- 66 Block Primary or Secondary 235V Surge Protector - UL Primary and Secondary listed with 350mA fuse for voice/fax/modem line (235V) - Dual Indicator Lights: Protection OK and Ground Connection OK - Solid-State Protection - Single Pair Protection: Protect only the lines requiring protection - Ideal for Retrofit Applications: Just remove the bridging clips from the block and replace them with the Protector, add the ground connection, and the pair is connected - Grounding Requirements: Field-installed solid copper wire - Recommended Grounding Impedance: