[TowerTalk] What Killed the Computers? was: Re: Grounding of Amateur Radio installations

Jim Lux jimlux at earthlink.net
Sat Dec 9 00:45:04 EST 2006

At 04:56 PM 12/8/2006, WA3GIN in Alex. City, VA wrote:
>None damages as far as you know...solid state devices don't always die
>immediately...some fail months or years later from small burnt spots in the
>solid state material of the devices.  In other words the longevity of the
>device may be significantly reduced rather than experiencing an immediate

I imagine that the testing was sufficiently thorough to eliminate the 
"latent damage" issue.  I think it's more of a recognition of modern 
design practices so that the device can meet Part 15 conducted 
emission requirements. A filter that prevents EMI from being 
conducted out the power line also suppresses transients coming in.

>I use UPS on my end points (those boxes have the corcom type chokes and the
>30 cent MOVs, etc. Unlike you Jim we live in a lightning alley where
>voltages vary a lot.  I've replaced quit a few 130v MOVs and I'm happy to do
>it.  While my neighbors are replacing coffee makers, TVs, refrigerators,
>telephone answering machines, etc. I just plug-in another MOV ;-)

WHy not use 170V or 200V MOVs?  (125 Vrms line is in spec *1.4 for 
the peak voltage is 175 V)  You're looking to clip transients, not 
regulate down 130V line surges. (because an MOV is a terrible way to 
do the latter)

That's the recommendation of the folks who study this stuff, anyway.. 
Put the lowest voltage clipping at the service entrance, and put 
higher voltages on the point of use.  And, use gas tubes and a LC 
filter (on the line side) rather than an MOV.  The Gas tube works 
forever (no wear out) and the LC limits the surge current when it fires.


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