Two Generators One Service

[mkgrady]

This is a large home where the customer has a 400 amp service and two 200 amp MCB panels off the meter. I can't think of any code issue with installing two generators and two 200 SE rated transfer switches (ATS'S). At this point the plan is to use 2-20KW generators.

The point of using two generators is to conserve propane. He wants to be able to power most things in the house when there is reason to believe the outage will be brief enough that he will not run out of propane before power is restored. If the duration is long or looks like it could be he wants to shut off the less essential generator to conserve fuel.

So in this case I would put the most essential loads on generator 1 and MCB panel 1, and I would put less essential loads on generator 2 and MCB panel 2. That still leave lots of non essential loads on each panel that are too large for the generator output. The plan for that is to use load shed relays. The typical generic units allow for controlling two AC systems and up to four additional large loads.

I figure out of the 80 or so branch circuits I will wind up moving about half of them to the correct panel. That will be a lot of work that I wish could be avoided. The space needed for all the hardware required also concerns me but I think is doable.

Any thoughts on code issues or a better way to plan this job would be appreciated. Thanks

 

[texie]

This is a large home where the customer has a 400 amp service and two 200 amp MCB panels off the meter. I can't think of any code issue with installing two generators and two 200 SE rated transfer switches (ATS'S). At this point the plan is to use 2-20KW generators.

The point of using two generators is to conserve propane. He wants to be able to power most things in the house when there is reason to believe the outage will be brief enough that he will not run out of propane before power is restored. If the duration is long or looks like it could be he wants to shut off the less essential generator to conserve fuel.

So in this case I would put the most essential loads on generator 1 and MCB panel 1, and I would put less essential loads on generator 2 and MCB panel 2. That still leave lots of non essential loads on each panel that are too large for the generator output. The plan for that is to use load shed relays. The typical generic units allow for controlling two AC systems and up to four additional large loads.

I figure out of the 80 or so branch circuits I will wind up moving about half of them to the correct panel. That will be a lot of work that I wish could be avoided. The space needed for all the hardware required also concerns me but I think is doable.

Any thoughts on code issues or a better way to plan this job would be appreciated. Thanks

I think I would consider using 1 400 amp ats with 2 20 KW gensets in parallel and add load shedding. Until recently this was not possible on small gensets but Kohler seems to have figured out a way to do it at a good price point. Look here: http://www.kohlergenerators.com/home-generators/products/GM85144-KP1-QS

Kind of like a big boy system but on a residential scale.

 

[mkgrady]

I think I would consider using 1 400 amp ats with 2 20 KW gensets in parallel and add load shedding. Until recently this was not possible on small gensets but Kohler seems to have figured out a way to do it at a good price point. Look here: http://www.kohlergenerators.com/home-generators/products/GM85144-KP1-QS

Kind of like a big boy system but on a residential scale.

Im familiar with Briggs and Stratton and Generac but not Kohler. I have heard I can't even start up a Kohler because you need to be a dealer. If that is true, I'm not sure any advantages of the Kohlers running in parallel are worth it. Running small generators in parallel does seem pretty cool but the customer would not even understand it let alone pay for it if it costs more.

 

[ceb58]

I see no problem doing it that way as long as you have sized the generators to the load. The only thing I see that could be a problem is how dose the HO plan on shutting down the "less essential" generator? You would not want him to just turn off the gen. under load.

 

[mkgrady]

I see no problem doing it that way as long as you have sized the generators to the load. The only thing I see that could be a problem is how dose the HO plan on shutting down the "less essential" generator? You would not want him to just turn off the gen. under load.

Good point. Should be unloaded and cooled down I imagine. Any thoughts on how best to do that with a Generac?

And do I also have a problem if he runs out of propane on the remaining unit? I would expect the generator to shut down the moment it runs out of fuel which seems just like shutting it off under load.

 

[hpe1087]

Twin 20KW Gensets

Twin 20KW Gensets

I would be more inclined to install (1) 200A transfer switch per 20KW generator. If a 400A transfer switch is installed, there may be a potential problem if a component fails, inside the 400A transfer switch, causing the transfer mechanism from transferring to generator power. This may leave the customer without "any" power, even though both 20KW generators are running and burning fuel. Having (2) 200A transfer switches may provide some reassurance that some of the emergency circuits will still operate if one of the 200A transfer switch fails to operate properly.

Generac offers an auxiliary contact kit that can be mounted to the transfer switch mechanism. This contact kit can be wired so an indicator light can be activated to let the customer know if one of the transfer switches has not transferred to generator power.

The (2) Generac 200A transfer switches can be linked together with the #23 + #194 control wires to permit simultaneous activation during a utility outage.

 

[kwired]

Good point. Should be unloaded and cooled down I imagine. Any thoughts on how best to do that with a Generac?

And do I also have a problem if he runs out of propane on the remaining unit? I would expect the generator to shut down the moment it runs out of fuel which seems just like shutting it off under load.

Beat me to it, it is going to shut down under load should it run out of fuel or shut down on any safety feature - oil pressure, hi temp, etc. Having that happen only once in a great while is not going to hurt it that much either as far as I know, compared to doing it quite frequently.

 

[mkgrady]

I would be more inclined to install (1) 200A transfer switch per 20KW generator.

Generac offers an auxiliary contact kit that can be mounted to the transfer switch mechanism. This contact kit can be wired so an indicator light can be activated to let the customer know if one of the transfer switches has not transferred to generator power.

The (2) Generac 200A transfer switches can be linked together with the #23 + #194 control wires to permit simultaneous activation during a utility outage.

My plan is to install two 200 amp ATS's

The customer will know if either ATS does not transfer by looking at what has been re-energized during an outage

I don't understand the advantage of linking the two ATS's together. Each gen and ATS will be wired like a single set would.

 

[mkgrady]

Beat me to it, it is going to shut down under load should it run out of fuel or shut down on any safety feature - oil pressure, hi temp, etc. Having that happen only once in a great while is not going to hurt it that much either as far as I know, compared to doing it quite frequently.

I wonder if it would make sense to shut off the generator output breaker before shutting off the generator to let it cool down.. I suppose if they really got concerned about running out of propane they could first shut down the least critical generator and they could also just run the most critical one for a few hours a day.

When I loose power I run the house from a portable butI just shut it off at night even in the winter.

 

[kwired]

When I loose power I run the house from a portable butI just shut it off at night even in the winter.

I run a portable also, I seldom shut it down, it usually runs out of gas first. I am not too concerned about cooling it down before shutting it off. First the only times I have run it as a standby it was pretty cold outside, I doubt it really needed any cooling down. Second, I don't want to go out to shut it down. Summertime outages I have had were not long enough to even justify spending the time getting the thing out and firing it up. It is easier to get by when weather is warm, I could probably go without power for several hours in summer without firing it up but in winter if I know power will likely be out for more than 4-6 hours I am going to fire it up fairly quickly.