[hillbilly1]

Given that such paralleling happens whenever you have multiple services and each service has its own GEC connection, is the paralleling from the inlet really a problem? Both in practice and code-wise (possibly different answers)?

Cheers, Wayne

I don’t think it’s a big problem electrically, unless the loads are really really unbalanced, but code wise, I don’t think the CMP really takes that into account because of so many variables, so they play it safe.

 

[kwired]

There are two separate neutral topics being discussed here: bonding and paralleling.

1. Bonding; a generator's neutral should not be bonded when supplying a load whose neutral is bonded, but it should be bonded otherwise.

2. Paralleling; the two neutral conductors of a single inlet supplying two panels will inadvertently be interconnecting the two neutral buses.

Sorry didn't read all threads yet so maybe this came up maybe not, but is that actually a problem? Particularly if both are service disconnecting means?

They are interconnected anyway even if you didn't try adding the standby system and when running from utility there will be shared current between both of the anyway. When running on generator current isn't flowing back to meter or utility it is flowing back to the generator.

Since they are service disconnecting means other rules will require them to be adjacent to one another so not quite the same thing as running a generator supply to two different feeder supplied panels located on opposite ends of the building where you could have current looping all the way back to the service and out through the other feeder circuit.

 

[kwired]

As I said above, the best solution is to use only one panel for desired generator loads, IMO.

or bite the bullet and go with a 400 amp transfer switch ahead of the two panels

 

[Frank DuVal]

Sorry didn't read all threads yet so maybe this came up maybe not, but is that actually a problem? Particularly if both are service disconnecting means?

I agree, show me what wire could possibly be overloaded if I feed one generator, with the neutral unbonded in the generator, to two panels, using 4 wires to each, that happen to have the neutrals connected together in the meter socket?

The generator (in this case given) has a capacity to provide 30 amps per leg (not per phase, that is a discussion for another time single phase you know!) and protects those two legs with 30 amp breakers. So the maximum unbalanced neutral current is 30 amps, even if a white becomes disconnected in a main breaker panel. 10 AWG wire. Why the discussion?

I too did the 2 200 amp panels because I could. Now after 20 years of joining circuits from one panel to another to get what the family needs to run, like last night when the power went out because of a fallen tree, and still not having light where needed, I'm ready to do the two interlocks instead of the 6 circuit Generac box from 20 years ago. And just manage loads as I do now, with my hands, but better.

 

[Frank DuVal]

or bite the bullet and go with a 400 amp transfer switch ahead of the two panels

Too hard to install without major wiring change through brick or concrete in my case. Of course, if someone was paying me to do it, easy! And it seems silly to buy a 400 amp transfer switch for a 30 amp supply.

 

[Joethemechanic]

I think the potential problem was that should one of the neutrals coming from the meter socket to the panels fail. the #10 neutral that is tieing the two panels neutral bars together would end up carrying one panel's neutral load. Mind you, this would have to happen while on POCO power.

Very slim chance of a problem, but it is possible

 

[kwired]

I think the potential problem was that should one of the neutrals coming from the meter socket to the panels fail. the #10 neutral that is tieing the two panels neutral bars together would end up carrying one panel's neutral load. Mind you, this would have to happen while on POCO power.

Very slim chance of a problem, but it is possible

Depending on how you did your grounding electrode(s) you might have another larger interconnection between the two panels. Good, bad, ugly, you potentially can have another interconnection via metallic service raceways also.

 

[Joethemechanic]

Depending on how you did your grounding electrode(s) you might have another larger interconnection between the two panels. Good, bad, ugly, you potentially can have another interconnection via metallic service raceways also.

My original thought was to only land the generator neutral in one panel and let the neutral in the service from the meter's neutral carry nutral current, but that has potential problems should someone decide to go into the meter socket and really isn't going to be compliant.

Two inlets seems to be the best idea so far

 

[Joethemechanic]

Size the neutrals going to the connection for the generator inlet for 200 amps, size your hots for 30, and use conduit??