Prevention of Automatic Restart (Restart Inhibit)
It is the logic that prevents the machine from moving by itself when interrupted power returns or a fault clears. To restart, the operator must give a new and deliberate start command; the command is not held in memory and applied together with the power.
The hazard scenario is clear: the mains is interrupted, the operator thinks the machine has stopped and walks near the load, the power returns and the movement carries on from where it left off. What prevents this scenario is that the control logic does not treat the return of power as an automatic start signal.
In practice there are three common solutions:
- Self-holding circuit: the contactor is sealed in through its own auxiliary contact; when power is lost the seal breaks and it does not pull in when power returns.
- Momentary control logic: because movement continues only while the button is pressed, the old command is no longer valid when power returns.
- Undervoltage coil: the breaker trips when the voltage drops and does not close again unless reset by hand.
On radio remote control sets with relay outputs, momentary control logic provides this protection naturally; in applications using latching outputs, however, you must additionally build a self-holding circuit or undervoltage protection.
The context in which this term is used: Wireless Crane Remote Control Selection Guide