[time-nuts] Thoughts on lightning protection measures....

Bob Camp lists at rtty.us
Fri Apr 13 16:31:47 UTC 2012


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-bounces at febo.com [mailto:time-nuts-bounces at 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)
> SAIDJACK at 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
>

_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.




More information about the time-nuts mailing list