Generator load shedding

[MNSparky]

We just starting selling and installing generators so excuse me if this question seems basic. I have a customer that does not want load shedding. He wants us to put in a 26kw generator to feed his 400amp service. The house is still under construction so I haven't been able to solidify what loads he's going to have so I haven't been able to do a load calc, but I'm going to guess it's going to be more than 26kw.

My question is, are we required to put in load shedding or would this be a legal install? I see nothing about it in the NEC. I realize it's not the best idea.

We are on the 2023 NEC here.

 

[LarryFine]

The house is still under construction . . .

Perfect! Now is the time to sort circuits by need to have only one panel on the generator.

Sit with the customer and make three lists: Must haves, Definitely nots, and Optionals.

Then go through the Optionals after you see how full each panel will end up being.

 

[hillbilly1]

The customer wants to run everything? Or too cheap to do load shedding? Modern load shedding can pick and choose loads that are not as important, until generator load drops below a certain point. Otherwise, as @LarryFine suggested, would be required.

 

[retirede]

Automatic or manual transfer switch?

 

[MNSparky]

Unfortunately the house is in between the rough-in and finish stages. It has been wired (by others), insulated, sheetrocked, and painted with knockdown ceilings. The breakers aren't in and and the panel isn't labeled yet. I asked the homeowner for a list of major electric appliances going in but he has yet to get it to me. Walking around, I see there is an electric range, convection/microwave combo, electric water heater and two ACs roughed in.

The house is shaped like a U with a pool going in open space in between wings. There is a 200amp panel in the middle of each leg of the U, neither are on an outside wall. Second floor above both. Slab on grade house, no basement. The service with service discos is on the end of one of the legs and that is also where the generator is planned to go. Getting a load shedding conduit to either panel would involve a lot of sheetrock cutting. The homeowner does not want to do this, that's why he wants to skip the load shedding.

 

[MNSparky]

Automatic or manual transfer switch?

Automatic

 

[LarryFine]

The homeowner does not want to do this, that's why he wants to skip the load shedding.

Then you need a generator and two ATSs with the capacity of the entire calculated load.

 

[MNSparky]

Then you need a generator and two ATSs with the capacity of the entire calculated load.

Yes, that's how I feel as well. Just so we are on the same page, 702.4(A)(2) applies to this situation, correct?

 

[LarryFine]

Yes, that's how I feel as well. Just so we are on the same page, 702.4(A)(2) applies to this situation, correct?

My '17 NEC doesn't have that section. What does it say?

 

[jaggedben]

.... Walking around, I see there is an electric range, convection/microwave combo, electric water heater and two ACs roughed in.

...

Those things by themselves sound like they would possibly not exceed 26kW using the optional method. (220.82)
However...
What about the dryer? Oven? Is there going to be an EV charging circuit?
Not that I see any justification for a 400A service so far but 26kW is only 108A.

My speculation aside...
The bottom line is that unless/until you can do a load calc to prove the load is under 26Kw then you don't have a legal install without load shedding.

 

[jaggedben]

Yes, that's how I feel as well. Just so we are on the same page, 702.4(A)(2) applies to this situation, correct?

Yes.

 

[LarryFine]

What about the dryer?

Dryers need not count because they won't restart automatically.

 

[jaggedben]

Dryers need not count because they won't restart automatically.

I wish 702 said that but I have seen that it does.

 

[Seven-Delta-FortyOne]

The load shed device from Generac, the SMM, is very simple to install, and
does not necessarily shut the load off altogether, only when there is insufficient power to run it.

I know Briggs and Stratton has one that functions identically, and I believe Kohler does as well, but I haven’t installed a Kohler one.

Why do they not want load shed?

 

[LarryFine]

Why do they not want load shed?

My guess is they want to be able to live like the utility power is still on.

 

[electrofelon]

It will probably be totally fine with no load shedding, and I would install it and not worry about it one single bit here in upstate New York where there really aren't permits and inspections. Of course if you are in a more strict area, the NEC says it needs to meet the calculated load. I agree with others that a few loads shed modules is probably all you need Does the POCO there measure demand on resi accounts? If so you could "not commission" the generator (wink wink ) and see what the measured demand comes in at which should give you the green light.

Light generator loading drives me crazy. Building I'm in right now, well there are three buildings on a 150kw set. Feeds like seven 200 amp and 5 100 amp panels (120/208 three phase). The generator feeder is only halfway loaded, we're getting there, load it up!

 

[Seven-Delta-FortyOne]

My guess is they want to be able to live like the utility power is still on.

And most of the time they will. Hot tub will shut off while they’re cooking and running laundry, and at night the car will charge and the hot tub will reheat.

Or they can step up to a liquid cooled like the big boys.

 

[Birken Vogt]

I have a customer that does not want load shedding. He wants us to put in a 26kw generator to feed his 400amp service.

My question is, are we required to put in load shedding or would this be a legal install? I see nothing about it in the NEC. I realize it's not the best idea.

We are on the 2023 NEC here.

Why is the customer dictating what size generator AND what he wants to run? Seems it should be one or the other.

The generator must be able to handle the connected load in accordance with article 220 calcs or "another approved method"

 

[Dsg319]

Isn’t there wireless load shed modules available nowadays?

 

[MNSparky]

Sorry, had to be away from the computer a while, I'll try to answer everyone's questions.

We are a Kohler dealer, Kohler doesn't do wireless load shed modules. We have to get wiring from the transfer switch to the panels for the load shedding. The only thing that we can shed without cutting up a ton of sheetrock is the pool equipment, which will be right next to the generator.

The customer keeps telling me that there will be only 2 people living in this huge house so he doesn't feel that he needs anything bigger than a 26kw. He's probably right, but the code doesn't care how many people are in the house. I guess I'm fine installing it without load shedding, I just don't want to fail the inspection due to it and then have a mess on my hands. This area is pretty strict. I'm going to call the inspector this morning and discuss this with him.