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Transfer Switch
Someone please check my logic on this troubleshooting. I went for a warm-up run saturday and when I plugged back into the shore power I had no power on the electrical breaker panel.
I have a contactor based transfer switch made by a now defunct company, no manual, no wiring diagram, no support. Comprised of 2 – 75Amp contactors with a relay to cut the shore power contactor coil voltage if the genny is running. Should the coil fail, the genny power contactor coil voltage is also cut off by a set of aux contracts which are opened when the shore power contactor is closed.
While I suspected the relay, it checks out fine. The auxillary contacts also open and close as they should. So the control system seems to check fine.
I put 120 volts on the shore power contactor coil and it closes as it should. 0.2 ohms across all three poles (2 hot and neutral) power lead contactos when closed and “O.L.” when open.
I put 120 volts on the genny contactor coil and it closes as it should 0.2 ohms across all three poles. BUT BUT BUT when the coil is de-energized and the power contacts are open as indicated by the “manual activation button” I still get 0.2 ohms (indicating a closed switch) across the neutral contactor, 150 ohms across one hot and 200 Mega ohms across the second hot. When I expected to see open circuit indications.
To me this indicated the contactor is bad (I have ordered a replacement). Both contactors are the same model and I would expect the same behavior.
Is there any reason why the neutral should not open? Or all three poles not showing open circuit when the contactor should be open. Is this how contactors fail? I don’t have any experience with these.
Since this is a heavy duty 75 amp switch I prefer to fix it rather than just replace it with a new 50 amp transfer switch.
Confirmation i’m on the right track here?
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4 Replies
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Fully agree. At the age of your coach and the likely number of cycles each has switched it might take a big chunk of the money you spend for dues, but I would replace the contactors and the associated relays. You do not want to go to a 50 amp box because on those instances when you want to load up the circuits on the genny you have the capacity.
I presume any time you connect or disconnect you are turning off all loads, but would still like to hear about any signs of arcing or stuck contactor points. Also, if over time the cable connections from shore or genny power have loosened if you see evidence of heat damage.
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For future reference Jon, if one replaces the transfer switch and the choices are 50 amp or 90 amp, your saying go with the 90 amp?
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Jon,
I try to switch power sources with no loads, but I also know it has happened a few times. Both when starting the genny and when plugging in.
i have two replacement relays and one contactor headed my way. This is a PIA as it on the ceiling of the front bay but, it sure beats trying to find a replacement without significant rework. I may get a second contactor and then the whole switch will be rebuilt. At least it happened in the barn and not at some campground.
i will try and open the failed contactor to examine the condition and will report back.
Thanks for the feedback.
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Dan, I think I understand your question, but to be sure there is no chance for misinterpretation regarding my opinion on this, the short answer is yes I would always opt for the greater capacity.
This point I want to make very clear because it is a safety issue. On my coach I have 70 amp circuit breakers relating to the transfer switch. If I replaced my transfer switch with a 90, the loads the contactors could handle would be 90, but I am protected because the wiring was sized for 70 and there is circuit protection for 70.
Increasing the size rating of components is perfectly fine as long as the circuit protection and wiring are sized for their capacity, which may be less.
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