In normal operation, power is supplied to the bus via incoming line 1, with 1DL at close state and 2DL at trip state, and incoming line 2 as standby power supply for incoming line 1. In case of loss of incoming line 1 power supply due to fault etc., WBKQ01C device can be quickly activated to switch on incoming line 2 power supply. After clearing of the fault in incoming line 1, manual mode can be used to activate WBKQ01C device to switch the power supply back to incoming line 1.