Working on an ATS

[bpk]

We have an Onan automatic transfer switch that does not assume load when an outage occurs. I have done some basic troubleshooting and found an automatically resetable breaker that stays open all the time for the operation of the motor. My question for you guys is I have never done any work on transfer switches besides installing them, is this something that is a specialty or something that an average person (electrician) can tackle. We have some prints and manuals for it that look fairly easy to follow. It is an Onan model OTCU 260 amp 208 volt manufactured in 1989. Thanks in advance

 

[brian john]

Depends on you skill sets and ability with mechanical intution.

There is a CB on the linerar actuator?

Does the ATS have electronic or analog controls?

What you describe usually is a voltage frequency sensing on the generator portion of the controls.

Analog you can isolate and repair, electronic you buy a new card.

 

[qcroanoke]

Depends on you skill sets and ability with mechanical intution.

There is a CB on the linerar actuator?

Does the ATS have electronic or analog controls?

What you describe usually is a voltage frequency sensing on the generator portion of the controls.

Analog you can isolate and repair, electronic you buy a new card.

If it is the kind I used to work with they are electronic cards in them. Seems like there were 3 cards and 2 of them were the same card. we used to interchange them to see in the problem went to the other side of the switch so we would know if it was a card or not.
Does the actuator jump like it wants to go to the generator? Sometimes the actuator will get in a bind and try to transfer but it can't. If it is doing that disable the actuator and take the transfer mechanism back and forth a few times to see if you can get it back in sync.
I'll ask the obvious now. What is the voltage and frequrency of the generator? Is it within tolerance of what the ATS is looking for? If not the ATS will not transfer to it.

 

[bpk]

It has 3 electronic cards. When the last outage occured the generator started but never transfered load. One of the cards has an LED for emergency power available that was on, but it looked liked it never even tried to move the actuator (probally because of the in line breaker open). The actuator has a square rod thru it that makes 4 limit switches on the side when it is in the normal power position, and testing it with a meter one limit failed to close (the screws that hold the switch are loose). So Im thinking that the actuator kept trying to move to the normal power supply until all 4 limits were made but never made it and then the breaker finally wouldnt reset anymore. I checked the voltage output of the generator 120/208 and everything was right on. I have never actually dug into a transfer switch before so any info is greatly appreciated.

 

[brian john]

Silver faced cards that plug in or black and/or green cards that are bolted to the back plate.

 

[mxslick]

It has 3 electronic cards. When the last outage occured the generator started but never transfered load. One of the cards has an LED for emergency power available that was on, but it looked liked it never even tried to move the actuator (probally because of the in line breaker open). The actuator has a square rod thru it that makes 4 limit switches on the side when it is in the normal power position, and testing it with a meter one limit failed to close (the screws that hold the switch are loose). So Im thinking that the actuator kept trying to move to the normal power supply until all 4 limits were made but never made it and then the breaker finally wouldnt reset anymore. I checked the voltage output of the generator 120/208 and everything was right on. I have never actually dug into a transfer switch before so any info is greatly appreciated.

See highlighted part in the quote.

I feel you now have two issues:

A burned-out actuator and a bad breaker that has failed because it tried to reset too many times into that bad actuator.

Replace both to be safe.

 

[brian john]

The clearing contacts can come out of adjustment and not allow power to the actuator.

WITH THE ATS OFF?DEAD?NO POWER you have to check the clearing contacts.

As you manually operate the actuator one set opens prior to the other set closing.

If the contacts are out of adjustment the ATS may not transfer OR can machine gun and fry the linear motor.

Checking the motor is simple enough.

Check/test the motor

Check the clearing contacts and this is better completed by someone familiar with the ATS.

 

[bpk]

I believe the clearing contacts you are referring to are the limits on the side that had come loose and had not closed on the last transfer back to normal power. I fixed those and replaced the resetable breaker and tried it on a 3 phase 15amp circuit that I ran just temporary to simulate utility power( it has no load connected to it). It transfered fine now but upon retransfer when utility supply is restored it tried to actuate back to utility supply but the motor only moved the actuator about 3/4 of the way,like it didnt have enough power. The actuator moves nicely by hand. I immediatly shut it off to not cause more damage, but I'm thinking the motor should be replaced.

 

[ATSman]

Careful using temp power

Careful using temp power

I believe the clearing contacts you are referring to are the limits on the side that had come loose and had not closed on the last transfer back to normal power. I fixed those and replaced the resetable breaker and tried it on a 3 phase 15amp circuit that I ran just temporary to simulate utility power( it has no load connected to it). It transfered fine now but upon retransfer when utility supply is restored it tried to actuate back to utility supply but the motor only moved the actuator about 3/4 of the way,like it didnt have enough power. The actuator moves nicely by hand. I immediatly shut it off to not cause more damage, but I'm thinking the motor should be replaced.

It might be that your temp power source is not "stiff enough" meaning that the source voltage drops down when the motor operates preventing the force necessary to complete the transfer. I ran into this problem at a switchgear manufacturing plant. The KVA rating of the stepup transformer in their temp power test set was not large enough for the bigger ATS's they were bench testing.
I recommend testing it with the normal utility source and generator.

 

[brian john]

I believe the clearing contacts you are referring to are the limits on the side that had come loose and had not closed on the last transfer back to normal power. I fixed those and replaced the resetable breaker and tried it on a 3 phase 15amp circuit that I ran just temporary to simulate utility power( it has no load connected to it). It transfered fine now but upon retransfer when utility supply is restored it tried to actuate back to utility supply but the motor only moved the actuator about 3/4 of the way,like it didnt have enough power. The actuator moves nicely by hand. I immediatly shut it off to not cause more damage, but I'm thinking the motor should be replaced.

You fixed them DID YOU ADJUST THEM PROPERLY, out of adjustment clearing conntacts can pose several problems as noted.



Sounds like the contacts may be out of adjustment.

 

[bpk]

I made sure that when the switch is to utility power the 4 limits on that side are made and the 4 limits for emergency are open, and vice versa. Is there more to it than just that? Thanks for all your help, I appreciate it.

 

[brian john]

I made sure that when the switch is to utility power the 4 limits on that side are made and the 4 limits for emergency are open, and vice versa. Is there more to it than just that? Thanks for all your help, I appreciate it.

Yes it is the point where they open and close, open to soon and the switch does not have enough force to continue the transfer, open to late and they can drive the switch back and forth.