Abstract: A system for reducing the voltage of an AC electrical supply to a load for the purpose of energy efficiency, comprising a transformer and power converter in circuit between an AC electrical supply and a load, and a bypass switch S to cause the transformer to be taken out of circuit and to connect the electrical supply to the load in the event of a sustained overload of the transformer. The system includes means (14) to measure the temperature of the transformer, means (17) to measure the electrical current in the circuit and control means (15) receiving signals from the sensors (14, 17) and to operate bypass switch S to bypass the transformer and allow it to cool. A fuse F2 and thermal cut out device (16) are in circuit with the secondary winding of the transformer as failsafe means to interrupt the supply to the transformer in the event that the bypass switch fails to operate.