Automatic Power Control Magnets are used to instruct an electric locomotive to open the circuit breaker on its transformer, so it does not draw current as the pantograph traverses a neutral section, to eliminate arcing.
A second magnet tells it to switch back on again afterwards. It is mounted on the end of a sleeper to align with the trainborne sensor. Using a simple spacer, the magnetic properties can be checked with either a standard Strength & Polarity meter or a Gauss meter.
