[TowerTalk] Grounds, 'remote' towers, 'house' power system

[David Robbins]

because of the rise time of lightning you will never get around the inductance unless you pave your property in copper... forget it.  all grounds must be connected
for power line safety, you don't want a fault in the house to cause power line voltage to appear on the shield of a coax or somewhere else that doesn't have a low
impedance (at 60hz) back to the house power panel to blow the breaker.  For lightning protection you want to use the single point ground concept to keep all the
wires at the same potential so there aren't paths back through your equipment for the lightning charge to find it's way in or out of the shack.

about charge being attracted to the tower by a storm, the more conductive you make your ground the more charge will go up the tower as the downward leader
from the lightning storm comes towards it.  tops of trees get less charge because of the higher resistivity of wood, even when wet... and because there are normally
lots of them sharing the charge in a given area under the cloud.


Jan 13, 2016 11:43:48 AM, rxdesign at ssvecnet.com wrote:

I’m a bit confused by the push to connect my tower to the house power coming in – direct of course ... but nonetheless connected. 

When I asked about ground rods from the tower legs it was stated, and I knew this coming in, that the inductance of the line out to the ground rods from the tower leg would dominate the response and usefulness of that ground rod... ok ... that makes sense... but there we’re talking about in most cases a strap – wide, flat, with few bends – i.e. an attempt at reducing the inductance of that connection... but going from the tower to the house – even for most where the tower might be 75’+ away (my furthest will be 300’, closest 150’) – using a at best #6 wire typically (I know – there are those that use bigger – I’m talking about the ‘norm’) .... THAT inductance is going to tremendously influence the response. The current through it during the “charging” phase – i.e. the stroke will be rising relatively slowly ... but if the pulse is long enough and you get enough current in that line when the pulse stops now the voltage instantly reverses going high at the house end... if the connection isn’t very sturdy (able to handle the current with low resistance/inductance) that voltage will be quite high. The connection from the power company system to the house is – again – maybe #1 aluminum cable... and it is often long as well... so IT isn’t going to add any low impedance path either. The house thus becomes isolated! 

I’d think the best way to do it would be to seriously ground the hell out of the tower – connect the cables that have shields including the coax to the tower at its base ... but DON’T connect the ground to the house! I’ve done this in many installations and haven’t had any problems. I do however disconnect my antenna coax anytime I’m not on ... I know I know – there are those that say “I never disconnect and haven’t had problems” ... but to me it’s a simple ‘improvement’ to the protection level. And I’m not referring to very large stations with 4 or more incoming coax lines – just the average with 1, possibly 2 or 3. 

Also: regarding a previous posters “cone of protection” comment.... I’ve always believed that if one has a good ground at the base of the tower and the tower is a large conduction path – i.e. low resistance/inductance to the top – then it will be more difficult to form an opposite charge at the top of the tower. Other things like trees – especially tall ones which are not overly conductive will more easily establish an opposite charge at their tops and thus form a more attractive point of discharge for the lightning. I’ve had tall towers – and as far as I know never had a direct hit to the tower. Any issues I’ve ever had were power line induced – coupled energy from other close strikes. 

sent previously:
There is considerable confusion here with respect to radial systems forantennas and an earth connection for lightning protection. They are VERYdifferent, and both are important. Properly bonded conductors buried in concrete ARE acceptable as a ground for lightning protection -- it'scalled a Ufer ground, after Herbert Ufer who developed the concept, andit's now recognized in the National Electric Code. A Ufer ground worksbecause 1) concrete is conductive and 2) there is a large surface areain contact with the earth. The downside is that the earth it makescontact with is near the surface.Like ALL earth electrodes, it must be bonded to all other grounds inyour home -- power system, Telco, CATV, your shack, and all driven rods.I think Bob is on a pretty good track with his design.For more ideas, see http://k9yc.com/160MPacificon.pdf73, Jim K9YC
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