The CSFI is designed for mounting in distribution boards to provide secondary protection against power surges caused by external sources such as lightning strikes & substation switching as well as providing a measure of protection from surge events generated on the secondary side of the filter. An ideal device for Category B locations. The CSFI is a 3-stage protection unit utilizing primary & secondary MOV protection in conjunction with a low-Q LC filter. All CSFI units are provided with indicators showing power & protection status. Alarms are indicated on the front panel of the unit. The alarm function provides a summary alarm output for protection degradation as well as power failure. The protection alarm is configured to partial protection failure.