Two whole house generators?

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Coppersmith

Coppersmith

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Location
Tampa, FL, USA
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Electrical Contractor
I'm subbing to a GC to install wiring to a whole house generator. The GC was planning on purchasing a 48Kw. Now the HO says they want two smaller generators instead. I don't know why. This is really going to complicate matters. Rough guess, my estimate triples.

I assume this is code compliant since I've worked on a job where we installed multiple generators at a hospital although I was not privy to the plans. I just did what they assigned me. I'm assuming each generator would have to power a separate (set of) panel(s). (There are three). I'm assuming there is no way to parallel/sync generators in the 20-24Kw category. Anybody have any experience or code references to offer?
 
I don't see why they would want to paralell 2 gensets, that would be expensive just for the gear it would take.
If they want 2 separate gensets for 2 separate loads they're gonna need 2 transfer switches too.
 
Maybe they're not really paralleling them in an electrical sense.

Could be one for 'critical' circuits (freezer, sump, fridge, furnace etc.) and another for 'luxury' circuits (TV, computer, lights).
 
480sparky said:
Maybe they're not really paralleling them in an electrical sense.

Could be one for 'critical' circuits (freezer, sump, fridge, furnace etc.) and another for 'luxury' circuits (TV, computer, lights).
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In which case you should really also include switching so that if only one generator is operable it can power the critical circuits?
 
445.18(C) , but it doesn't explain how to parralel them, so i guess my first stop would be the manufacturer

~RJ~
 
480sparky said:
Or they just feed two panels through two transfer switches.
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Wouldn't that produce a fixed association between one generator and one panel? That is what I want to avoid in case one generator fails and one panel has all the critical loads.

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GoldDigger said:
Wouldn't that produce a fixed association between one generator and one panel? That is what I want to avoid in case one generator fails and one panel has all the critical loads.

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Click to expand...

I'm addressing what the OP's HO is wanting. Not what you want.
 
48KW for a house ????

I'm guessing 10,000 sq-ft house. Swimming pool. Electric dryer / oven / cook top...
Electric heat as well ????

Something is seriously wrong if this house isn't a mansion.
 
Let me clarify a few things:

Originally the HO wanted a generator large enough to fully replace their entire 200 amp service if there was a power failure. (Yes it's a mansion, Yes they are rich people. Yes it's strange they only have a 200 amp service.) The GC sold them on a 48Kw and asked me to do an estimate for wiring. That was a couple of months ago. Now I just heard they want two smaller units instead. I have not conferred with them so I don't know why.

My assumption is they still want 100% power replacement, not a spare generator, so I think both generators will always be operating simultaneously. As far as I know there is two ways to do this: (1) each generator powers a separate set of panels; or (2) the generators are paralleled/synced and power all the panels. The question about paralleling was mine, not the HO. I don't think they have considered what is needed to have multiple generators.

So to reiterate my original questions:

Code compliant to have multiple generators?

Am I correct that multiple generators can used by powering separate sets of panels?

Is there a way to parallel these generators? (This would help me avoid running new individual feeders to each panel.)

Anybody have any experience or code references to offer?
 
Forget it. You do NOT need a 48KW gen set. No way, no how.

I did a 4500 sq-ft house. 200 amp service was existing.
Changed everything to LED
8 tons of A/C.
Changed a few appliances to energy star.

90 amps was the most the house ever drew. Ever. I had the meter on there for days.
22KW Generac can handle the entire house, no matter what any one says.

Want to get fancy, install a few load shedding devices on the pool sub panel.
 
You will only get about 36 kw off of the panel so oversizing the generator by 30% is waste.

In any event, I suggest using separate panels for each generator and a separate ATS for each panel. If there is a generator failure, switch it out manually. It's a messy process for existing structures but it is the best alternative.

What makes more sense to me, and what I would do, is use a single whole house generator on an ATS. Use a much smaller generator as a backup and wire it in with an MTS and separate overload protection.

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spark master said:
48KW for a house ????

I'm guessing 10,000 sq-ft house. Swimming pool. Electric dryer / oven / cook top...
Electric heat as well ????

Something is seriously wrong if this house isn't a mansion.
Click to expand...
I have one house I wired that has ~60 kW of electric heat installed. Not a super big mansion, but still a pretty big house. Doctor lives there. HVAC guy was one that pushes heat pumps pretty hard, guy didn't want them, electric heat only is simpler and doesn't break down as much, even though heat pumps likely would made a big difference on electric bill. Owner also scared of gas, didn't want any gas in the house. Did end up with a gas fireplace though, but wanted as minimal amount of gas line in the house as possible for it. My thoughts were if one inside fitting springs a leak it won't matter if there is three feet or 100 feet of line in the house.

Coppersmith said:
Let me clarify a few things:

Originally the HO wanted a generator large enough to fully replace their entire 200 amp service if there was a power failure.
Click to expand...
What is the connected load to the 200 amp panel though? I have 200 amps service but actual load probably seldom goes over 50-60 amps, and even when at that level is never there for very long.
 
Coppersmith said:
Let me clarify a few things:

Originally the HO wanted a generator large enough to fully replace their entire 200 amp service if there was a power failure. (Yes it's a mansion, Yes they are rich people. Yes it's strange they only have a 200 amp service.) The GC sold them on a 48Kw and asked me to do an estimate for wiring. That was a couple of months ago. Now I just heard they want two smaller units instead. I have not conferred with them so I don't know why.

My assumption is they still want 100% power replacement, not a spare generator, so I think both generators will always be operating simultaneously. As far as I know there is two ways to do this: (1) each generator powers a separate set of panels; or (2) the generators are paralleled/synced and power all the panels. The question about paralleling was mine, not the HO. I don't think they have considered what is needed to have multiple generators.

So to reiterate my original questions:

Code compliant to have multiple generators?

Am I correct that multiple generators can used by powering separate sets of panels?

Is there a way to parallel these generators? (This would help me avoid running new individual feeders to each panel.)

Anybody have any experience or code references to offer?
Click to expand...


Yes it is code compliant.

Yes use separate transfer switches with separate subpanels...

No, there is not any equipment for paralleling small gen-sets...

I was involved with an install with 3-20KW Kohler gensets...6000 gallons of propane buried in the ground.

The owner with the 3 gensets could run 1, 2 or all 3 generators, thereby saving full if they did not need to power all sections of the place.Gen-1 was the more critical circuits such as heat, and refrigerators, etc...
 
shortcircuit2 said:
Yes it is code compliant.

Yes use separate transfer switches with separate subpanels...

No, there is not any equipment for paralleling small gen-sets...

I was involved with an install with 3-20KW Kohler gensets...6000 gallons of propane buried in the ground.

The owner with the 3 gensets could run 1, 2 or all 3 generators, thereby saving full if they did not need to power all sections of the place.Gen-1 was the more critical circuits such as heat, and refrigerators, etc...
Click to expand...

Thank you.
 
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