I'm working on a service upgrade where we're upgrading to two 200A services from a single 320A meter. As part of this install we're installing two service entry rated transfer switches between the meter and the panels to provide generator power during outages. The transfer switches are double pole units that break the hots only, the neutral connection is just a bus. Using the service entry rated switches I don't believe it's possible to directly connect both switches to the generator without a code violation on the neutral. I'm working with an electrician, but he doesn't have an answer to how this issue should be resolved. I also called Generac tech support who was also unable to advise. I'd like a verification from the experts here that my understanding is correct before I engage in expensive or unusual solutions.
Imagine the equipment laid out as so:
So the quick and obvious solution for the generator side is to split the feed in GJ, running two hots and a neutral from GJ to T1, and two hots and a neutral from GJ to T2. This will require the neutrals to be connected in GJ. However, this will cause what I'm calling a "ring neutral", which will then cause two current paths from T1 or T2 back to the meter or the generator. For example, when on utility power neutral current from T1 can flow to the meter direct via the T1-M connection, or follow the T1-GJ-T2-M connection. I believe this is a definite 300.20 violation, and likely other sections as well.
An alternate idea is to only connect the neutral to T1, running the hots through the GJ-T2 conduit still, and use the neutral through the meter to carry generator current when on generator. Utility power should be fine, and the T1 generator feed will be fine, but the T2 generator feed will not have grouped conductors which is also a 300.20 violation.
A third idea would be to not use the GJ-T2 conduit, only connect the generator neutral to T1, and have the T2 generator conductors parallel the utility conductors through the meter. As the T1-M and T2-M paths are service conductors this would be a 230.7 violation, even if the utility didn't balk.
Converting T2 to switch the neutral as well as the hots would resolve the issue. I called the distributor and there aren't service entry units that switch the neutral. The switches advertised as being able to be parelled in this fashion also don't break the neutral, so I think three must be another option.
I believe the root of my issue is that these are service entry rated switches. If the service disconnects were not in the transfer switches, but in a single enclosure with the ground bond, I believe it would be possible to route the feeds such that these issues go away. Is that what's being done on other multiple ATS installs? My electrician says it's possible to do a multi-ATS setup with service disconnects in the switches, but when I asked how the neutrals are routed he didn't have an answer.
Is there a solution I'm overlooking using these double pole service entry rated units in the grid configuration of my original drawing?
- Grounding is left out of scope of this discussion as the neutral alone has code compliance issues, before adding the complexity of bonding.
- Control wiring is out of scope.
Imagine the equipment laid out as so:
Code:
Panel 1 <-------- T1 ------- M --------< Utility
| |
| |
| |
Generator >------ GJ ------- T2 --------> Panel 2
M: Meter
T1 / T2: Service entry rated transfer switch
GJ: Generator junction box, to split the generator feed between T1 and T2- The service disconnects are in T1 and T2, as they are service entry units.
- There are two utility hots and a neutral between M and T1, as well as two utility hots and a neutral between M and T2. The neutrals are connected in M.
- There are two hots and a single neutral from the generator to GJ.
So the quick and obvious solution for the generator side is to split the feed in GJ, running two hots and a neutral from GJ to T1, and two hots and a neutral from GJ to T2. This will require the neutrals to be connected in GJ. However, this will cause what I'm calling a "ring neutral", which will then cause two current paths from T1 or T2 back to the meter or the generator. For example, when on utility power neutral current from T1 can flow to the meter direct via the T1-M connection, or follow the T1-GJ-T2-M connection. I believe this is a definite 300.20 violation, and likely other sections as well.
An alternate idea is to only connect the neutral to T1, running the hots through the GJ-T2 conduit still, and use the neutral through the meter to carry generator current when on generator. Utility power should be fine, and the T1 generator feed will be fine, but the T2 generator feed will not have grouped conductors which is also a 300.20 violation.
A third idea would be to not use the GJ-T2 conduit, only connect the generator neutral to T1, and have the T2 generator conductors parallel the utility conductors through the meter. As the T1-M and T2-M paths are service conductors this would be a 230.7 violation, even if the utility didn't balk.
Converting T2 to switch the neutral as well as the hots would resolve the issue. I called the distributor and there aren't service entry units that switch the neutral. The switches advertised as being able to be parelled in this fashion also don't break the neutral, so I think three must be another option.
I believe the root of my issue is that these are service entry rated switches. If the service disconnects were not in the transfer switches, but in a single enclosure with the ground bond, I believe it would be possible to route the feeds such that these issues go away. Is that what's being done on other multiple ATS installs? My electrician says it's possible to do a multi-ATS setup with service disconnects in the switches, but when I asked how the neutrals are routed he didn't have an answer.
Is there a solution I'm overlooking using these double pole service entry rated units in the grid configuration of my original drawing?