ATS Won't Transfer back to Utility

Automatic/Manual transfer switch repair, wiring & troubleshooting questions
FarFromStock
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Sat Jan 12, 2019 1:35 pm

I have a 25kW Generac Guardian generator with a Generac 200A (model 0049451) ATS. When utility power is lost, the generator starts normally and the ATS transfers load to generator as designed. However, when utility power is returned, the generator turns off as normal, but the ATS does not transfer load back to utility. I have to manually transfer from generator to utility. Any suggestions on how to troubleshoot this issue?
Chris
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Sat Jan 12, 2019 3:13 pm

There's really only a couple of possibilities here.

First being that if for some reason the #23 wire which tell's the transfer switch to transfer is grounded along the way, or the relay inside the generator is stuck in standby mode. You would be able to tell this by starting the generator in 'Manual' mode. If the switch instantly tries to transfer to standby you have a grounded 23 wire. It would also try to transfer when the unit exercised (which it should not do).

If the 23 wire is normal and un-grounded when it's supposed to be, then I would check to see if you have a loose wire in the transfer switch to the upper coil. The 2 coils in the switch rely on 240V power from either the utility source or generator source. The upper coil gets power from the utility, broken through the small ice cube relay inside the switch and then through a small limit switch right next to the coil. If either the coil, wiring, ice cube relay, or limit switch are faulty, you will have this scenario.

All of the things mentioned above can pretty easily be checked with a quality digital volt meter. The 23 wire and 194 wires will be 12V DC voltage, everything else will be 120/240V AC voltage.
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78buckshot
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Sun Jan 13, 2019 5:38 am

I agree with Chris on diagnostics, there is no logic in the transfer switch itself so pretty simple to trace wires and voltage. The most common issue I have seen is one of the wires on the top(utility) solenoid is disconnected. If all wiring is in place then it's time to get your VOM out and check out the limit switch and transfer relay(ice cube).
danbike
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Wed Apr 24, 2019 9:45 am

We have a similar situation, but on an intermittent basis. Once I get it back to normal, it will switch correctly for a number of months. Any idea what could cause this intermittent issue?

Thank
Chris
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Wed Apr 24, 2019 9:52 am

danbike wrote:
Wed Apr 24, 2019 9:45 am
We have a similar situation, but on an intermittent basis. Once I get it back to normal, it will switch correctly for a number of months. Any idea what could cause this intermittent issue?

Thank
You need a small but of troubleshooting to determine if it's the switch, the generator, or a wiring problem.

When it won't switch back, you need to determine if the 23 terminal is grounded in the transfer switch. A meter set to measure DC will read 12V (or close to it) across 194 and 23 if the generator is calling for the switch to stay in standby mode. If you DO get 12V there and the generator is off, you either have a ground fault in the 23 wire somewhere, or the controller is stuck in standby mode for the 23 wire.
Generac tech for over 12 years. I'm here to help!
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DavidC
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Wed May 29, 2019 9:05 pm

I have a failure to transfer back to utility also. I have 7 Vdc across 194 and 23 with the generator off. Is that grounded? Battery voltage is normal, about 12.8 Vdc. I temporarily replaced the 23 wire between the switch and generator with no change in voltage. My generator does tie in manual and in test.
Chris
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Wed May 29, 2019 9:09 pm

7V seems like it might be enough to hold a 12V relay in.

When it won't transfer, have you tried removing the 23 wire at either end and see if it flips? Use caution doing this, since transferring under load with the cover off requires the proper PPE!
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
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DavidC
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Sat Jun 01, 2019 9:04 pm

I disconnected wire 23 at the generator and it did not transfer back to Utility.
Chris
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Sat Jun 01, 2019 9:56 pm

Then you have an issue in the transfer switch. Time to find out if you have a bad transfer relay, bad coil, or limit switch....
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
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dale@dmielectric.com
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Thu Jun 27, 2019 2:12 pm

I have a similar problem; When the utility power goes off the generator starts just like it should, but doesn’t transfer over. When I manually transfer it to the generator it will run till the utility power comes back on and then transfers back to the utility run for about 2 minutes the shutdown. It is not transferring to the generator.

Dale Haldeman
DMI Electric
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