Circuit neutrals for a gen panel

[ToddB]

A friend is installing an 8-circuit standby generator/panel/auto bus transfer set-up. He asked a question of a couple of us that are electricians and there is a disagreement.

The set-up is pre-wired from generator to bus transfer/distribution panel, with just wiring required at his original service panel. The wiring for connection at the service panel has two feeders, a panel neutral, and a panel ground, as well at the eight individual circuit wires and eight individual circuit neutrals. Of course, the original hot wires for the circuits to be moved over to the generator panel are to be disconnected from the service panel and spliced to the corresponding circuit wires of the generator panel. He says the instructions do not address the neutral wires for the eight individual circuits. I say disconnect the eight circuit neutrals and connect them to the generator panel circuit neutrals, but another guy disagrees. Is there any circumstance where you would not want to re-route the individual circuit neutrals over to the new generator panel?

Thanks.

 

[chris kennedy]

If I am reading this correctly, I would suggest your co-worker review 300.3(B).

Welcome to the Forum.

 

[mcclary's electrical]

A friend is installing an 8-circuit standby generator/panel/auto bus transfer set-up. He asked a question of a couple of us that are electricians and there is a disagreement.

The set-up is pre-wired from generator to bus transfer/distribution panel, with just wiring required at his original service panel. The wiring for connection at the service panel has two feeders, a panel neutral, and a panel ground, as well at the eight individual circuit wires and eight individual circuit neutrals. Of course, the original hot wires for the circuits to be moved over to the generator panel are to be disconnected from the service panel and spliced to the corresponding circuit wires of the generator panel. He says the instructions do not address the neutral wires for the eight individual circuits. I say disconnect the eight circuit neutrals and connect them to the generator panel circuit neutrals, but another guy disagrees. Is there any circumstance where you would not want to re-route the individual circuit neutrals over to the new generator panel?

Thanks.

If the tranfer switch breakes the neutral (I doubt it does) you must land take the neutrals off the service bus and connect to the eight neutrals coming fron the factory wiring. If the switch does not break the neutral (that's where my money is),,,,then it won't matter, just land em

 

[icefalkon]

Hmmm...are you asking if the neutrals go to the generator or to the house panels, or to the transfer switch setup?

 

[LarryFine]

Is there any circumstance where you would not want to re-route the individual circuit neutrals over to the new generator panel?

I say you don't need to. The circuits still orginate in the original panel.

"What about when they're on the generator?"

What then? Move them from panel to panel with every power outage?

 

[ToddB]

Thanks guys.

I was asking if the circuit neutrals needed to be moved to the new generator panel. I believe they do and I believe that Chris Kennedy's response explains why.

Thanks again.

Todd.

 

[TT009]

Is the generator panel connected to the service panel? According to 300.3 I would say either way the neutrals have to be terminated in the same panel the ungrounded conductors are terminated

 

[electricmanscott]

I never relocate the grounded conductors in this type of setup. Never even thought about it really.

 

[ToddB]

The circuit is pretty much as shown on Scott's post above, with the exception that the generator panel was supplied with 8 individual circuit neutrals along with the 8 individual circuit hots.

I agree that the 8 individual circuits will function correctly either way, but I see the reasoning for moving the neutrals to the gen panel along with the hots.

Thanks for all of your opinions.

 

[mark32]

I maybe installing a MTS for a friend next week and I was planning on wiring it just like the graphic in Scott's post. Does everyone agree it's code compliant?

 

[stew]

the neutral supplied with the generator panel is large enough to serve as the neutral for all the 8 circuits. The manufacturers instructions on these dont say anything about running separate individual neutrals back to the utility side. I have Installed many of these just like the diagram indicates.

 

[mark32]

I just got back from looking at the job and I may not be able to mount the TS where I had anticipated. The house has two panels, one at each end of the house. The sub panel houses all of the circuits, except one, the HO wants on the generator. This panel is in a finished part of the basement and the HO would prefer the TS be mounted in the garage next to the main panel, about 75' away. Sooo, could I feed the TS from the nearby main panel, run a few lines (Romex at one point and piped in thhn at another) to the sub panel (Using all the conductors as ungrounded conductors) splice onto the respective ungrounded conductors in the sub panel and in turn the circuits would use the neutral in the sub panel. What do you think?

 

[Volta]

I say you don't need to. The circuits still orginate in the original panel.

But if

... The wiring for connection at the service panel has two feeders, a panel neutral, and a panel ground, as well at the eight individual circuit wires and eight individual circuit neutrals. . .

Then don't the circuits actually originate in the transfer panel? I will admit that I don't quickly find any Section clearly prohibiting it, though. If the 60 amp neutral is in the same raceway, I would not expect heating from hysteresis, but we may see ten current carrying conductors when using utility power.

. . . I say disconnect the eight circuit neutrals and connect them to the generator panel circuit neutrals . . .

I agree.

I maybe installing a MTS for a friend next week and I was planning on wiring it just like the graphic in Scott's post. Does everyone agree it's code compliant?

Not really.

I just got back from looking at the job and I may not be able to mount the TS where I had anticipated. The house has two panels, one at each end of the house. The sub panel houses all of the circuits, except one, the HO wants on the generator. This panel is in a finished part of the basement and the HO would prefer the TS be mounted in the garage next to the main panel, about 75' away. Sooo, could I feed the TS from the nearby main panel, run a few lines (Romex at one point and piped in thhn at another) to the sub panel (Using all the conductors as ungrounded conductors) splice onto the respective ungrounded conductors in the sub panel and in turn the circuits would use the neutral in the sub panel. What do you think?

Like the OP's senario, the branch circuits must comply with Article 210. If the neutrals are not moved to the standby panel, then we have a very odd circuit. Part feeder neutral, part ungrounded conductors. Not a multi-wire circuit, though. As Chris pointed out, 300.3(B) will be hard to avoid with this plan. Especially in the THHN part.

 

[LarryFine]

Then don't the circuits actually originate in the transfer panel?

When the genny-panel loads are on utility power, each circuit originates at its original breaker in the regular panel, passes through a double-throw switch in the genny panel, and back to the original branch-circuit conductor.

 

[LarryFine]

I say disconnect the eight circuit neutrals and connect them to the generator panel circuit neutrals, but another guy disagrees. Is there any circumstance where you would not want to re-route the individual circuit neutrals over to the new generator panel?

I don't recall seeing a neutral bus in that type of genny panel. The whip only includes ungrounded BC conductors (two per circuit) along with the single neutral and EGC.

Those here who support the single uber-neutral should have no issue with these whips.

 

[LarryFine]

If the neutrals are not moved to the standby panel, then we have a very odd circuit. Part feeder neutral, part ungrounded conductors. Not a multi-wire circuit, though. As Chris pointed out, 300.3(B) will be hard to avoid with this plan.

Actually, as long as all of the conductors are in a single raceway, there will be no unopposed currents, just as with an added sub-panel: as long as the feeder and BC conductors use the same nipple, the currents will be equal.

Added: Now, if we were adding a genny sub-panel, rather than a pre-assembled genny panel*, it would be correct to relocate the neutrals, because those circuits will always originate in the new panel, whether on utility or genny power.


*By which I mean the kind with two conductors for each circuit in the whip and individual SPDT switches.

 

[James13]

Some Utilities do not "favor" solid neutral connection from a generator to thier service neutral because they are afraid of getting voltage sent back on their feeder because of your generator. That's the only reason i could think of...but i think either way works just fine

 

[Volta]

When the genny-panel loads are on utility power, each circuit originates at its original breaker in the regular panel, passes through a double-throw switch in the genny panel, and back to the original branch-circuit conductor.

But the OP's panel has provisions for two feeders, I imagine it to be dual interlocked 2p60a breakers, or similar. The 'original' branch-circuit breakers are no longer used. If so, the original panel is simply a junction point for the optional standby circuits, which originate in the transfer panel.

Otherwise, some transfer panels are designed for only a single feeder, from the generator, and each breaker is double throw, in which case the conductors in the whip are simply switch loops when on utility power, and a single neutral connecting the panels for generator power.

I don't like it, but still can't quite claim that it is in violation.

 

[Volta]

Actually, as long as all of the conductors are in a single raceway, there will be no unopposed currents, just as with an added sub-panel: as long as the feeder and BC conductors use the same nipple, the currents will be equal.

I agree. I was referring to Mark32's proposed plan with romex and piped in THHN, hard to picture exactly what was proposed . . .

Added: Now, if we were adding a genny sub-panel, rather than a pre-assembled genny panel*, it would be correct to relocate the neutrals, because those circuits will always originate in the new panel, whether on utility or genny power.

That is what I am imagining. The OP stated that there were eight neutral wires in the whip, and provisions for two feeders.

*By which I mean the kind with two conductors for each circuit in the whip and individual SPDT switches.

Similar undefinable circuit, turned around.

 

[mark32]

Thanks guys for the input. I admit what I proposed is strange in design and I don't believe I'd feel comfortable with the install if I went ahead and wired it in the fashioned I described. I'll probably just pull new circuits from the TS to the sub where I'll splice the ungrounded and grounded conductors in the usual and proper manner and, if allowable, just terminate the grounds on the sub's equipment ground bar. How about that?