Safety apparatus for detecting an abnormality of power control element

Claim 1

A safety apparatus in a circuit for controlling an alternating current flowing in a load responsive to a control signal, said safety apparatus comprising: a power control element for controlling a supply of the alternating current to the load; control signal input means for inputting the control signal to control said power control element; first detecting means for detecting an operating condition of said power control element, said operating condition being one of the group consisting of ON and OFF conditions; second detecting means for detecting whether the control signal has been input to said control signal input means, wherein said second detecting means includes self-hold means for setting a self-holding condition if the control signal has been input and resetting said self-holding condition of said self-hold circuit in synchronization with the alternating current supplied to the load; third detecting means for detecting an abnormality of said power control element if said first detecting means is detecting said ON condition and said self-holding condition of said second detecting means is reset; fourth detecting means for detecting and forming an output if said third detecting means detects said abnormality over a time period of a half cycle of the alternating current; and cutting means for cutting off the alternating current to the load in response to the output of said fourth detecting means, wherein said cutting means includes a fuse and a switch, said fuse being arranged to be blown in response to the output from said fourth detecting means, and said switch being arranged to cut the alternating current to the load in response to said fuse being blown.