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.