Hallo Mehdi,

first let me recall your scheme:



If you want to add lightning protection, then this must come first! Filters and other stuff can be added, but must be located behind lightning protection!
Also, adding fuses is nice. But they must be able to withstand the stresses they shall keep off the following parts. So, a polyfuse is not suited to protect the lightning protector, as only relatively low voltages may be applied to a polyfuse. You can add a polyfuse behind the lightning protector to handle shotcircuits of phone lines. Then, the lightning protector also protects the polyfuse...

I would recommend you the following circuit, which sits in standard lightning protectors also providing line filtering:



First comes the lightning protector, which isn't fused, by the way. Then come two 33µH chokes and a transzorb. These parts provide a fine protection, as the remaining overvoltage is furtherly clamped, to about 200V. As the transzorb shows a parasitic capacitance of about 350pF, in combination with the two chokes it provides a line filter (low pass filter) showing a corner frequency of about 1MHz.
You can add further capacitors and chokes to this circuit to form a T-filter. But then all parts must come behind the transzorb: Connect two 1nF/1.5kV capacitors (y-capacitors are idealy suited!) from each line to signal ground, and add tow more 30µH chokes running to your circuit. This T-filter will not only dampen interference from outerworld, but also to outerworld.

If fuses are needed to prevent trouble from destroyed lightning protector, then I would take two 1.25A glass body fuses, filled with sand, and locate them in front of lightning protector.

Kai