We have been having lightning problems at a customer site. The customer wants us to install a new grounding system. I am trying to figure out which protector I need for the extension ports. Below is an example of what I am looking for. I need to know what clamping voltage is required for the ports and
the proper fuse rating.

ITW Linx

You can use the 39's, but you will probably be better off using the 75.

I have, in the past spoken with nortel about this issue and i believe there are no fuse's made that will protect a norstar set.The set operates at about 25 v dc and was told anything more than operating voltage will blow the set.There was a jack"rj11" that had a built in fuse that was the only thing that was supposed to work "was recomended 1 station side 1 switch side".
Also only time i ever experenced a lightning hit was with off premise phones "3 building site"never blew 75 volt fuse but toasted phones.Also when push came to shove off premise sets were not supported by nortel.

we had a bunch of multi extension fused protectors at our old site for our 8x24, we had a tie cable that liked getting hit by lightning. if i can get to the old site i will see if there are any left to get you a name, 14 of the 16 buildings over on the campus are gone, so im not too sure

I have had very good luck with ITW-LINX UP2B-39 on both ends. To check your protection ground, take a loop current reading, then move your clip from the grd. side of the line to the protection grd. it should read 30% or better, less than that tells you have a poor protection grd. Also check all grds. available, The reference should be 3 ohms or less. This checks the Multi- Neutral.