One or two transfer switches?

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  #1  
Old 10-16-20, 02:33 PM
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One or two transfer switches?

Here's my situation. I am in finals tages of connecting backup gen to the house panels.
I have 2 200 Amp panels.
HVAC is split between the 2.
I have Generac 20Kw generator. It came with 200 amp automatic switch.
I bought 2nd one, as electrician intended to connect both of them, one per panel.
2 electricians told they will connect both panels, each onto panel feeding wire.
One told me, he will rewire HVAC onto single panel, "whatever I do not need", will go onto the other panel and, only one switch installed.
Who's right? It's nice to have both panels connected, right? Our chances of running ALL appliances same time are, also, slim to none. We are frugal on electricity use.
Also, it sounds more expensive, to have re wiring done, more labor.
Thoughts?
 
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Old 10-16-20, 03:59 PM
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So then you have a 320-400A service in your house ?
Is this being inspected ?
Most inspectors will balk at a 20k generator on a 400A service without using load shedding.
Inspectors in my area won't approve a generator install without a load calculation form submitted.

You have to make sure that your generator can handle whatever is connected to it.
Keep in mind that it will be automatic. You won't be home to shed loads so when the transfer happens.... the generator must be able to handle that load or it's breaker will trip.

 
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Old 10-16-20, 04:20 PM
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Noted.
No one, and I spoke with about 5 electricians by now, even mentioned this. Generator was recommended by electrician that does them.
And how much is load shedding?
 
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Old 10-16-20, 04:22 PM
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If you have the need for 2 200 amp distribution panels, why did you get a automatic switch rated at 200 amp? Does it have something to do with the capacity of the generator? I think you need the service of an electrical engineer to insure all the things you want to accomplish can be done in a safe manner not only for you, but the next owner should you sell your home.
 
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Old 10-16-20, 04:24 PM
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Oh, so it's just the way it's wired and how control panel handles it. Well, hopefully, brand new Generac will be smart enough.
 
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Old 10-16-20, 04:27 PM
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Donno. electrician, who was supposed to do install, pointed and said - buy that. So I bought it. He also said - get 2nd switch. So I did.
HVAC is split between 2 panels. 2 panels = 2 switches?
He had same generator installed same way - with 2 switches - at buddy's house. Passed inspection flying colors. And his house is much larger than mine.
 
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Old 10-16-20, 04:52 PM
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Ukrbyk, its not the size of the house that determines the rating of electrical panels and standby generators but by the real/ planned electrical loads in the house/garage. As someone has already pointed out, a load calculation is usually required by the AHJ for generator/automatic switch install. Did the electrician do one for your home? Is this being done without a permit?
 
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Old 10-16-20, 06:05 PM
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I have it answered.
2 switches.
 
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Old 10-17-20, 04:48 AM
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The generator's automatic control for loss/return of power connects to only one automatic transfer switch. Therefore the 2 automatic transfer switches must be connected to look like one switch to the generator circuit. Does your electrician have the experience to do this? Being a non standard install, Generac may not stand by the warranty for the generator or switches. Good luck.
 
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Old 10-17-20, 07:09 AM
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Thank you. Appreciate good wishes.
 
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Old 10-18-20, 09:23 AM
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Just for readers info.
Talked to buddy or mine, who has identical generator installed with 2 switches. Hardware is identical to mine.
His house is 200sf larger than mine. His entire heating is electric only. What is guaranteed to have higher load, than mine, as I have heat pump and air handler, instead of electric heaters.
He had EVERYTHING turned on and running off that generator. All lights on, heat full blast on both floors, everything electric was on. 20Kw didn't even sneeze.
Now, the install itself.
Apparently, commonly done with 2 switches.
I think, good description is here:

Im installing a 20kw generator with two service rated transfer

Electrician: Jason
Jason :Hello. Thank you for asing your question on Just Answer...
Jason :You would want both panels to come online with generator power at the same time, so wire them in parallel. But I'm curious as to why you would need two transfer switches, unless one panel is not a subpanel fed from a main panel.
Jason :Typically, when a residence has two panels, one would be a main panel, and it would have a breaker in it that feeds a subpanel.
Customer: Correct one utility meter with two breaker panels. If wired in parallel should I be concerned with crossing phases on the utility sensing wires (n1 & n2) also would the 12v battery be over charged with current supplied from two switches.
Jason :You should definitely pay attention to the possibility of cross phasing. You can avoid that by taking voltage readings on the wires coming from each switch. If you get a zero volts reading when reading across one wire from each switch, then those two wires are on the same leg.
Jason :As for overcharging the battery, you should be able to just use the wires from one transfer switch for the battery charger, and cap the other set off.
Customer: Can you tell me what connections are necessary to make the second transfer switch operate. Will the utility sensors still be needed on the second switch and what wires will be needed on the low voltage side dc common, 12v + 193 and transfer.
Jason :You should connect the second switch the same as the first one, as though the first one doesn't exist. At the termination points in the generator, where the transfer switch control wires terminate, you will have two sets instead of one.
Jason :I don't think the second switch will transfer without the utility sensors in place, so I suspect you need them.
Customer: Wow that seems too easy! Maybe I was over thinking this one! I'll make the connections paying attention to the phases on the utility sensor thanks
Jason :You are most welcome. Is there anything else I can do for you at this time?
Jason :If not, I would appreciate an update on your progress when you get a chance, as this is a somewhat complicated installation. No pressure, but even if you Accept now, we can talk more later about this question.
Customer: Takecare

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