The FXN520 conventional standard base has been  specifically designed to be compatible with the Eaton  range of conventional detectors. 
 
This standard base has been designed for flexibility,  simplicity and speed of installation. 
It incorporates purpose designed devices to provide fault  warning if detector is removed whilst maintaining full  zone wiring integrity. 
 
The base has a schottky diode in series with the negative  terminals to enable fault monitoring and allow the circuit to continue if a detector is removed