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Asco Transfer switch Troubleshooting - PartsAPS

asco transfer switch troubleshooting

ASCO offers low & medium-voltage generator transfer switches in automatic and manual models. These transfer switches reliably transfer electrical loads between normal and emergency power sources as well in critical power systems. However, ASCO transfer switches will get damages. You can troubleshoot the basic issues simply to avoid severe damage. From this blog, you can know the cause and solution for your ASCO transfer switch problems.

ASCO Transfer Switch Troubleshooting

This ASCO transfer switch troubleshooting guide describes some of the simple causes of problems with the installation of an automatic transfer switch.

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Utility acceptable light does not come on when utility power is connected to the transfer switch

  • Check that the utility feed is connected and its circuit breaker is ON.
  • With all power off, you have to verify that the utility feed is 220 to 240 volts AC and 60 Hz. Also, check the voltage and frequency settings.
  • Check that the utility feed is wired to the terminal lugs on the bottom of the transfer switch marked L1 and L5.
  • Finally, you need to inspect whether the transfer switch harness is connected properly to the controller or not.

Generator does not crank when the utility source fails or when the transfer test button is pressed

  • Press and hold the transfer test button for at least 15 seconds.
  • Check that the generator starting controls are set for automatic operation.
  • You have to verify that the generator battery is connected and check whether the battery voltage reaches the recommended voltage.
  • See for the correct contact, i.e., normally open or closed is being utilized.
  • Turn off the power and verify that the engine starts low voltage wiring between the generator and controller terminal block. See if the plug is placed properly in the receptacle on the controller.

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Generator cranks but does not start and run when the utility source fails or transfer test button is pressed

  • You should verify whether the generator operation is going correctly or not. Check fuel in the tank, oil level, spark plugs, etc. as per the specifications given in the ASCO transfer switch manual.
  • Check the engine start low voltage wiring and see for the plug is seated properly or not.

Generator starts and runs but the transfer switch does not transfer the load to the generator

For this problem, first, you have to verify that the generator's acceptable light is ON. If that light is off, you need to go through the previous issue troubleshooting process. You must remember that an automatic transfer switch won't transfer the load to an unacceptable source. In addition, check that the ATS harness is connected properly to the controller.

Transfer switch does not transfer the load to the generator immediately

  • You will need to verify that the generator's acceptable light is on.
  • Wait for 10 seconds for the transfer to generator time delay. This fixed delay allows the generator output to stabilize before a load is applied to it.
  • Now, press the bypass time delay button for immediate load transfer to the generator.

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ATS transfers the load to the generator but the generator slows down

Because of generator overload, you may get this issue. So, check to see if the circuit breaker is tripped. Be sure the load doesn't exceed the capacity of the generator. Some motor loads require three times more power to start.

Check for the short circuit in a connected load. Moreover, you have to observe the load on utility and general lights as well.

Generator stops after running for a while

If your generator stops working after running sometimes or an automatic transfer switch retransfers back to the utility, it may have run out of fuel or shut down because of low oil level. So, check and fill the tank. In addition, you need to check for generator overload and short circuits in the connected load.

Transfer switch does not retransfer the load back to the utility

  • Check that the utility acceptable light is on as ATS will not transfer the load to an unacceptable source.
  • You have to wait for five minutes for retransferring to the utility time delay. The utility should be acceptable for 5 minutes continuously.
  • You can press the bypass time delay button to transfer the load to the utility immediately.

ATS retransfers the load back to the utility but the generator keeps running

  • If the generator continuously running even the transfer switch retransfers the load back to the utility, wait for two minutes for engine cool down/ unloaded running time delay.
  • The engine cool down fixed time delay is important to prevent generator damage.


How often should automatic transfer switches be tested?

You should test your automatic transfer switch for every 30 days. You need to perform testing of transfer switch and generator set under load and operating temperature conditions. A 30 minute exercise period is an absolute minimum or the engine manufacturer's recommendations should be followed.

How does a closed transition transfer switch work?

A closed transition transfer switch creates a connection to the new power source before breaking its connection to the old one. As there is no gasp between disconnection and connection, downstream loads will receive power throughout the transfer process.

How do you check if your generator is working?

You have to measure the voltage across the battery and it should be about 12.6 volts with the engine off. The voltage should be increased to somewhere around 14 volts when the engine speeds up. If it does, consider that your generator is working and charging the battery.


I hope this article was helpful. If you need further assistance, you can refer to the manual or contact a technician. If there is any need to replace parts, do it immediately. You can get ASCO replacement parts from here online. We are very happy to help troubleshoot your ASCO transfer switch and have in-stock ASCO parts to get you back up and running.

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