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Old 06-25-2010, 07:11 AM   #1
WMA
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Default ATS wiring

A customer is buying a 20 kw generator and 200 amp ATS from his propane company. It's Bryant (Generac...). The transfer switch does not include a service disconnect. Customer wants the transfer switch inside (service is in garage), to avoid another big gray box on the outside of his house. Would a meter socket with disconnect suffice as disconnecting means, or do I need to put a 200 a disconnect inside, in sight? Also, am I required to provide a disconnect for the generator power at the transfer switch? Any advice, dire warnings, etc. appreciated.

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Old 06-25-2010, 08:19 AM   #2
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Originally Posted by WMA View Post
A customer is buying a 20 kw generator and 200 amp ATS from his propane company. It's Bryant (Generac...). The transfer switch does not include a service disconnect. Customer wants the transfer switch inside (service is in garage), to avoid another big gray box on the outside of his house. Would a meter socket with disconnect suffice as disconnecting means, or do I need to put a 200 a disconnect inside, in sight? Also, am I required to provide a disconnect for the generator power at the transfer switch? Any advice, dire warnings, etc. appreciated.
It sounds like you are dealing with an existing 200 amp service and plan to interrupt it entirely. If so, you will need a service disconnect and your ATS will need to have load shed capabilty as that 20 kW will most likely not carry the entire residence.

A meter socket with disconnect will suffice.


Last edited by yucan2; 06-25-2010 at 08:21 AM.
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Old 06-25-2010, 08:46 AM   #3
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Actually, existing is a 100 amp service that's borderline adequate. Customer is planning to add a compressor and air handler. Does the requirement for load-shedding depend on the connected load or the service rating?
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Old 06-25-2010, 08:53 AM   #4
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The 200amp Generac ATS I'm familiar with is also rated as a service disconnect. Are you sure the one you are looking at is not?
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Old 06-25-2010, 09:00 AM   #5
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Distributer says it's KGATX0201200, without disconnect.
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Old 06-25-2010, 09:12 AM   #6
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Maybe you can check with another distributer, but I'm looking at a 20kw ATS now in a catalog and it is rated as a service disconnect. Sorry no model numbers. It is a Guardian by Generac. Sold at Home Depot.
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Old 06-25-2010, 09:14 AM   #7
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Actually, existing is a 100 amp service that's borderline adequate. Customer is planning to add a compressor and air handler. Does the requirement for load-shedding depend on the connected load or the service rating?
Yes. Load shedding is required when the generator that you are installing cannot safely carry the entire available load.

The way the load shedding works is thus: All critical loads are placed on the non-load shedding side of the ATS. Meaning that the generator can safely carry these critical loads within its rated capacity. All other loads are placed on the load shedding side.

If a predefined drop in hertz is detected, the ATS will drop all the non essential loads, that is to say all the loads on the load shedding side. This can be a permanent disconnection or be allowed to restart at a predetermined time up to a finite number of attempts.

The Generac RTSX200A3 is not service rated. The RTSD200A3 is. Depending on how you intend to install determines which one you need. Another option is the RTSS200A3, service rated ATS.

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Old 06-25-2010, 12:11 PM   #8
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Yes. Load shedding is required when the generator that you are installing cannot safely carry the entire available load.
OK, so it's connected load, not main breaker rating?

Gas company sold my guy a package. I'm stuck with the ATS without disconnect.

No disconnect required for the generator power, other than the one built into the generator?
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Old 06-25-2010, 12:21 PM   #9
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article 702 has all your answers (I just can't remember them)
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Old 06-25-2010, 12:23 PM   #10
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Yeah, the code book is out in the truck, but the world is right here. Caught being lazy...
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Old 06-25-2010, 01:24 PM   #11
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OK, so it's connected load, not main breaker rating?

Gas company sold my guy a package. I'm stuck with the ATS without disconnect.

No disconnect required for the generator power, other than the one built into the generator?
That is correct, unless of course the generator breaker were feeding a panel or some such with a lower unprotected rating than the generator breaker, for which obviously is not the case here.

If you're locked into that ATS, here's what I would do, especially since the customer doesn't want a "another large box outside".

Install a 2 pole 60 or 100, depending upon your needs, into the existing panel. Feed the ATS from there. Feed a new panel (MLO), from the ATS. Pull over all critical circuits up to the generator or your installed feeder breaker capacity, to the new panel. Obviously this is not a whole house solution, but a workable one and code compliant. However, if the ATS that he purchased does happen to have load shed capability and you utilize it as such, other but similar options should be implemented.

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Old 06-25-2010, 08:20 PM   #12
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That is correct, unless of course the generator breaker were feeding a panel or some such with a lower unprotected rating than the generator breaker, for which obviously is not the case here.

If you're locked into that ATS, here's what I would do, especially since the customer doesn't want a "another large box outside".

Install a 2 pole 60 or 100, depending upon your needs, into the existing panel. Feed the ATS from there. Feed a new panel (MLO), from the ATS. Pull over all critical circuits up to the generator or your installed feeder breaker capacity, to the new panel. Obviously this is not a whole house solution, but a workable one and code compliant. However, if the ATS that he purchased does happen to have load shed capability and you utilize it as such, other but similar options should be implemented.
That would be my advice as well.

Two panels, one normal power, the other emergency power.

Rob
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Old 06-25-2010, 10:33 PM   #13
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Like this

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Old 06-26-2010, 12:29 AM   #14
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Pretty much like that
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Old 06-26-2010, 12:13 PM   #15
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Sounds like a plan; thanks.
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Old 06-26-2010, 02:47 PM   #16
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In the picture, the 200 Amp MB panel on the left is original with the house. The enclosure on the right is a Kohler 100 amp ATS with built-in 12 circuit busbar. The ATS is protected by a double 60 amp circuit breaker and the generator is capable of supplying 18,000 watts. Hope this helps.


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