Mechanical and electrical interlock

A pure mechanical interlock will only have moving parts between the switches so it is impossible to have them set in a dangerous position - in this case presumably you cannot set the generator and the mains on at the same time. An electro-mechanical  interlock achieves the same end but at some point has wires and a solenoid or similar so an electrical signal from one switch is jamming or un-jamming  the other. The electrical bit allows things to be further apart and gives greater freedom of orientation etc. However it does need an additional power supply and what happens if that supply fails needs to be carefully considered to fail-safe.

If you have more detail of the set-up it may be possible to be a bit less fuzzy.

Mike