When I remodeled my house about 3 years ago, an electrical upgrade was done that included replacing all non-temperature rated wiring (cloth wrapped, without ground wires) and adding a pre-wired automatic transfer switch with service connection located on the side of the house. The ATS panel is rated 240v/50A and is connected to the main breaker panel via a double pole 50 amp breaker. It has several important circuits on it, including sump pump, refrigerator, freezer, gas burner equipped heat pump, boiler, strategic general lighting circuits, and alarm system. I have not gotten to the point to put in a permanently installed generator, but I do have a portable generator rated 7000 watts with L14-30 connector that matches the service connection to my house for the emergency generator, also a L14-30 connector.
I recently decided to test this setup and see how it works, so I could see if I am ready for an outage. So, I set the thermostats down on my heating systems and switched my heat pump to emergency heat so it would only run gas heat. Then, I connected up my generator to the house and started it up and let it run for a few minutes to warm up. Next, I threw the 50 amp double pole breaker in my main panel to kill utility power to the ATS. After the 20 second timeout, I heard the ATS pick up on generator power and the emergency circuits came back on. All seems as it should, so I moved on to the next test - filling up the sump pump crock to get the sump pump to kick in and empty out the crock. Before I get the sump crock filled with water, I heard the generator governor kick in and then smelled electrical burning, so I canceled the test and went back and restored utility power to the ATS by resetting the 50 amp breaker in the main panel and letting the generator run unloaded and disconnected to cool down. Found out that the transformers (120v-24v) in both the heat pump and the boiler had burned up and had to replace them. Never even got to do the sump pump test on the generator, but did complete it on utility power, just to make sure the sump pump still works. No other equipment has been identified as damaged in this test.
So, any thoughts to share on what might have happened that would have burned up those transformers? If there was a surge, wouldn't a circuit breaker on the generator or ATS trip? Would a brown out burn up a transformer? Is it likely that the generator can surge to that level of damage? Granted, the transformers are probably the most sensitive devices in this scenario.
How should I test this out, without destroying any more expensive parts or equipment?
Everything is fine now that I am back on normal power and after replacing the burned transformers.
Any thoughts would be appreciated, and having the system tested by a licensed electrician is also a fair recommendation, but I just want to make sure I have checked all the easy suspects.