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Author Topic: Coax routing and grounding  (Read 6564 times)
K1CJS
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Posts: 5875




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« Reply #15 on: August 05, 2013, 04:44:42 AM »

....The only point of the single point ground system for home use is to allow it to be bonded to the service entrance ground, regardless of how 'good' it may be, so that extraneous currents can't be induced to flow between the antenna system and the house AC system.  Ain't trivial and certainly not meant to guarantee no damage in the event of a direct strike but it should guarantee minimal damage.  This assumes of course a nearby strike doesn't induce a severe transient on the power lines coming into the house, another problem altogether.  I haven't addressed that yet although I did request it from our utility company but no surprise, no reply.

And this is somewhat of a fallacy in itself.  How many times has a report been made of a lightning strike 'jumping' from a known electrical path to a random metal pathway that has no relation to the electrical ground itself?  There are so many potential ground points in a home that 'single point' ground system protection is improbable at best.  Buried water lines, although most are plastic or PVC now, buried gas lines, buried telephone and cable lines, heating systems, heck--even iron/steel support posts buried in a concrete basement floor!  There is absolutely no way to achieve a true single point ground for a building unless you were to insulate that building in every way from all surrounding conductive materials.  A lightning charge is unpredictable and may well jump from point to point even if you provide an optimum pathway for it to follow.

As I've already said, if you sustain a lightning strike, you're going to have damage--and a single point ground system as you suggest won't stop the charge from going through your house if it 'sees' an optimum pathway that you didn't anticipate at all.  After all, that charge just came down through hundreds of feet of air.  It may well ignore that 'single point ground' and hit at some other metal point around or in the building.  73.

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AD5HD
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Posts: 14




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« Reply #16 on: August 05, 2013, 03:15:43 PM »

....The only point of the single point ground system for home use is to allow it to be bonded to the service entrance ground, regardless of how 'good' it may be, so that extraneous currents can't be induced to flow between the antenna system and the house AC system.  Ain't trivial and certainly not meant to guarantee no damage in the event of a direct strike but it should guarantee minimal damage.  This assumes of course a nearby strike doesn't induce a severe transient on the power lines coming into the house, another problem altogether.  I haven't addressed that yet although I did request it from our utility company but no surprise, no reply.

And this is somewhat of a fallacy in itself.  How many times has a report been made of a lightning strike 'jumping' from a known electrical path to a random metal pathway that has no relation to the electrical ground itself?  There are so many potential ground points in a home that 'single point' ground system protection is improbable at best.  Buried water lines, although most are plastic or PVC now, buried gas lines, buried telephone and cable lines, heating systems, heck--even iron/steel support posts buried in a concrete basement floor!  There is absolutely no way to achieve a true single point ground for a building unless you were to insulate that building in every way from all surrounding conductive materials.  A lightning charge is unpredictable and may well jump from point to point even if you provide an optimum pathway for it to follow.

As I've already said, if you sustain a lightning strike, you're going to have damage--and a single point ground system as you suggest won't stop the charge from going through your house if it 'sees' an optimum pathway that you didn't anticipate at all.  After all, that charge just came down through hundreds of feet of air.  It may well ignore that 'single point ground' and hit at some other metal point around or in the building.  73.

Yes, absolutely true.  Lightning jumps in the strangest of ways and can cause damage regardless.  A single point ground per NEC is at least the minimum one should take but it doesn't guarantee no damage will occur sorry if it seems I implied it.  Minimizing damage it may do but it's really impossible to say just how minimal damage may be especially if one is unfortunate enough to suffer a direct strike.  The charge will go through the house and the potential differences and available surge currents will destroy pretty much everything, no doubt about it.  The only way to avoid it is either build a broadcast quality installation or don't own any equipment.

Half a loaf and all that I figure.  With all the elements in a real world house that concentrate fields and allow the air to be ionized into conduction to form many unpredictable paths there's only so much one can do, you're completely correct about that, lightning made it all the way down from the sky and it isn't likely to follow wiring only.  What little does follow wiring or gets induced in the wiring elevates the station where it's plugged in and should it be so great an energy at that point it will indeed arc to whatever can accept charge which is why all metallic objects are supposed to be bonded to a ground window.  But even then it offers only so much protection, as many unseen paths are easily overlooked.

I think we're really in agreement here, I'm just following the recommendations for best practices as reasonably as possible and fully understand the risks involved given its inherent limitations  without a true perimeter ground and all the ancillary protections available to further harden the station against damage.  And at some point the cost of protecting the equipment exceeds the cost of the equipment itself.  I'll be happy if a strike at least doesn't start a fire...  Smiley

Thanks for your input, it's very helpful and very much keyed to the real world rather than the rote methods found in various references.  73
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K1CJS
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Posts: 5875




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« Reply #17 on: August 06, 2013, 04:45:17 AM »

Yes, I think we are in agreement--finally.  As with everything else, it's all in the way the individual 'reads' the instructions and interprets them.  73.
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