Mechanical Interlock
It is an accessory fitted between two contactors that physically prevents one from pulling in while the other is engaged. Its difference from electrical interlocking is that it keeps working even if an auxiliary contact welds or the wiring is faulty; for this reason it counts as a second and independent safety layer in forward-reverse installations.
The accessory takes the form of a latch or slide that sits between the moving parts of two contactors. When the core of one contactor moves, the latch blocks the path of the other; even if the second coil is energised, the core cannot seat and the power contacts do not close.
Why electrical interlocking alone is not enough:
- An auxiliary contact can weld; in that case the interlock logic is silently disabled.
- A wiring error made during commissioning can bridge the interlock path.
- A fault on the control side (two command sources operating in parallel) appears before the electrical layer.
When selecting a mechanical interlock, use the manufacturer's own accessory that matches the contactor series; forcing it onto contactors of a different size damages both the interlock and the contactor. After mounting, always test the interlock with no load: press one contactor by hand and confirm the other cannot pull in.
This layer is especially valuable in radio remote controlled installations, because the source of the command cannot be observed visually in the field; the fault has to be stopped physically.
The context in which this term is used: Wireless remote control installation: pairing, relays, safety