Question on whole house generator with ATS and 2008 Code

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Old 02-21-10, 06:17 PM
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Question on whole house generator with ATS and 2008 Code

I live in NJ which is now on the 2008 code.

I just built a new house with a 200 amp service, SqD Homeline panel.

The house is 3,400sqft with 3 separate central AC units.

I know I'm a little late, but I would like to install a generator and ATS. I would like it for lighting, fridgerator, television, and well pump. Sometimes I'm on the road for a couple days so I need an ATS incase the power goes out and my wife is home alone. I'm thinking a 10KW would be a good size.

I do not expect the generator to run the AC units, but with the 2008 code what options do I have? I would have to replace my brand new panel with a new load sheding model?

What are my options?
 
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Old 02-21-10, 08:49 PM
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I can't help you much on the 2008 code requirements concerning generators (2008 code not accepted here yet), but here is something to think about. You listed what you'd like to back up, but you didn't mention any furnaces. Assuming your heat is gas, I'd certainly think you would want to have heat in the even of a power failure during the winter. Also, how many H.P. is the well pump? Be sure you get a generator big enough to start and run the well pump motor and any other critical motor loads. I was just assuming your heat and hot water was gas when you stated you had 3400 sq ft and only a 200 amp service.
 
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Old 02-21-10, 09:28 PM
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The simplest will be a second panelboard containing all the circuits that you want to be run from the generator. Probably a 125 ampere panel would be sufficient and it would be fed from the Service panel through the automatic transfer switch. Isolation switches and a manual bypass around the ATS may be required; they would definitely be a plus for servicing the ATS.
 
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Old 02-21-10, 09:39 PM
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I am not too famauir with NJ local codes however I can address the NEC verison to suit your situation.

If you going with ATS there is two options you can do from this part.,

Whole house system that will get pretty expensive and it will have to sized to match the main OCPD like your case it is 200 amp so the size of generator is 48Kw and that is very expensive option however there is other option read on .,,

ATS on subpanel you can able get it smaller generator set up or go with MTS either way it will work with the set up.

Before you actaually do this check with your local inspector I am pretty sure someone in your area will chime in with the codes so they can give you the proper way to set up it correct.

Merci,Marc
 
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Old 02-22-10, 06:21 AM
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Thanks for the replies guys!

Yes, the house is natural gas for the 3 forced hot air systems, stove/oven, and water heater.

One concern I have is to separate the AC from the heat. I would need a way to run the heat while also making sure that the AC doesn't come on, which could be problematic since they are the same units. I could install contactors on the outside condensing units, but that would still allow the system to call for the units to come on which could damage something. Maybe this should be done on the low voltage control side.

Even then, i would still need to cut out other circuits to bring the load down to what the generator could handle. So the best option is to just move all the required circuits to a second panel and have the ATS in between?

Originally Posted by french277V View Post
Whole house system that will get pretty expensive and it will have to sized to match the main OCPD like your case it is 200 amp so the size of generator is 48Kw and that is very expensive option however there is other option read on .,,

Merci,Marc
Marc, AFAIK 2008 says that the generator has to be able to handle the calculated load, not the OCPD. Still, the calculated load is way more than I'd like to power
 
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Old 02-22-10, 08:04 AM
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DO you have geothermal heat pumps? because you said you had gas heat? and the furnace and outdoor unit are not linked together as far as power goes....ever that i have seen the only connection is a low voltage wire that controls the outdoor unit

what you could do possibly is install 3 NC normally closed relays on the condenser low voltage lines and run them back to the generator panel put a 24volt transformer before the auto transfer switch so when the generator is putting out power the relays will open causing the condensers to not run!

Ben HVAC-R tech
 
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Old 02-22-10, 02:16 PM
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Originally Posted by braether3 View Post
DO you have geothermal heat pumps? because you said you had gas heat? and the furnace and outdoor unit are not linked together as far as power goes....ever that i have seen the only connection is a low voltage wire that controls the outdoor unit
No, I have natural gas forced hot air.

The outdoor condensing units are powered separately than the indoor units, but I would still have to make sure that the system -can't- call for AC, even if I take the outdoor units out of the equasion.
what you could do possibly is install 3 NC normally closed relays on the condenser low voltage lines and run them back to the generator panel put a 24volt transformer before the auto transfer switch so when the generator is putting out power the relays will open causing the condensers to not run!

Ben HVAC-R tech
That would work too, but I wouldn't want to air handlers inside to try and turn on during the Summer. I would have to find a way to make sure that the AC never comes on without effecting the heat, since I would like that to be able to work.
 
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Old 02-22-10, 02:43 PM
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Originally Posted by VoltageHz View Post
Marc, AFAIK 2008 says that the generator has to be able to handle the calculated load, not the OCPD. Still, the calculated load is way more than I'd like to power
The calculated load would be the load of the smaller sub panel. There is no requirement that the generator has to carry the entire house.

Here is a good video that I this shows exactly what you want:How to Install a Stand-by Generator | Video | Electrical | This Old House

Also search "generator transfer panel" (no quotes)
 
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Old 02-22-10, 02:46 PM
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Having the condensing units (outdoors A/C units) powered from the "utility only" panel would preclude them from ever coming on during a power outage. The blowers in the inside unit coming on during a power outage is really a non-issue because of their size but if you are really concerned an interlock with the condensing unit would be fairly easy to design and install.
 
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Old 02-22-10, 03:20 PM
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yes with a 10 KW genny or bigger you would have almost no issue IF the air handlers got turned on the motors are quiet small easy starting and newer ones are more energy eff.
 
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Old 02-22-10, 03:23 PM
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It won't hurt anything to have the system running without the condensing units on? I ask because the power might go out when we are not home and it could run in this condition for many hours.

Thanks for all the help guys!
 
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Old 02-22-10, 03:31 PM
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nope wont hurt a thing...if it was very hot out it would actually keep air moving in your house

only thing that runs is the blower in a air handler during a call for cooling
 
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Old 02-23-10, 09:34 AM
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Excellent, thanks again!

Is there any online calculator to do a load calculation on a house?

I need to size the generator. I would like to get as many circuits on the generator panel as possible, except for the AC units.
 
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