Generator feeding 2 panels

[Steviechia2]

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?

 

[RUWired]

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?

I would think 250.24(A)5 would be a problem. You are regrounding the grounded neutral conductor down stream by means of the main bonding jumper in the other units main panel. That would put the neutral and equipment ground in parallel with each other.

 

[Gregg Harris]

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?

445.19 Generators Supplying Multiple Loads. A single generator supplying more than one load, or multiple generators operating in parallel, shall be permitted to supply either of the following:

1. A vertical switchboard with separate sections
2. Individual enclosures with overcurrent protection tapped from a single feeder for load separation and distribution if a generator(s) is provided with overcurrent protection meeting the requirements of 240.15(A).

 

[ceb58]

I would think 250.24(A)5 would be a problem. You are regrounding the grounded neutral conductor down stream by means of the main bonding jumper in the other units main panel. That would put the neutral and equipment ground in parallel with each other.

As long as the neutral and EGC were separated in the generator he would be OK.

 

[Steviechia2]

As long as the neutral and EGC were separated in the generator he would be OK.

Which I believe most generators they are.

The neutrals from each panel will be connected together in the remote gen plug

 

[hillbilly1]

As long as the neutral and EGC were separated in the generator he would be OK.

Wouldn't matter, if he is using a single plug to the generator, it's neutral would be common to both panels, hence a parallel path. If two plugs were used, the neutrals would be seperate, at least until they were plugged into the generator. Probably the only correct way would be two four pole manual transferswitches feeeding sub panels instead of the whole house. I know thats not the answer the OP wanted to hear, but with one generator, that would be the only legal way to do it. It's that or buy two generators, one for each unit.

 

[Smart $]

Wouldn't matter, if he is using a single plug to the generator, it's neutral would be common to both panels, hence a parallel path. ...

I'm not seeing why the parallel neutral path is a problem...???

 

[hillbilly1]

I'm not seeing why the parallel neutral path is a problem...???

There would be current flowing on this conductor because it effectively parallells the neutrals feeding the panels, let's say there's 30 amps unbalanced current in panel 1, panel 2 has a balanced load at 0 amps, since they are effectively paralled, the current would be divided between them, 15 amps would flow on panel 1's neutral, while panel 2, would have 15 amps also. the point that the neutral is jumpered together coming from the generator would also have 15 amps on it. If the receptacle is 30 amp, we would assume the wire size is#10, at this point, the wire will not over heat, but..... if the unbalanced current is increased, say 80 amps (not likely on a single phase 400 amp total size service though) then the current would be 40 amps on that #10 jumper. Then there's the code ramifications of paralleling two different feeders.........Remember, the neutral is considered as a hot wire once it leaves the service disconnect. Would you parallel hots from two different panels?

 

[RUWired]

As long as the neutral and EGC were separated in the generator he would be OK.

I see it a little different, Even though they are seperate at the generator, the main bonding jumper in each others panel ties them back together.

 

[ActionDave]

As long as the neutral and EGC were separated in the generator he would be OK.

I agree.

I'm not seeing why the parallel neutral path is a problem...???

I'm not either.

 

[ActionDave]

I see it a little different, Even though they are seperate at the generator, the main bonding jumper in each others panel ties them back together.

Eliminate panel number two and it looks like a non separately derived system. Add the second panel and you have an extra layer of detail, but still just a non-SDS.

 

[Smart $]

There would be current flowing on this conductor because it effectively parallells the neutrals feeding the panels, let's say there's 30 amps unbalanced current in panel 1, panel 2 has a balanced load at 0 amps, since they are effectively paralled, the current would be divided between them, 15 amps would flow on panel 1's neutral, while panel 2, would have 15 amps also. the point that the neutral is jumpered together coming from the generator would also have 15 amps on it. If the receptacle is 30 amp, we would assume the wire size is#10, at this point, the wire will not over heat, but..... if the unbalanced current is increased, say 80 amps (not likely on a single phase 400 amp total size service though) then the current would be 40 amps on that #10 jumper. Then there's the code ramifications of paralleling two different feeders.........Remember, the neutral is considered as a hot wire once it leaves the service disconnect. Would you parallel hots from two different panels?

I'm aware of all that. Is there is any violation? I don't see any... directly. However, I do have a safety concern regarding parallel neutral-current paths, but not exactly what you have described...

Say the generator is of a substantially lower rating than the service, where load shedding is on the consumer under standby power, and the wiring for the standby power source is sized according to generator capacity. Under utility power, the connection of standby neutral wires still presents a parallel path for utility neutral current...

Say the service is 400A, and the 2 panels are fed with 200A hots but 150A reduced-size neutral and the genset is wired in at 50A total and split at 50A to each panel, hots and neutrals. If the maximum unbalanced current is 150A for one panel, the parallel path may have to carry approximately one-half the maximum unbalanced neutral current (~75A) at some point in time...!!!

So where's the violation???

 

[hillbilly1]

I see it a little different, Even though they are seperate at the generator, the main bonding jumper in each others panel ties them back together.

View attachment 7626

I'm aware of all that. Is there is any violation? I don't see any... directly. However, I do have a safety concern regarding parallel neutral-current paths, but not exactly what you have described...

Say the generator is of a substantially lower rating than the service, where load shedding is on the consumer under standby power, and the wiring for the standby power source is sized according to generator capacity. Under utility power, the connection of standby neutral wires still presents a parallel path for utility neutral current...

Say the service is 400A, and the 2 panels are fed with 200A hots but 150A reduced-size neutral and the genset is wired in at 50A total and split at 50A to each panel, hots and neutrals. If the maximum unbalanced current is 150A for one panel, the parallel path may have to carry approximately one-half the maximum unbalanced neutral current (~75A) at some point in time...!!!

So where's the violation???

Good drawing illustrating this, but even if the neutral and ground is not bonded at the service for some reason, the neutrals are still paralled, part of the current would travel to the generator and back to the other service. This would still happen even with the bond disconnected at the generator. With the bond connected at the generator, it creates even another alternate path through the EGC. When I get a chance, i will have to look up any NEC violations, but it is a bad electrical design to do it this way. Try this with a Ground fault switch gear and let me know how it works out for you!

 

[RUWired]

Eliminate panel number two and it looks like a non separately derived system. Add the second panel and you have an extra layer of detail, but still just a non-SDS.

I don't think there was a question about it being a SDS.

The problem here is a safety concern (and a code violation, 250.24(A)5). If the neutral conductor should come loose or break in either unit while the generator is running, all the current in that unit would flow onto the EGC via the main bonding jumper in the other units panel. It could also flow onto the incoming neutral on the line side of the main, which could cause serious harm to personel working on the line.

 

[Smart $]

I don't think there was a question about it being a SDS.

But it is NOT an SDS when the generator neutral is solidly connected to the service system.

The problem here is a safety concern (and a code violation, 250.24(A)5). If the neutral conductor should come loose or break in either unit while the generator is running, all the current in that unit would flow onto the EGC via the main bonding jumper in the other units panel. It could also flow onto the incoming neutral on the line side of the main, which could cause serious harm to personel working on the line.

It's not a violation of 250.24(A)(5) if the generator neutral and egc are isolated. Fault current will always want to return on the generator neutral conductor(s). Yes there is a chance, under fault conditions where neutral current could get back through the service neutral, but the chances are minimal, perhaps only slightly higher than any conductor has of carrying fault current which did not originate on it.

 

[RUWired]

But it is NOT an SDS when the generator neutral is solidly connected to the service system.

Yeah, I did say that wrong.

It's not a violation of 250.24(A)(5) if the generator neutral and egc are isolated.

That would be correct, but the OP has the main bonding jumper in the opposing unit in the circuit. That bonding jumper is grounding the grounded conductor down stream of the service in unit # 1. and like wise for unit # 2. That is where the violation is.

 

[Smart $]

..

That would be correct, but the OP has the main bonding jumper in the opposing unit in the circuit. That bonding jumper is grounding the grounded conductor down stream of the service in unit # 1. and like wise for unit # 2. That is where the violation is.

The way I read the OP, he has two side-by-side service panels with MCB and MBJ in each. I see no violation.

 

[Smart $]

As long as the neutral and EGC were separated in the generator he would be OK.

Which I believe most generators they are.

...

I'm of the impression portable generators are typically furnished with the neutral bonded to receptacle EGC's and the generator frame (i.e. chassis ground). The neutral will have to be isolated when connected.

 

[hillbilly1]

I'm of the impression portable generators are typically furnished with the neutral bonded to receptacle EGC's and the generator frame (i.e. chassis ground). The neutral will have to be isolated when connected.

Some do, some do not. I have a 5500 watt that is not, the manufactures instructions show making a 15 amp plug with the ground and neutral jumpered together if bonding is required. My uncles Honda is bonded and has a gfci breaker on it, it will trip if you plug it into a manual transfer switch that does not break the neutral.

 

[RUWired]

The way I read the OP, he has two side-by-side service panels with MCB and MBJ in each. I see no violation.

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.