Uninterrupted power switch for 240V
To switch between two sources a single contactor with changeover contacts would normally be used. However, doing this with a mains AC supply is not recommended. Since there is (most likely) no synchronisation between the two supplies you could end up switching while one supply was at maximum positive peak voltage and the other at peak negative voltage. This would generally be considered a bad thing.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. A possible solution.


SW1 is the control.
With SW1 up RLY2 is energised and the circuit is powered by mains.
When SW2 is switched down. RLY2 is switched off. When it drops out RLY1 coil is energised and RLY1 is energised and the generator powers the load. Whether or not the resultant time delay is adequate is up to you to determine.
Switch back is a similar sequence.
The RF generator suffers a brief interruption in power during the transfer.
A small UPS powers the controller during the transfer and prevents the controller reset.