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Old 06-23-2019, 08:04 PM   #1
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Default Generator Utility Power Loss Sensing

Hello Guys,

Currently a customer has an Generac ATS and a C9 generator installed on their property and are using the ATS as a manual switch. However, they would like to have it automatically transfer in the event of a power outage.

The C9 has two contacts that will start the generator when they are shorted, and the Generac ATS will transfer load when a transfer contact is tied to low voltage ground and power is available on the generator-supply lugs.

So, obviously that can be achieved using magnetic contractors.

My initial thought was to use a 240v coil NC and a 120v coil NC coil on the line side of the transfer switch, where the control wiring would be wired in series (so if they lost a phase or neutral one of the contractors would pull out, closing two contacts that would short the start contacts of the generator and tie the transfer contact to ground).

My main issue with this plan is if the neutral is completely out, will the contractor chatter? Does any one have some experience with this?

I know the obvious solution is to get a cat Transfer switch, but its a 400 amp transfer switch and it would be a real pain to replace it, if an appropriate contactor arrangement would work just fine.

Last edited by MikesElec; 06-23-2019 at 08:11 PM.
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Old 06-23-2019, 08:41 PM   #2
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Disconnect the switch and the generator and take it to the local dump and replace it with a Kohler.
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Old 06-24-2019, 12:00 AM   #3
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You could just put 3 contactors in parallel (L1-N, L2-N, L1-L2) so if one or all of them trips it would start then generator.
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Old 06-24-2019, 12:03 AM   #4
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I think every one of the few single phase transfer switches I've worked with use only L1 and L2 for utility voltage sensing. The neutral is not involved.

If you're building your own system, I'd use time delay relays. Set the loss of utility at 3 seconds or so and the re-transfer back to utility at a few minutes.

If the transfer switch doesn't have a voltage-frequency relay on the gen side, I would install one.
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Old 06-24-2019, 06:52 AM   #5
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If its a standard Generac residential type transfer switch that has no intelligence built in, in other words meant to be driven by the Generac controller, you could try this:

https://pspproducts.wpengine.com/?p=1063

I didn't look to see whether this also has a weekly exercise function or not, though that can be done with a timeclock across the start contacts, like many older transfer switches have.
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Old 06-24-2019, 11:15 AM   #6
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Quote:
Originally Posted by samgregger View Post
You could just put 3 contactors in parallel (L1-N, L2-N, L1-L2) so if one or all of them trips it would start then generator.
Why use contactors when there are many adjustable V/Hz sensing relays specifically made for the application?
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Old 06-24-2019, 09:22 PM   #7
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Quote:
Originally Posted by micromind View Post
I think every one of the few single phase transfer switches I've worked with use only L1 and L2 for utility voltage sensing. The neutral is not involved.

If you're building your own system, I'd use time delay relays. Set the loss of utility at 3 seconds or so and the re-transfer back to utility at a few minutes.

If the transfer switch doesn't have a voltage-frequency relay on the gen side, I would install one.
Very common but just give you a head up and other readers as well.,,

If you run into 208 volt network make sure you are aware of the voltage sensing device can work with 200 volt setting cuz some will only go down about 210 or so before it drop out.
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Old 06-24-2019, 10:23 PM   #8
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Quote:
Originally Posted by nrp3 View Post
If its a standard Generac residential type transfer switch that has no intelligence built in, in other words meant to be driven by the Generac controller, you could try this:


I didn't look to see whether this also has a weekly exercise function or not, though that can be done with a timeclock across the start contacts, like many older transfer switches have.
This solution seems perfect. I purchased two of them. Thanks. The generator has its own exercise function...

Had to edit out the url due to post restrictions.
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Old 06-25-2019, 06:21 AM   #9
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They have some unique stuff. I have used some of their load shedding gear, but haven't tried that particular product yet. Let us know how it works out.
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