Backfeed main panel from essential panel any code issues

[j s]

Beside my meter base I have two disconnects 1 is a 200 amp and feeds my main panel. The other is a 100 amp and feeds my essential loads panel. In these disconnects the neutral and ground are bonded together. The essential loads panel is backed up with a 20kw generator with a automatic transfer switch. My thought is to back feed my main panel out of the essential loads panel using a manual transfer interlock in the main panel that will require the main breaker to be turned off before the backfeed breaker can be turned on. This will allow me to select some loads in the main panel during extended outages. I would shut off everything in the main panel before before the transfer takes place and then turn on the desired load. My question is. Would there be any code issues with connecting the neutral and ground buses together between these two panels The back feed would leave the essential loads panel on a 10/3 romex using a 2pole 30 amp breaker and arrive in the main panel on the same.

 

[brantmacga]

In this scenario, the main panel would become a sub-panel of the essential loads panel, and you’d have an upstream neutral bond, which isn’t allowed.


There are a variety of ways you could probably reconfigure this service where the generator feeds both panels and use load shed devices.

Is it a 200A service or 320A service ?


Sent from my iPhone using Tapatalk

 

[jaggedben]

This is essentially the same as what as asked in this thread.

Interlock with 2 panels

Is there any known issues with supplying 2 panels from one portable generator using interlock kits in both panels? Would be a 30 amp breaker in both panels with interlock kits and both sets of conductors connected to a 30 amp inlet box. Read a brief article where someone said that shouldn't be...

forums.mikeholt.com

 

[j s]

In this scenario, the main panel would become a sub-panel of the essential loads panel, and you’d have an upstream neutral bond, which isn’t allowed.


There are a variety of ways you could probably reconfigure this service where the generator feeds both panels and use load shed devices.

Is it a 200A service or 320A service ?


Sent from my iPhone using Tapatalk

Thanks for the reply, its a 300 amp service. (200 amp main and 100 amp main) Not really interested in load shed devices there is plenty of generator to do what I want to do it would be rare that it would ever even be utilized. For example if I had a turkey in the oven on thanks giving and the power went out I would backfeed my main panel and finish cooking that thing.

Help me understand upstream bonded neutral. Both panels have separate neutral and ground buses. The neutral would not be connected to the ground in any way that I can think of.

 

[brantmacga]

This is essentially the same as what as asked in this thread.

Interlock with 2 panels

Is there any known issues with supplying 2 panels from one portable generator using interlock kits in both panels? Would be a 30 amp breaker in both panels with interlock kits and both sets of conductors connected to a 30 amp inlet box. Read a brief article where someone said that shouldn't be...

forums.mikeholt.com

I see this question as different in that OP wants to connect Panel A downstream of Panel B, not parallel.

 

[jaggedben]

I see this question as different in that OP wants to connect Panel A downstream of Panel B, not parallel.

But the issue of parallel neutral paths is essentially the same.

 

[jaggedben]

Help me understand upstream bonded neutral. Both panels have separate neutral and ground buses. The neutral would not be connected to the ground in any way that I can think of.

Your neutrals are still connected to ground in the upstream disconnects. But that isn't the problem. The problem is about neutral current.

Unless your ATS switches the neutral (not common) then when you run the circuit for the interlocked generator breaker you are creating a parallel path for neutral current. This is a violation of 300.20 and will cause slight heating on any metal conduit. It could also potentially overload the neutral on the interlocked circuit between the panels, particularly when running on grid power.

 

[brantmacga]

But the issue of parallel neutral paths is essentially the same.

My interpretation of the situation in this thread is that the neutral/ground bond is upstream of the essential loads panel, and that is the violation.

Maybe something isn't clicking with me, but I'm just not sure I can be in agreement on the parallel neutral issue described in the other topic, as it seems to be wholly dependent on having an installation defect for it to cause issues. I've never measured current on the backup neutral between two panels. I suppose one could install neutral-switching breakers as the back-fed main if its that concerning; the neutral would only be active while on gen power.

 

[jaggedben]

My interpretation of the situation in this thread is that the neutral/ground bond is upstream of the essential loads panel, and that is the violation.

It is in no way a violation to have a main bonding jumper upstream of an ATS. However you're correct, in a way, that the neutral/ground bond for the main panel ends up being load side when the generator is used as described.

Maybe something isn't clicking with me, but I'm just not sure I can be in agreement on the parallel neutral issue described in the other topic, as it seems to be wholly dependent on having an installation defect for it to cause issues.

Yeah, not sure what isn't clicking but there's definitely parallel neutral conductors in both situations unless one designs in some kind of neutral switching like you suggested. Draw it out.

 

[brantmacga]

Your neutrals are still connected to ground in the upstream disconnects. But that isn't the problem. The problem is about neutral current.

Unless your ATS switches the neutral (not common) then when you run the circuit for the interlocked generator breaker you are creating a parallel path for neutral current. This is a violation of 300.20 and will cause slight heating on any metal conduit. It could also potentially overload the neutral on the interlocked circuit between the panels, particularly when running on grid power.

Help me understand the issue you are seeing from 300.20.


300.20 Induced Currents in Ferrous Metal Enclosures or
Ferrous Metal Raceways.
(A) Conductors Grouped Together. Where conductors carrying
alternating current are installed in ferrous metal enclosures
or ferrous metal raceways, they shall be arranged so as to avoid
heating the surrounding ferrous metal by induction. To accomplish
this, all phase conductors and, where used, the grounded
conductor and all equipment grounding conductors shall be
grouped together.

Exception No. 1: Equipment grounding conductors for certain existing
installations shall be permitted to be installed separate from their associated
circuit conductors where run in accordance with the prouisions of
250.lJ0(C).

Exception No. 2: A singk conductor shall be permitted to be installed in
a ferromagnetic encwsure and used for skin-effect heating in accordance
with the prouisions of 426.42 and 427.47.

(B) Individual Conductors. Where a single conductor carrying
alternating current passes through metal with magnetic properties,
the inductive effect shall be mi.nimized by (1) cutting slots
in the metal between the individual holes through which the
individual conductors pass or (2) passing all the conductors in
the circuit through an insulating

Exception: In the case of circuits supplying vacuum or ekctric-discharge
lighting systems or signs or X-ray apparatus, the currents carried by the
conductors are so small that the inductive heating effect can be ignored
where these conductors are placed in metal enclosures or pass through
metal.

Informational Note: Because aluminum is not a magnetic metal,
there will be no heating due to hysteresis; however, induced
currents will be present. They will not be of sufficient magnitude
to require grouping of conductors or special treatment in passing
conductors through aluminum wall sections.

 

[brantmacga]

It is in no way a violation to have a main bonding jumper upstream of an ATS.

In OP's installation, the bonding jumper is installed at the ATS, and the essential loads panel is a sub-panel from that ATS, and his other panel would then be a further sub-panel from that. I'm going to assume this is a standard residential ATS, and not neutral-switching, so it wouldn't be considered a SDS.


Thinking the other thread over further, I see your point about the neutral paralleling, I think you just cited the wrong code to make the point. If one panel had a neural issue like say a loose lug, it could likely use the backup inlet neutral and melt it down. I'm just looking for the correct code citation that would prohibit that install.

 

[wwhitney]

My thought is to back feed my main panel out of the essential loads panel using a manual transfer interlock in the main panel

If you do this, you add a pair of ungrounded conductors from a breaker in the essential loads panel to the interlocked, backfed breaker in the nonessential panel, and that works for the ungrounded conductors. But what do you do with the neutral (grounded) conductor?

If you similarly run a neutral conductor along with the ungrounded conductors, you've now created a permanent neutral conductor loop: meter - ATS - essential loads panel - non-essential panel - meter. That would be a violation of, among other things, the parallel conductor rules in 310.10(H).

Whereas if you don't run a neutral conductor along with the ungrounded conductors, now you have a violation of 300.3(B), unless your new ungrounded conductors follow the same route as the existing neutral conductors. Which isn't possible with multiple services as that path goes through the meter.

I have done something similar, but it was all on one service. Instead of the ATS, there's a Tesla Backup Gateway. I ran no additional neutral conductor, to avoid a 310.10(H) issue. And I routed the interlocked ungrounded conductors between the essential panel and the non-essential panel back through the Backup Gateway, following the route the existing neutral conductors supplying each panel take, to comply with 300.3(B).

Cheers, Wayne

 

[jaggedben]

What Wayne explained. Plus 300.20 being another relevant code section if metal raceways are used.

Putting the interlocked circuit back through the same counduit is a good solution if practical, but in this case sounds like it would violate 230.7.