How to troubleshoot Transfer Switch
Low voltage is harmful to most appliances. Contactor-based transfer switches are also affected by low voltage; if the voltage level drops far enough the contactor points will “chatter”. Sustained contact chattering can cause transfer switch damage. Switches that have been damaged by chattering need to be returned to the factory for replacement.
General Low Voltage
Low voltage can be caused by low voltage conditions such as an RV park with inadequate wiring for crowded camper conditions where everyone’s electricity suffers (brownout). In this case a voltmeter will be helpful and will show a low voltage reading from the park receptacle, even before the RV is plugged in. When you experience general low voltage conditions, remember that brownouts can be harmful to most appliances. A better alternative might be to utilize a Solar System (or generator) until park voltage conditions improve.
Localized Low Voltage
Low voltage conditions can be caused by specific situations such as an additional cord, which is too long and too small for the load. Do not attempt to extend the RV power cord by using a 16-gauge 100-foot extension cord, or any cord not rated for an RV-size load. A localized low voltage condition will result when a load is turned on which is larger than that which the cord is designed for.
As soon as the RV tries to draw more current than the amount for which the cord is rated, the voltage will fall within the length of the cord, and the RV will experience low voltage. This is especially noticeable during in rush current situations such as an air conditioner start-up. This affects contactor-based transfer switches. The compressor will try to start; the voltage will drop, which will cause the contactor to drop out, at which point the voltage will rise to the pre-in rush level. The contacts will chatter when the A/C compressor kicks in, however the voltage may read normal.
Most meters are not fast enough to record this voltage drop. You can test for low voltage readings during this inrush cycle by reading voltage at the contactor terminals while manually holding the contactor plunger down in its closed position. This will override the chattering condition and the meter will have time to register the reduced voltage. If this condition exists, identify and correct the low voltage situation before proceeding further.
Some transfer switch models have wiring connections made by wire nuts on 6″ leads. Occasionally on these models, the wiring connections will get folded into the can in such a manner that the wiring will interfere with the physical operation of the relay. Visually inspect for free operation of the relay(s).
This may cause a humming coming from the coil on the transfer switch. Re-applying connections will sometimes help with this issue.