Portable Generator inside Separate building

[marmathsen]

https://i.imgur.com/Wj6rAZG.png

I'm hoping some of you guys and gals can help me figure this out. Attached is an image I drew up of how I THINK it should be connected but please correct me if warranted.

I have a potential customer who has asked me to run a feeder to a detached shop on a residential property - No big deal. Then she tells me that they want me to setup provisions for a portable 7kW generator that will be stored and operated inside the shop and feed back to the main house for backup power. I have spent many hours now trying to get to the bottom of what the NEC requires (I'm using 2017 edition, and I'm in Snohomish County Washington). It is a non separately derived system because the neutral is permanently bonded to utility neutral.

One hangup I'm having is that the generator has a neutral to equipment ground bond that I'm not inclined to disconnect, but by not disconnecting it, don't I create a parallel neutral current path on the raceways and enclosures?

If I do "un-bond" the neutral to EG connection then I'm inclined to say I should dismantle the other 20A GFCIs on the side of the generator because the manual explicitly says they won't function properly if it's disconnected.

Look forward to hearing back from everyone.

Side note - I did express concerns about operating a gas engine inside an enclosed space and she was trying to assure me that her husband will "properly" seal and vent it so it shouldn't be a concern. I will be STRONGLY recommending that they install a CO alarm in the shop.

Rob

 

[zbang]

Ignoring the bonding question, how do you prevent the generator from backfeeding the incoming service?? That's a bit more important than where the SBJ is.

 

[ActionDave]

View attachment 19084 https://i.imgur.com/Wj6rAZG.png

I'm hoping some of you guys and gals can help me figure this out. Attached is an image I drew up of how I THINK it should be connected but please correct me if warranted.

I have a potential customer who has asked me to run a feeder to a detached shop on a residential property - No big deal. Then she tells me that they want me to setup provisions for a portable 7kW generator that will be stored and operated inside the shop and feed back to the main house for backup power. I have spent many hours now trying to get to the bottom of what the NEC requires (I'm using 2017 edition, and I'm in Snohomish County Washington). It is a non separately derived system because the neutral is permanently bonded to utility neutral.

One hangup I'm having is that the generator has a neutral to equipment ground bond that I'm not inclined to disconnect, but by not disconnecting it, don't I create a parallel neutral current path on the raceways and enclosures?

If I do "un-bond" the neutral to EG connection then I'm inclined to say I should dismantle the other 20A GFCIs on the side of the generator because the manual explicitly says they won't function properly if it's disconnected.

Look forward to hearing back from everyone.

Side note - I did express concerns about operating a gas engine inside an enclosed space and she was trying to assure me that her husband will "properly" seal and vent it so it shouldn't be a concern. I will be STRONGLY recommending that they install a CO alarm in the shop.

Rob

Your going down a rabbit hole. The generator neutral needs to be lifted to prevent a parallel path, new ul rules require that they be bonded.

 

[ActionDave]

Ignoring the bonding question, how do you prevent the generator from backfeeding the incoming service?? That's a bit more important than where the SBJ is.

He's got an interlock on the main panel.

 

[marmathsen]

Your going down a rabbit hole. The generator neutral needs to be lifted to prevent a parallel path, new ul rules require that they be bonded.

This statement got me to thinking...In a more simplified installation where you have a portable "bonded neutral" generator feeding into a main panel (and obviously utilizing a generator interlock kit), don't you have parallel paths at that point as well?

Also, 250.34(C) Informational Note states that I should use 250.30 for portable generators supplying fixed wiring systems. But 250.30 is for "Grounding Separately Derived Alternating-Current Systems" and states (250.30 Informational Note No. 1) "...An alternate ac power source, such as an on-site generator, is NOT a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor." Obviously using a basic generator interlock kit ensures a "solidly interconnnected grounded conductor to the system grounded conductor" thereby making it a "non separately derived system". So now I'm not sure if I should be considering a portable generator connected to fixed wiring a separately derived system or not.

 

[zbang]

He's got an interlock on the main panel.

My eyes are getting too old to read small blurry print- looks like a breaker with some fuzz next to it .

 

[ActionDave]

... So now I'm not sure if I should be considering a portable generator connected to fixed wiring a separately derived system or not.

Electrically speaking, there is nothing wrong with an unbonded portable generator, lots of them used to be that way. There is no requirement for a generator to be UL listed. I don't know how many non listed ones are on the market at this time.

The biggest problem with using portable generators is they suck for powering up your house. Sure, they are better than nothing but they are loud, they drink gas, and unless they are above average quality they put out some ugly AC.

Since you are already putting in the same basic infrastructure for a portable genny as a permanent one a real transfer switch and a real generator is not so much of big upgrade.

 

[gadfly56]

Electrically speaking, there is nothing wrong with an unbonded portable generator, lots of them used to be that way. There is no requirement for a generator to be UL listed. I don't know how many non listed ones are on the market at this time.

The biggest problem with using portable generators is they suck for powering up your house. Sure, they are better than nothing but they are loud, they drink gas, and unless they are above average quality they put out some ugly AC.

Since you are already putting in the same basic infrastructure for a portable genny as a permanent one a real transfer switch and a real generator is not so much of big upgrade.

I think you're right. You can get a PowerPact Generac with a 50 amp ATS from HD for $1,877 that's rated for 7.5 kW running on LP, 6 kW running on NG. There is also a Champion product with 8.5/7.5 kW ratings for $1,938. I can't speak to the merits of either one.