The mains supply is provided via MCBs to both the bypass and UPS. In the normal state the UPS is protecting the load and R1 is energised. If the output of the UPS fails for any reason R1 will drop out and operate the mechanically interlocked contactors C1 + C2. If either fuse blows or R1 fails the system will drop out to bypass because the rest state of C1 + C2 is `on bypass'.
Of course the UPS will buffer the load from breaks in the input supply.
There will be a small break in the transfer but the system is extremely robust and uses readily available components.
The four neons a b c d indicate status.
If you would like a bespoke unit making up for a particular applcation - let us know so we can quote you.
A unit suitable for 30Amp single phase is about 12" cube.
