If the power is cut, does the remote control command stay latched?
It must not. When the supply is cut the receiver's relays drop out, the contactors release and the motion ends. So that the machine does not start by itself when power returns, a self-holding (sealing) circuit or a restart interlock with a phase protection relay must be built on the panel side.
There are two separate questions: what happens at the moment of the cut, and what happens when power returns?
At the moment of the cut the relay coils are left unenergised, the contacts open and the contactors drop out. On lifting machines the mechanical brake is also designed to grip when power is cut; the load stays suspended. IEC/EN 62745 explicitly addresses the behaviour on loss of supply in wireless control systems and expects a defined, safe outcome.
When power returns the real risk begins. If the control button is still held down, or if the circuit is built as a straight-through connection, the machine may start moving by itself; this is one of the most frequently overlooked hazards in the field. The countermeasure is standard:
- Build the direction contactors with a self-holding (sealing) circuit; when power goes the seal is broken, and when it returns the motion does not start until the operator gives a fresh command.
- On three-phase systems add a phase sequence and phase failure protection relay.
- Document the restart interlock in the circuit diagram.
On the ST100 and SF100 sets the ability of the manual button and the RF remote control to work in parallel makes a controlled restart easier when power returns. Confirm your set's loss-of-supply behaviour from the user manual.
The full topic: Wireless Crane Remote Control Selection Guide