What is the meaning of wiring style class a?

Answer 1

In the field of fire alarm wiring (and possibly others) the wiring going out to the devices in the field can be wired in several ways depending on the need for survivability. Older codes/manufacturers created a concept known as CLASS-A and CLASS-B CLASS-A is a 4 wire circuit where two wires of the circuit leave the control panel, make connection with the field devices, and then return to the same control panel. In this type installation a wire that broke or came loose would cause a TROUBLE condition but all devices would continue to be available to detect an alarm. CLASS-B is a 2 wire circuit where two wires leave the control panel, make connection to the field devices and then connect to an "END-OF-LINE" device. Each CLASS-B circuit is a "deadend". If a wire broke or came loose a trouble signal would occur, but all devices downstream of the break point would not function. ---- As technology enhanced, newer systems were able to provide more capabilities than just the two described above. The NFPA 72 Fire Alarm Standard created a system that describes the ability of each type circuit. This system describes the types of circuits as "STYLES". It also uses letters but uses the other end of the alphabet, such as Style Y, Style W, Style X