Electrical Interlock
A cross-wiring arrangement that prevents the forward and reverse contactors from pulling in at the same time. The normally closed auxiliary contact of each contactor is placed in series in the coil path of the opposing contactor; when one pulls in, the supply path of the other is cut. It is the basic measure that prevents a phase-to-phase short circuit in three-phase reversing installations.
In a reversing connection the forward and reverse contactors give direction by swapping two phases of the motor. If both pull in at the same time these two phases are bridged directly to each other and a short circuit occurs; the result is a blown fuse, a destroyed contactor or an arc injury.
The interlock is wired crosswise:
- The NC auxiliary contact of the forward contactor in series in the path of the reverse coil.
- The NC auxiliary contact of the reverse contactor in series in the path of the forward coil.
On a radio remote control this measure is even more critical, because there can be more than one source of commands: if the existing wired push-button installation and the receiver's relay output work in parallel, two different people can give opposing directions at the same time. A barrier at software or contact level on the remote control side is not considered sufficient on its own in this scenario.
Use the electrical interlock together with a mechanical interlock: if the auxiliary contact welds, the electrical layer is out of action, while the mechanical lock continues to physically prevent pull-in. During commissioning, test the interlock without load by triggering both directions at once.
The context in which this term is used: Wireless remote control installation: pairing, relay, safety