backfeeding feed-through panel lugs

[dcg9381]

I'm doing something a bit odd due to using a generator ATS and a panel needed upstream of that ATS for solar - IE a panel that is not tied to the generator as we want the solar to drop out when the generator is on.

I'm working with an master electrician, but want to double check him. He had me install a feed-through panel which is fine, but power comes in through the bottom of this panel. That is, whenever the upstream power is on (there is a disconnect upstream), that panel will be hot, even if the main breaker on the panel is turned off.

All the main breaker on that panel will do is shut down power to the ATS (and successive sub-panels).

He says back-feeding a feed-through panel is fine. I can't find anything in code about it or much writing on it at all.. So I want to double check. It seems to me that someone could come along, shut off the main to that panel and think it's no longer hot, which isn't the case...


One alternative would be to back-feed it through a labelled breaker that is installed with a clip...

 

[grounded-b]

I'm doing something a bit odd due to using a generator ATS and a panel needed upstream of that ATS for solar - IE a panel that is not tied to the generator as we want the solar to drop out when the generator is on.

I'm working with an master electrician, but want to double check him. He had me install a feed-through panel which is fine, but power comes in through the bottom of this panel. That is, whenever the upstream power is on (there is a disconnect upstream), that panel will be hot, even if the main breaker on the panel is turned off.

All the main breaker on that panel will do is shut down power to the ATS (and successive sub-panels).

He says back-feeding a feed-through panel is fine. I can't find anything in code about it or much writing on it at all.. So I want to double check. It seems to me that someone could come along, shut off the main to that panel and think it's no longer hot, which isn't the case...


One alternative would be to back-feed it through a labelled breaker that is installed with a clip...

Feeding a panel via the Bus lugs is code compliant , as long as there is a breaker upstream, sized properly for the panel and feeder wire.

The breaker which usually would be the "Main breaker" in the panel is now being used as a backfed, "feeder breaker" supplying power to downstream panels. This is also fine, as long as the breaker is labeled properly, ie: no longer says "Main", but indicates what loads it serves.

A panel does not always have a main breaker installed. Many panels are installed as "Main Lugs Only" or MLO.

 

[dcg9381]

Feeding a panel via the Bus lugs is code compliant , as long as there is a breaker upstream, sized properly for the panel and feeder wire.

The breaker which usually would be the "Main breaker" in the panel is now being used as a backfed, "feeder breaker" supplying power to downstream panels. This is also fine, as long as the breaker is labeled properly, ie: no longer says "Main", but indicates what loads it serves.

Thanks. This one has a main installed (limited options in 200A panels with low number of breakers, feed-thru lugs). I'll re-label it.

NEC drives me crazy some times... Stuff like this seems like a hazard to me (as the panel breakers are hot if the main is off), yet so over-protective elsewhere...

 

[grounded-b]

Thanks. This one has a main installed (limited options in 200A panels with low number of breakers, feed-thru lugs). I'll re-label it.

NEC drives me crazy some times... Stuff like this seems like a hazard to me (as the panel breakers are hot if the main is off), yet so over-protective elsewhere...

The panel has no MAIN. It is now a breaker protecting a feeder to your ATS.

Why don't you keep the "Main" breaker as a disconnect for the panel ( forget about the feed-thru lugs ) and add another large breaker to feed the ATS? Cost savings?

 

[dcg9381]

The panel has no MAIN. It is now a breaker protecting a feeder to your ATS.

Got it.
The "main" (bonded neutral and ground) is 250' away.

Why don't you keep the "Main" breaker as a disconnect for the panel ( forget about the feed-thru lugs ) and add another large breaker to feed the ATS? Cost savings?

The main has a disconnect, but it's 250' away. I need a panel with a few breakers near the ATS/generator that is not fed by the generator. I'll eventually add an additional breaker for PV solar, as I cannot feed solar into a panel that is fed by a generator.

 

[grounded-b]

Got it.
The "main" (bonded neutral and ground) is 250' away.

No, that is not your "Main", that is called the "Service Disconnect". You can only have one "Service Disc.", but, you can have many panels with "Mains" in them. Mains are built into a panel, and disconnect all power to that panel.

 

[wyliesdiesels]

I'm doing something a bit odd due to using a generator ATS and a panel needed upstream of that ATS for solar - IE a panel that is not tied to the generator as we want the solar to drop out when the generator is on.

I'm working with an master electrician, but want to double check him. He had me install a feed-through panel which is fine, but power comes in through the bottom of this panel. That is, whenever the upstream power is on (there is a disconnect upstream), that panel will be hot, even if the main breaker on the panel is turned off.

All the main breaker on that panel will do is shut down power to the ATS (and successive sub-panels).

He says back-feeding a feed-through panel is fine. I can't find anything in code about it or much writing on it at all.. So I want to double check. It seems to me that someone could come along, shut off the main to that panel and think it's no longer hot, which isn't the case...


One alternative would be to back-feed it through a labelled breaker that is installed with a clip...

NEC code is permissive so if you dont find anything that says you cant do such and such, youre good to go

 

[dcg9381]

No, that is not your "Main", that is called the "Service Disconnect". You can only have one "Service Disc.", but, you can have many panels with "Mains" in them. Mains are built into a panel, and disconnect all power to that panel.

Got it.. Thanks for the nomenclature.

NEC code is permissive so if you dont find anything that says you cant do such and such, youre good to go

I know, and I've argued that myself on a few things, but in this particular case having a "live" panel essentially fed backwards with a non-obvious service disconnect made me wonder if my advice was wrong. Appreciate you guys weighing in and letting me know I wasn't being steered wrong.

 

[ant.foste]

I would suggest a bold sticker stating that panel is fed from multiple sources.

 

[PCustoms]

OP, can you post a pic?

I'm confused but your description, sounds like the label does have a main breaker, but you are still feeding in from another location. Not quite understanding how this is interlocked to prevent a back feed situation.

 

[kaffine]

Why not feed the panel through the main and have the ATS connected to the lugs?

 

[dcg9381]

I would suggest a bold sticker stating that panel is fed from multiple sources.

It's only fed from once source, the feed-thru legs. But I'll mark that main breaker as "not a panel disconnect".

 

[dcg9381]

Not quite understanding how this is interlocked to prevent a back feed situation.

Solar shuts down whenever the grid fails.. All grid tie solar is designed this way to prevent back feeding the grid unexpectedly.

I've attached a basic diagram.

 

[ant.foste]

Solar shuts down whenever the grid fails.. All grid tie solar is designed this way to prevent back feeding the grid unexpectedly.

I've attached a basic diagram.

Thanks for the drawing. Worth 1,000 words.

I don't do residential. So this setup isolates solar and utility on the norm side of the ATS, and put some generator power to the emer path through thenATS, powering only those circuits which run through the sub panel. That's the intent here? Why not a configuration in which the entire house is powered from the generator?

Edit: My experience with residential solar is through research only. However, I spend a lot of time on utility scale solar farms during construction and commissioning. My understanding of residential solar is the invertor stops the through flow when AC buss voltage is lost, hence preventing a backfeed scenario to a dead grid. Is that not the case? Or, does your invertor not have that capability?

Maybe I'm not understanding why the ATS is not being located before the main panel.

 

[dcg9381]

Thanks for the drawing. Worth 1,000 words.

I don't do residential. So this setup isolates solar and utility on the norm side of the ATS, and put some generator power to the emer path through thenATS, powering only those circuits which run through the sub panel. That's the intent here? Why not a configuration in which the entire house is powered from the generator?

The intent here is to have PV solar that feeds the grid (and the house), but still retain the emergency power feature of the generator. It's necessary to configure this way so the PV solar doesn't stay "on" when the generator fires up. A potential back-feed to the generator can occur if we are not using all of the PV power at the house.

The house is 100% generator powered. The house is the "Res. sub panel" - it's actually a series of sub panels that serve as load centers for the residence.

My understanding of residential solar is the invertor stops the through flow when AC buss voltage is lost, hence preventing a backfeed scenario to a dead grid. Is that not the case? Or, does your invertor not have that capability?

As far as I know, all grid tie solar setups must disconnect when the grid goes down. You have it correct.

Maybe I'm not understanding why the ATS is not being located before the main panel.

The service entrance is 250' feet away or so, which is part of it. The other part is that PV solar MUST be electrically "up stream" from the ATS. Remember, the ATS is a switch, so if the generator is active, it is the service entrance and the remaining side is dead.. That renders the panels (and solar) up stream of the ATS dead and nothing gets back-fed by solar.

The panel required upstream of the ATS is a "feed in" panel - it's really not a load panel - it's purpose is to house a breaker for solar... Any load I connect to it won't be backed up by the generator.

 

[wyliesdiesels]

The intent here is to have PV solar that feeds the grid (and the house), but still retain the emergency power feature of the generator. It's necessary to configure this way so the PV solar doesn't stay "on" when the generator fires up. A potential back-feed to the generator can occur if we are not using all of the PV power at the house.

The house is 100% generator powered. The house is the "Res. sub panel" - it's actually a series of sub panels that serve as load centers for the residence.





As far as I know, all grid tie solar setups must disconnect when the grid goes down. You have it correct.




The service entrance is 250' feet away or so, which is part of it. The other part is that PV solar MUST be electrically "up stream" from the ATS. Remember, the ATS is a switch, so if the generator is active, it is the service entrance and the remaining side is dead.. That renders the panels (and solar) up stream of the ATS dead and nothing gets back-fed by solar.

The panel required upstream of the ATS is a "feed in" panel - it's really not a load panel - it's purpose is to house a breaker for solar... Any load I connect to it won't be backed up by the generator.

the grid tie systems with a tesla power wall do not disconnect the PV inverter when the grid goes down...

 

[dcg9381]

the grid tie systems with a tesla power wall do not disconnect the PV inverter when the grid goes down...

Right because the PV inverter feeds the batteries, not the grid. My guess is that there is a transfer switch which prevents feeding back from the batteries to a dead grid, but I've never installed one... Generators are cheaper for "emergency" and power walls - it's hard to get them to pay back unless you're on variable rate power.