mrb@psueclb.BITNET (11/28/87)
Hi --
With all the recent postings about surge protection on power lines, it is
important to restate/emphasize one thing ---
Make sure you fuse (or otherwise overload protect) any circuits leading to
surge protective devices.....or, in other words, don't just hang 'em across
the power lines without a fuse in the way.
Now sure, the fuse can blow and you'll be left without that surge absorber
in service...that's why some people put indicators (neon lamps, etc.) across
the surge protector so you can tell when they are in circuit. Won't tell
you if the movistor is "worn out" --- just if it is across active lines.
When the fuse blows, the lamp goes out. Of course, you have to look at the
indicator every once in a while, but that's another story.
One particular episode convinced me of this...back in the mid-1970s, I worked
at a TV/FM station. We were always losing rectifier stacks, etc. with every
big thunderstorm that came our way. So the boss bought these mammoth
thyristor-type surge protectors in a big steel box, and hooked them (as
intended by the mfr.) across the incoming 480 V - 3 phase AC. No fuses, etc.
in the way. Well, comes the first big thunderstorm and BLAMMMMMO! One of the
devices couldn't hack a surge (maybe a direct hit, who knows?) but in any
event it failed and became a dead short. Blew the steel cover right off the
box!! Complete with smoke and sparks and all. Impressive!
So fuse those surge suppressors, even the little ones on distribution
circuits. It's cheap protection.
MRB @ PSUECL
dbaden@afit-ab.arpa (Doug L. Baden) (12/12/87)
[this line for the voracious mailer in you] I worked in a pager house (we rented and operated pagers) until a few years back (I got my progamming degree). As second engineer, I had the fun of cleaning up after lightning strikes. The worst problem I encountered was that breakers take time to release. Lots of time as far as lightning is concerned. So much in fact that the electronic components get fried. Completely. Guess what most of those power strips use for overload protection. Yep, circut breakers. A fuse will melt very fast to give you the best protection possible in a very bad situation. MOV's will not do it if they have been hit once with a good jolt. They can burn out too. Another thing, don't forget the CRT terminal too. Another little hint to all of you netlanders out there on modems, don't forget the telephone wires. The worst cleanup I ever did was when the phone lines got me. There are lightning arrestors for phone lines, but I really don't know how well they work. We made our own with phone company approved arrestors (much like neon bulbs) and two 500 millihenry cores in series with the line (one on each line). Lightning has a high frequency and just HATES this. So it will take the easier path, the lightning arrestor. This worked. Cut the line level though... But after all is said and done the best lightning protection is this: Unplug it. This always works. The rest of the protection is only for when you forget this. (donning asbestosis causing flame retardent suit :-))