The ancient Romans could have made one. It has no moving parts, no connections that open and close sputtering arcs of metal vapor as do relays, and no semiconductors to fail when their part per billion impurities finally migrate far enough to cause a short or reduce gain. To turn on the load, put a relatively weak DC current through the controlling coil. The larger number of turns in the input coil allows a small current through it to overcome any demagnetizing forces produced by the load current flowing through the output coil. MCAs can also exert proportional control over the power to a load.
Bridge circuits enable bidirectional control.
Individual MCAs in a control system may be very reliable, but that does not mean the system will fail safe if one of the MCAs fails. If it freezes while it is reaching inside a car body going by on a conveyor belt, the car body will collide with the arm. Look at the whole system. Report problems with the web pages to the maintainer .