Device for limiting standby power consumption

A standby power consumption limiting device is provided for connection between an electricity supply and an electrical appliance of the kind having a main on/off switch, two power supply input terminals and a standby mode control circuit operable, when the appliance is switched "on", to place the appliance in a reduced power standby mode. The device comprises a standby mode detection means 102 effective to detect and indicate that the appliance has gone into standby mode and a power switching means 104 having a first state in which the electricity supply is connected to the appliance via its power supply input terminals 91 and a second state in which the electricity supply is disconnected from the appliance. A power switch control means 107 responds to an indication from the standby mode detection means that the appliance has gone into standby mode, by switching the power switching means from its first state to its second state, thereby removing power from the appliance. At this point, a test signal generating means, 105 connected to one of the appliance input terminals by the power switching means when in its second state, generates a test signal of predetermined form, said test signal being returned, while the appliance main switch is in the "on" state, via the other appliance input terminal. A test signal detection means 106, connected to said other appliance input terminal by the power switching means when in its second state, is capable of detecting the test signal returned via said other terminal, when the appliance main switch is in its "on" state and of detecting a predetermined change in the returned test signal indicative of the appliance main switch having been turned to its "off' state. The power switch control means is responsive to an indication from the test signal detection means that the appliance main switch has turned been turned "off' to put the power switching means back into its first state thereby restoring power to the appliance which will then become active when its power switch is returned to the on position.