I have a few networked devices that don’t like being turn off and they really don’t like the power to them fail. I have multiple UPS units that supply power to these devices, but occasionally I need to do maintenance on the UPS. In those cases, I’ve had to turn everything off to change the power source. One solution that I came up with is a 110V relay that switches the power fast enough the device doesn’t notice.
The coil is attached to the redundant wire such that when it is powered the relay switches to it to support the equipment/load. That way the “Normal” connection can be removed from power without losing power to the critical devices.
I should mention that there are some irregularities.
1. The case shown can be opened which can expose dangerous voltages.
2. The design will falter if the alternate power cannot support the load.
(The relay will chatter, switching rapidly between the two sources.)
3. The design is not intended for switching inductive loads under power.
(Especially if the two sources are out of phase with each other.)
Of course someone came out with one that is actually cheaper than making one. LOL
