9KW NG Generator with 200 amp service-rated ATS

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Old 04-10-13, 06:12 PM
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9KW NG Generator with 200 amp service-rated ATS

I had two different electricians give opposing approaches to my installation request. One said no problem to the set-up and one said that 9KW is not enough for a 200 amp service-rated ATS. He said that I would need a 20KW generator or he would install a 100 amp circuit breaker box to feed 10-12 circuits. He said the risk of overload was too great and it was against national code. My worst-case (large users all on at same time) electrical demands are 2 refrigerators, one 240V oven, and one 8K BTU window AC. I don't have central air, sump pump, pool or electric heat or hot water. My boiler is NG with an indirect HW heater. I have 200 amp service with a 200 amp panel. The house used to have central AC and an electric cook top, but no more. Please give advice. Their quotes were $3000 and $3800 respectively, so that's not an issue. I really don't want a 20KW unit.

Thank you,
Matt
 
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Old 04-10-13, 06:54 PM
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My worst-case (large users all on at same time) electrical demands are 2 refrigerators, one 240V oven, and one 8K BTU window AC. I don't have central air, sump pump, pool or electric heat or hot water. My boiler is NG with an indirect HW heater.
Its emergency power...They all should not be used at the same time IMO. You want to run all at the same time then yeah....20kw-30kw....

The 12 circuit sound like the best option IMO... You may need to run things at various times as not to overload the gen.

example:

Run the two refrigerators for some time then switch off the breaker to them. While they are off possibly cook a meal on the stove. After cooking run the sump. Then run the refrige again for a hour or two.

Take a break and run the A/c or heat to cool off or warm up. Its a balancing act. Its only emergency.

You need to pick those 12 circuits wisely but thats a lot IMO. You can simply plug something into a working outlet if its not on a gen circuit. Coffee maker, toaster, microwave...etc...

I only have 6 circuits and ran a well, heat, lights, tv, ceiling fans, refridge, a/c if needed... But not at the same time. Lighting was always on...everything else was alternated.

I did this all for 9 days during sandy on a 3250 watt gen that sipped gas. Only went through 12 gallons.

Just my opinion....
 
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Old 04-10-13, 06:59 PM
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Thanks for the reply. His concern was having all of the large users on when to initial power outage occurred. I agree with your approach once the house is on generator power. I mostly want to make sure that I'm not violating an electrical code.
 
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Old 04-10-13, 07:25 PM
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I would forget about having an ATS. You have to go out and start and plug in the gen right? How do you thin a will an ATS work for you?

What gen do you have?
 
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Old 04-10-13, 07:25 PM
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Matt...... It has come to the point where the local jurisdictions are looking pretty heavily at generators. They are requesting a load calculation. Actually.....it's not a request.... it's mandatory. I've had inspectors come in to our jobs and do their own load calculations. We just finished a residential installation with a 48kw Kohler propane on a 400 amp ATS. The inspector checked almost every load.

Using a 9kw generator on a 200amp ATS is not the issue. The issue is if you aren't home and you lose power. The generator will be forced to run the entire house load....or at least any device that may be running at the time.

In your case it doesn't sound like you would have that issue but you can still overload your generator. I know.....you know what to do if there is a power failure.......you conserve. However....the inspectors do not look at it that way. Their view is that the consumer is not aware of maximum allowed wattage and therefore must be protected from overloading the generator.

So basically your first electrician is correct.

You could have a manual transfer panel installed but it will not transfer automatically if you aren't home. If you are using a Generac...... their ATS has load shedding management in it. Have the electrician add in a load shed module for your range.

Have the electricians done a load calculation. You could actually do it yourself. A little tricky. I could help if you have any questions.

The load calc sheet is on page 18 in the link below.
Generac generator load calcs
 
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Old 04-10-13, 07:59 PM
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Thanks very much. The ATS that I'm considering does have the smart technology. When I asked about DLM's, the one that didn't want to use the 200 amp ATS said that he had too many issues with them and would not use them. They did not do a formal load calculation. You're right, when I'm not home, my dryer and oven are not going to be on. How big of a problem is it when an overload occurs? Are there fuses and circuit breakers in the Generac that blow?
 
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Old 04-10-13, 08:09 PM
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The generators have a circuit breaker that will protect it.
 
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Old 04-11-13, 09:49 AM
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Another thing to keep in mind is when you have an ATS, you probably won't know the power is out. Your best bet would be to install a 100A subpanel with select loads if you're not going to get a 20KW generator.
 
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Old 04-11-13, 08:21 PM
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One said no problem to the set-up and one said that 9KW is not enough for a 200 amp service-rated ATS.
The size of the service you are backing up with a 9 KW genset and ATS isn't the issue, the issue is the load. The NEC requires that an automatic transfer switch and standby generator must have sufficient capacity to power the ENTIRE calculated load OR have load shedding capability. As was already stated, you may not be home when normal power is lost and the generator starts.
 
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Old 04-11-13, 09:49 PM
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The solution to your problem is simple really. Do a load calc to determine what the minimum size gen you need with an ATS. If the load calc is greater than 9kw either install a larger generator, load shed, or use a manual transfer switch. Those are your options period
 
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Old 04-13-13, 01:08 PM
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An auto-start generator that starts and checks itself once a month, connected through an ATS, is the way to go, IMNSHO.

It sounds like you might have a light enough load, in total, to only need the 9kW generator. As pothers have mentioned, do a residential load calculation to find out. Here's a template I like to use for that: Residential Load Calculations - Mike Holt Enterprises.
 
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