[BC] Lightning and grounding - tower differences matter?

[Phil Alexander]

On 19 May 2005 at 7:55, Barry Mishkind wrote:

> At 04:26 AM 5/19/2005, Alan Alsobrook wrote
> >I can't say it does or it doesn't, but it sure seems to help. In the poly 
> >phasor document you have provided, it indicates that a ground for the 
> >array may not have been provided. What I know of the dissipater systems 
> >they don't work without a very solid ground. Also if you properly install 
> >them you will have also provided a way to control a strike should it occur.
> 
>          Alan,
>          Are you saying that it is your understanding that
>          this sort of prevention will work on an FM or
>          grounded AM tower only, leaving insulated
>          towers out of this part of the discussion?

Barry,

For towers (and I restrict this to towers alone) there may be some value
in what Alan is calling dissapater systems, but caution is necessary.

With the warning that my understand may not be totally correct, here's
my take on this issue.

If ESE/CTS devices work, and there is a great deal of scientific evidence
that says the are essentially snake oil so far as lightning protection
is concerned, the only place where they appear to have some value is in
REDUCING, NOT ELIMINATING, the number of hits on towers.

When one of these devices IS HIT by a stroke, they are no better than a
Franklin rod, and may not be as good. However, if you talk to TV guys in
heavy lightning areas you can find quite a few success stories where they
have very significantly REDUCED the number of strikes. You can also find
documented cases where they have failed miserably in industrial plant
protection service, and have been removed as a result.

However, the professional lightning protection community ably represented
by Dr. Mousa, Richard Kithil and others, are aggressively opposed to these
devices, apparently for several reasons that, IMHO, are quite correct. These
reasons concern the GENERAL application of the devices, rather than their 
application for strike event reduction on broadcast towers.

The ESE/CTS devices are outrageously priced compared with Franklin rods
and are frequently promoted as "protecting" a much larger area than an
ordinary rod. If these devices were installed with conventional Franklin
rod spacing, any project using them would become almost prohibitively
expensive. Thus, the claims appear essential to the their sale in the 
general lightning protection market. The wide area claims DO NOT appear 
to be supported by any kind of rigorous science. Thus, the sale of these 
"gadgets" has left unsuspecting property owners very poorly protected, if 
"protected" can be used in this sense. Thus, it is right and proper IMHO 
that these things should have no official standing as an approved device 
by any authority. In fact, both the NFPA and IEEE HAVE DENIED them 
recognition, yet they seem to continue claims that such approvals are 
"pending." 

Looking at it from the outside, it appears to me that the apparent
dishonesty of the promotion of these devices is one of the reasons that
the issue itself is so polarized. The scientific fact appears to be that
there is no magic in these things, and for all practical purposes they
don't provide greater coverage than a Franklin rod.

However, the possibility remains that they may have value for REDUCING
the number of hits taken per year ON TOWERS. The fact of current flow
has been reported earlier in this thread, and the acceptance on tall
TV towers has been known for some time.

I've come to the point of believing they may have value on towers, but
I'd never use them for building protection, or anything else. I think
Cowboy made an excellent suggestion earlier in the thread when he said
he used charge dissipation devices and Franklin rods together on towers, 
and IMHO that may be the best way to do it.

When they are used, Alan's point about grounding and conduction from
ground to the device is obviously VERY important. A very low impedance
between device and ground is essential if they are to carry significant
"dissipation" currents. This suggest effective use may be problematic
with series fed AM towers, and also suggests a need for extremely good,
very low resistance bonding for grounded towers, as well as a very good
ground termination (IOW a pattern of long rods, and possibly chemical
augmentation).

Bottom line, on a tower, I think they are worth trying, but for anything
else - NO WAY. That's what Franklin rods are for. My $0.02 for the day.

Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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