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I am in the process of trying to finalize selection and installation of a standby generator for my house.

A couple of years ago, while the house was under construction, the electrical contractor on the project installed a Kohler brand automatic transfer switch. The model number of the switch is RDT-CFNC-0400ASE. It's a lot like the one here on Kohler's web site. The only difference is that on the inside of the front panel of mine, the "Material" number is "RDT-CFNC-400ASE -QS2", while the Kohler web site's product page shows the number ending is "-QS3". I'm assuming that that part of the number is just some sort of revision code, and that the switch is fundamentally identical.

While I had told the electrical contractor that we would be buying a Generac generator before they installed the switch, they told me after they'd installed the Kohler switch that it didn't matter, and that the Kohler switch would work fine with a Generac generator.

Now, the dealer I've talked to about the generator itself, who sells both Generac and Kohler products, has told me that the transfer switch manufactured by Kohler can work only with Kohler generators, and so now I'm stuck having to buy a Kohler generator instead of a Generac.

Is this correct? If so, is there any practical way to adapt the switch so it would work with Generac equipment?

I could of course get into an argument with the electrical contractor and make them rectify their error, but at this point it's going to be "he said, she said". That's a lot of headache for a very uncertain outcome.

I could also of course pay to have a different switch installed, but given that my only real reason for preferring Generac over Kohler is that their price/generated-kW is better, that extra work would more than consume whatever monetary savings I might have gotten by purchasing a Generac model.

So I'd like to know if there's some way to allow for a Generac option in a way that would be acceptable to all parties involved, but without involving some huge expense.

  • Do you have a part number for your existing switch? – brhans Sep 9 at 20:57
  • @brhans: sorry, I should have included that. I've added that information to the post. Thanks for the reminder! – Peter Duniho Sep 9 at 21:41
  • Are Generac and Kohler your only options here? Also, what kilowattage of a generator are we looking at here? – ThreePhaseEel Sep 10 at 0:21
  • @ThreePhaseEel: those are the only two brands that seem to be readily available in my area, for sales and service. If there are other reliable, cost-effective brands that would be worth looking at, happy to hear about them. Especially if they'd work with the Kohler automatic transfer switch. – Peter Duniho Sep 10 at 0:24
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    @wallyk: I'm north of you, Seattle area. Yes, I have had my share of bad experiences with contractors who ought to be able to provide good, expert advice but who instead just work as hard as they can to sell me the one thing they have any experience with, ignoring any aspect of what might actually work best for my scenario. – Peter Duniho Sep 10 at 0:57
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No, he is full of it. A transfer switch is just a switch. Kohler doesn't even make the switch they sell, neither does Generac. In fact the switch mechanism inside of them is the same (the electronics are different and they use different brands of circuit breakers). The only issue is that the wiring diagrams likely show you specific connection references for their own respective brands. But anyone with half a brain can figure that out.

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    This is a bit of an oversimplification: Generac and Briggs&Stratton use a setup where the actual transfer control is done by a board inside the genset (with 240VAC utility sense brought from the transfer switch), while Kohler and Cummins keep all the mains stuff in the transfer switch box, bringing only low voltage (roughly, generator start, although the resi Cummins switches don't have a full controller built in) wires over to the generator side – ThreePhaseEel Sep 10 at 0:20
  • @ThreePhaseEel: thanks for that clarification. Based on what you wrote, I infer that while the Kohler switch would work with most "dumb" generator setups, a Generac setup in particular would be problematic, unless there's a way to bypass the logic board in the genset and/or drive the transfer set from that logic. – Peter Duniho Sep 10 at 0:26
  • All that said, there are apparently prebuilt boxes for adapting Generac switches to work with other folks' generators (look for a PSP Products KGC-1) – ThreePhaseEel Sep 10 at 0:30
  • @ThreePhaseEel: okay, well...that would be great if I had a Generac switch and wanted to get a Kohler generator. But I'm in the opposite situation. I'd need a kit that would adapt the Kohler switch to work with the Generac generator (it presumably would either bypass the genset logic board and signal the start from the transfer switch, or it would bypass the switch's logic board and use the genset logic board to activate the transfer.) – Peter Duniho Sep 10 at 0:41
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    @PeterDuniho -- for your scenario (somebody else's transfer switch with a Generac generator), I have read some online instructions that say there are dealer procedures for setting up a Generac generator to use a conventional 12V, 2-wire start signal – ThreePhaseEel Sep 10 at 0:51

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