Xref: utzoo comp.misc:2776 sci.electronics:3266 Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!killer!ames!mailrus!rutgers!rochester!pt.cs.cmu.edu!sei!sei.cmu.edu!rsd From: rsd@sei.cmu.edu (Richard S D'Ippolito) Newsgroups: comp.misc,sci.electronics Subject: Lightning rods. Was: Protecting computer equipment Message-ID: <6179@aw.sei.cmu.edu> Date: 11 Jul 88 14:45:49 GMT References: <1988Jul8.045005.17867@utzoo.uucp> Sender: netnews@sei.cmu.edu Reply-To: rsd@ae.sei.cmu.edu.UUCP (Rich D'Ippolito) Organization: Carnegie-Mellon University, SEI, Pgh, Pa Lines: 27 In article <1988Jul8.045005.17867@utzoo.uucp> Henry Spencer writes: > [...] Lightning rods and the like are based on giving >it a more attractive place to go, not on stopping it from doing what it >wants. Ligthning rods work by _preventing_ the buildup of static charges in the vicinity of the pointed end(*). This reduces the formation of streamers radiating from the ground, which become the return path for the cloud-to-ground bolt when they reach the charged cloud. They do _not_ attract the bolt (God forbid!). Look at the size of that skinny pole and wire and imagine hundreds of thousands of amperes flowing through it... The normal path to the computer equipment is the same as it is for all other appliances -- through the power lines (and phone lines for a MODEM). Those utilities strive mightily to protect their investments with voltage-limiting sparkgaps and suppressors, but the resulting surges can still do in an electronic appliance. In many cases, an extra fifty-cents of protection is worth just about that, so it isn't worth the bother. I suggest commercial surge protectors on the lines, not in the equipment. Rich * Electric field theory will explain the reason for the sharp point.