Force limitation
Force limitation is the requirement under BS EN 12453 that a power-operated garage door detect resistance from an obstruction and stop or reverse rather than continuing to close with excessive force.
It is typically implemented through the operator's motor current sensing combined with photocells. If a UK electric door reverses unexpectedly, it is usually the force-limitation and photocell system working correctly, most often triggered by a sensor fault rather than a genuine obstruction.