[Cricketman]

Is there a type of load sensing transfer switch or relay switch that can power 2 devices from a single power source in such a way that one device acts as the main unit and the other a backup unit. In the event the main device fails, power transfers to the backup device?



Specifically, I'd like to install 2, 220v single phase air blowers for fish tanks. One would be the main unit and be normally on. The other would be the backup unit and would be normally off.


Assuming a load sensing switch exists, the one issue I've considered with using load sensing as a means of determining which pump operates is that a mechanical malfunction of the main pump might disable the pump, but not stop it from drawing a load, thus not switching over to the backup unit as intended.
An alternative to this might be to use the spinning motor of the main pump to power a low voltage relay. That way, if the motor stops spinning, the relay loses power.



Any advice would be much appreciated in terms of products designed specifically for an application like this or perhaps a family of switches or devices that would be a good starting point for further research.

[cdad]

Why not just hook them both up and use a standard pressure switch to control the second unit. Just T in from the main unit for the switch. If you know the pressure output of the pump then get a switch to match. Should it fail pressure will drop and the second pump (so long as correctly hooked up) will turn on.

If this is needed because your keeping expensive fish then also consider a UPS for your pumps in the event of a power failure.