Hi Bob,
When I had my lightning protection survey done on my house,
there was a requirement that all of the lightning grounds
be tied to the power, telephone, cable, and water grounds
at a single point. Before I did this, I lost modems, network
cards, fax machines, etc.. afterward, no problems.
I do lose the occasional phone surge protector in the network
interface block, but they seem to do their job, and protect
everything else.
-Chuck Harris (knocking on wood!)
Bob Camp wrote:
Hi
Yes indeed, very true.
Things like telephone lines and cable lines need to "jump" at the same time
as the house ground. The fact that they don't is what makes cordless phone
base stations, modems (remember them?) and cable boxes the main victims in
lightning hits.
Bob
-----Original Message-----
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Chuck Harris
Sent: Friday, April 13, 2012 9:14 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thoughts on lightning protection measures....
As the power line worker strapped to the million volt wires he is
working on shows, what is important is that all the grounds in the
house stay at the same potential... not that they stay at some
perfect earth ground potential.
It really doesn't matter if a "house" ground jumps up many
thousands of volts for an instant during a lightning strike, as
long as everything electronic in the house, and everything
structural in the house jumps too.
-Chuck Harris
Attila Kinali wrote:
Moin,
On Thu, 12 Apr 2012 18:28:24 -0400 (EDT)
saidj...@aol.com wrote:
if I remember correctly, the issue is that the "ground" at the house is
not a "real" ground when the earth is frozen, as the resistance of frozen
earth goes up substantially over non-frozen earth. So it's like not
having
grounded the wires at all.
Yes, that's why in Switzerland you have to bury the grounding loop/wires
at least 1m deep (IIRC), in cold areas even 1.5m deep(again IIRC) to
ensure
that the earth never freezes.
I would have assumed that the building rules in the north have similar
requirements, just with deeper digging.
Of course, if you live on permafrost, you will never have a decent ground
:-)
This is a real issue for cables brought to the house (cable TV,
telephone,
etc etc) as those cables are grounded somewhere else on the other side,
and
thus there may be 1000's or even 10000's Volts between the two
"grounds",
even (or especially) for just a proximity strike. As mentioned by
someone
else, all bets are off anyway's for direct hits, not much will survive a
direct hit.
Well.. if you have a near hit on some long cable. you're lucky if the
attached electronics survive. But it shouldn't kill everything in the
house. My point was that, with "proper" ground connection, your house
potential should increase to "many 1000s of volt", even with a near hit.
Again, i might miss there something.
It's been a long time since I designed cable TV receivers, but the specs
are here, and I think there are some explanations in there somewhere:
_http://www.nordig.org/specifications.htm_
(http://www.nordig.org/specifications.htm)
Thanks, i'll have a look at those.
Attila Kinali
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