Generator feeding 2 panels

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suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Sure that could happen, but it seems to be an extreme example. You have both panels at maximum imbalance, and a generator sized to power the full rating of both panels. If the wires from the generator to each panel were sized to support the full load of the generator, then this will not be an issue. That would be the common implementation if you have a generator smaller than the sum of the service panels. If you have a 100A generator feeding two 100A panels -- you hope the total load will not exceed 100A, use 100A wire to each panel, and either panel could draw the max load, or 50A each.

I was thinking the OP was going to have a small generator, and not a 200A one.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Consider the consequence of the two units sharing the one generator should a neutral conductor come loose or break while in operation. The unit #1 owner will not notice any problems till the unit #2 owners wires burn up from overload. There is definitely a potential for problems that could be eliminated by keeping the two units neutral conductors isolated.

View attachment 7632
The current on the neutral would not be 200 amps because they are parrallel, with the 100 amp load, the maximum neutral current would be 100 amps if both 100 amp loads were on the same phase or leg.
 

RUWired

Senior Member
Location
Pa.
I was thinking the OP was going to have a small generator, and not a 200A one.
The OP didn't mention sizes. I put numbers in there for simplicity to show that with an open neutral in the unit #1 feeder,all the neutral current would shift to the unit # 2 neutral conductor and the EGC. The current could possibly be high enough to cause damage. This current can go undectected because of the down steam grounding of the grounded neutral conductor.Take away the down stream grounding and the open neutral stays within the unit#1 feeder and can be dectected.
 

RUWired

Senior Member
Location
Pa.
The current on the neutral would not be 200 amps because they are parrallel, with the 100 amp load, the maximum neutral current would be 100 amps if both 100 amp loads were on the same phase or leg.
Did you see the open neutral in the unit #1 feeder.
 

Smart $

Esteemed Member
Location
Ohio
The current on the neutral would not be 200 amps because they are parrallel, with the 100 amp load, the maximum neutral current would be 100 amps if both 100 amp loads were on the same phase or leg.
Did you see the open neutral in the unit #1 feeder.
Neutral current still has a parallel path, 1) through the generator-circuit EGC and 2) through the services' neutral.

And as Mark pointed out, you are showing a 200A load. Supposing the generator can deliver 200A, the wiring from generator to each panel would be rated for the full 200A. I don't believe the OP was proposing taps.
 

Steviechia2

Senior Member
Location
Massachusetts
And as Mark pointed out, you are showing a 200A load. Supposing the generator can deliver 200A, the wiring from generator to each panel would be rated for the full 200A. I don't believe the OP was proposing taps.
Only a 7000watt generator with an interlocking kit in both panels, 2-10/3 romex feeders to an outdoor 30 amp 125/250 volt male receptacle
 

Smart $

Esteemed Member
Location
Ohio
Only a 7000watt generator with an interlocking kit in both panels, 2-10/3 romex feeders to an outdoor 30 amp 125/250 volt male receptacle
The receptacle rated for landing 2 sets of #10?

You could run a single 10/3 then jumper from panel to panel if breaker terminals are rated for 2 conductors. If not, just splice off the feeder in the first panel. Given the prarallel neutral paths discussed, it's a better design.
 

Smart $

Esteemed Member
Location
Ohio
...
You could run a single 10/3 then jumper from panel to panel if breaker terminals are rated for 2 conductors. If not, just splice off the feeder in the first panel. Given the prarallel neutral paths discussed, it's a better design.
You could even run an oversized neutral for the jumper between panels, to reduce the possibility of the double fault hazard discussed.
 
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RUWired

Senior Member
Location
Pa.
You could even run an oversized neutral for the jumper between panels, to reduce the possibility of the double fault hazard discussed.
I still see a "grounded conductor" re-grounded down stream of the service disconnect, and a parallel neutral and ground conductor by joining the two panels together. Both of which are nec violations. I can also see Hillbilly1 concern of having the # 10 awg neutral between the two panels carrying any inbalance current. When Pulling the generator feeders neutral conductor off or landing it, i can see saturation current flowing across the worker. What do you think?

Common generator with two services (2).jpg
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
The Service Disconnect is both panel 1 and 2 (a grouped Service Disconnect), so it isn't being regounded outside the service disconnect. There is already a full size neutral betwee the two panels. Adding another one can't be avoided since you have one power source that needs to feed two panels and all related conductors need to be run together. These aren't parallel conductors each neutral isn't starting and finishing in the same lug body.

I think what arguments you're making could be applied to the two sets of conductors powering these panels from the utility (there are dual neutrals, there is N-G bonding in each panel, etc). The dual panel setup like this is very common in residential 400A services.
 
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RUWired

Senior Member
Location
Pa.
The Service Disconnect is both panel 1 and 2 (a grouped Service Disconnect), so it isn't being regounded outside the service disconnect.
I would say its is being regounded down steam of the 1st service disconnect even if they are side by side. I don't see where you could apply 250.142(A) to multiple disconnects.
There is already a full size neutral between the two panels. Adding another one can't be avoided since you have one power source that needs to feed two panels and all related conductors need to be run together.
I think by adding additional equipment to keep the neutral seperate is very possible.
The dual panel setup like this is very common in residential 400A services.
I agree and keeping the generator feeder neutral and ground seperate throughout the "system" is very important in both single or multiple dwellings. In the attached sketch, i quoted the article 250.142 handbook note applying to the OP's arrangment and why it should not be wired as such.

Common generator with two dwellings with open neutral.jpg
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
See the definition of what makes up a Service Disconnect in 230.71: The service disconnecting means for each service permitted by 230.2, or for each set of service entrance conductors permitted by 230.40, Exception Nos. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be not more than six sets of disconnects per service grouped in any one location.

So panel 1 and 2 are both the "service disconnect". N-G bonds can, and generally do, occur in both. This is due to the fact that the NEC can't force the power company to bring separate neutral and grounding conductors to your Service. The grouping of the Service Equipment and the fact there there are generally multiple grounded connections between the enclosures (conduits, GEC tails) helps to minimize the risks.

250.142(a) applies to the "Service Disconnect" which in this case is a group of enclosures.

Certainly, you could implement this with a single disconnect enclosure and isolate everything down stream, or put a jumbo neutral bar in one disconnect and isolate the neutral in the others while including a separate EGC. But the code doesn't require that, and it is usually cheaper to have multiple lower amp disconnects than to have one large one.

I don't see the hazards described as being "very important" to mitigate. 3 wire feeders to outbuildings were allowed for decades with few problems. A spark from a loose grounding connection isn't generally hazardous unless in a Classified environment (although you could argue that if natural gas appliances are present that is a hazard). If the neutral has totally come loose, you get some obvious warning signs for that. And many of these "hazards" still exist at all building services because fo what the utility provides.
 
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Raz5

Member
Location
OVIEDO
Occupation
Cost Manager
I have a 2 family with 2 main breaker panels next to each other. I want to put in 2 interlock kits 1 for each panel which will be fed by one remote plug to the generator.

I don't know of any violations here. What do you think?
Did you do this and did it work? I have 2 panels on my home and want to get power to both of them from 1 generator and an interlock in each panel.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
This is a situation that can only be properly accommodated by using a transfer switch (actually two transfer switches) that also transfers the neutral. Unfortunately that cannot be done with an interlock kit.
The breaker interlock method of transferring to a generator or other secondary power source is simple and inexpensive, but cannot be used in all situations.
 

Raz5

Member
Location
OVIEDO
Occupation
Cost Manager
This is a situation that can only be properly accommodated by using a transfer switch (actually two transfer switches) that also transfers the neutral. Unfortunately that cannot be done with an interlock kit.
The breaker interlock method of transferring to a generator or other secondary power source is simple and inexpensive, but cannot be used in all situations.
Thanks
 

Raz5

Member
Location
OVIEDO
Occupation
Cost Manager
This is a situation that can only be properly accommodated by using a transfer switch (actually two transfer switches) that also transfers the neutral. Unfortunately that cannot be done with an interlock kit.
The breaker interlock method of transferring to a generator or other secondary power source is simple and inexpensive, but cannot be used in all situations.
What about using GenerLink? Would it work and how is their quality?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
What about using GenerLink? Would it work and how is their quality?
I could not find any information on the GenerLink website to indicate either how it works or whether it has the needed extra pole to transfer the neutral connection. So no answer from me to your question on whether it would work.

Edit: On further examination, the fact that it can be mounted to a 4 jaw meter socket indicates to me that it cannot possibly transfer the neutral. Potentially good and NEC compliant for a single panel installation. But for the two panel configuration, the lack of the ability to isolate the two neutrals, both during normal power and generator power situations, makes it unusable.
 
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