Generac 50 amp SMM

[AC\DC]

So customer got a very small back up generator with 200 amp service rated automatic transfer switch. I have yet to size his home working on that but his generator is only 14kw.
Have not used these SMM yet, from reading them there frequency based and in reallity I can hock these up to what ever load I need so the calculated load is never over 14kw. Is that correct.
Just from quick glance I am thinking I need 2 or 3.
One for - Well pump-- heat. rest would just be small loads in home.
Rang and water heater are gas.

 

[electrofelon]

So customer got a very small back up generator with 200 amp service rated automatic transfer switch. I have yet to size his home working on that but his generator is only 14kw.
Have not used these SMM yet, from reading them there frequency based and in reallity I can hock these up to what ever load I need so the calculated load is never over 14kw. Is that correct.
Just from quick glance I am thinking I need 2 or 3.
One for - Well pump-- heat. rest would just be small loads in home.
Rang and water heater are gas.

You probably want the well pump on it no? Sounds like you dont need any at all, I probably wouldnt bother with any shedding at all.

 

[Chamuit]

Agreed, unless the AC heating is electric.

 

[AC\DC]

We don't have AC around here and Heat is electric.
702.4 b 2 states Full load transferred by automatic transfer equipment.
Normally I do remodels so I just use 220.87. This states to determining Service load.
SO I can use the Powercompany highest actual demand as my goal post, Correct.

 

[electrofelon]

We don't have AC around here and Heat is electric.
702.4 b 2 states Full load transferred by automatic transfer equipment.
Normally I do remodels so I just use 220.87. This states to determining Service load.
SO I can use the Powercompany highest actual demand as my goal post, Correct.

Does your POCO measure demand on residential meters?

I am aware of the stupid code requirement to provide a load calc for automatic transfer equipment, but I usually ignore it and use my own judgment, we don't have permits and inspections around here.

 

[Chamuit]

We did the load calcs for the city. Here in CenterPoint's area, you can look at the meters and see the peak load. We always used that to confirm what we were setting in place. Don't forget, if you can manage a (large) load, you usually get away with a smaller unit.

 

[AC\DC]

Does your POCO measure demand on residential meters?

I am aware of the stupid code requirement to provide a load calc for automatic transfer equipment, but I usually ignore it and use my own judgment, we don't have permits and inspections around here.

Yes they do measure Peak demand been nice I got lazy I don't do alot of load calc on remodels just call them.
That section does seem dumb since you can have a manual transfer and bog the generator down just as easy as auto.
I guess they don't want it instantly switching over if the owner does not know the power is out.

 

[AC\DC]

Thank you for the help

 

[LarryFine]

I guess they don't want it instantly switching over if the owner does not know the power is out.

Right. The concern is for loads that can start or restart without human intervention.

It wouldn't do to come home to find burst pipes because the generator shut down.

 

[electrofelon]

Yes they do measure Peak demand been nice I got lazy I don't do alot of load calc on remodels just call them.
That section does seem dumb since you can have a manual transfer and bog the generator down just as easy as auto.
I guess they don't want it instantly switching over if the owner does not know the power is out.

That's nice. None of the POCOs I work with have resi demand meters. Commercial yes. One has it displayed right on the meters as it cycles thru.

 

[VirutalElectrician]

But how useful is peak demand from the meter? How long ago was it? What time period was it averaged over?

That one time back in '20 when someone turned on the oven, ran the AC, sat in the hot tube, demanded hot water, dried their hair, had the plasma cutter running with the compressor and cranked the stereo to 11 can't be all that useful for peak demand.

 

[LarryFine]

But how useful is peak demand from the meter? How long ago was it? What time period was it averaged over?

Isn't peak demand an instantaneous value, not averaged over time?

That one time back in '20 when someone turned on the oven, ran the AC, sat in the hot tube, demanded hot water, dried their hair, had the plasma cutter running with the compressor and cranked the stereo to 11 can't be all that useful for peak demand.

That seems to be the very definition of a peak demand moment.

 

[AC\DC]

Peak demand around here is ussaly lower than if you do standered calculation.
Peak demand is great in my opinion since you know the worst case situation that has happened at that premise.

 

[Chamuit]

Isn't peak demand an instantaneous value, not averaged over time?


That seems to be the very definition of a peak demand moment.

Exactly! You won't get caught with your pants down as the saying goes...

 

[VirutalElectrician]

Isn't peak demand an instantaneous value, not averaged over time?


That seems to be the very definition of a peak demand moment.

You're missing the common sense aspect. Do you plan to handle the peak demand that happened once, or the peak demand that happens once a month? I think most people that have the where-with-all to look in to a generator are also smart enough to know they aren't going to be able to use the hot tub and welder while on generator, at least without not having to pay 3-4x what it would cost to cover their "real life" peak demand.