I agree with Jeff. I have lightning suppressors on every cable and wire at
both ends. I recall reading a paper by the founder of Polyphaser
recommending suppressors at both ends if the cable run is more than 75 feet.
Above that length the cable inductance prevents the tower end from "seeing"
the shack ground, so there will be a difference in ground potential that can
cause damage to the cables at the tower end.
I have a lot of cables on the tower plus many relays, rotors and SteppIR
motors, so I felt it was worth having suppressors closer to those devices. I
built extensive ground systems at both tower locations on my property, plus
a single-point ground system at the shack end bonded to the utility grounds.
I also ground the coax cables at each antenna and at the bottom of the
tower, as recommended by every tower grounding paper I've read. I suppose it
wouldn't be a bad idea to have suppressors at the top of the tower to
protect those runs, but mounting them would require quite a bit of
fabrication, not to mention a lot of connectors and waterproofing. More
failure points.
That said, painful experience has taught me not to rely solely on lightning
suppressors. I think they're OK for coax and most switching and rotor
cables, but you have to consider whether the speed and voltage trigger point
of the MOVs is suitable for the equipment attached to the cable. For
example, the original SteppIR controller uses very sensitive driver chips
attached directly to the wires that run to the stepper motors on the tower.
It doesn't take much of a voltage surge to wipe out those chips. I found out
the hard way that the trigger voltage of the MOVs in the commercial
suppressors I bought was too high to protect the chips, which are very hard
to replace. Also, they didn't protect the FET drivers in my Green Heron
Engineering rotor controllers, though they're cheap and easy to replace.
I replaced the MOVs with units that have a lower trigger point, but after
$10,000 worth of lightning damage from a surge that travelled through the
SteppIR controllers to my computer and thence to just about every device
connected to the computer, I decided to build a patch panel so I can quickly
disconnect every cable (and there are a lot of them.)
FWIW, insurance covered almost all the damage, but it was a real pain to
troubleshoot and repair/replace everything. Took weeks and weeks.
73, Dick WC1M
-----Original Message-----
From: Jeff [mailto:keepwalking188@ac0c.com]
Sent: Friday, November 10, 2017 9:36 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Where to put Lightning Arresters
I put the arrestors at the coax feed points into my shack at the home run
panel location. And also out at the tower base on the termination of each
antenna stack feeder. The reason for that is I want to buy some insurance
in the case of my tower mounted switching and that expensive in-ground coax
run back to the shack.
The shields of the coax on the tower are bonded and hit the tower's ground
system but the center of each coax is left floating. My thinking is that I
prefer that suppressor take a hit and try to dump some of that HV on the
center of the coax to the tower ground as best it can there instead of
lighting up the tower switching and the coax back to the shack. Suppressors
are expensive but compared to the other stuff relatively easy to replace in
the event they die the lightning inspired death out at the tower.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Jim Brown
Sent: Friday, November 10, 2017 1:05 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Where to put Lightning Arresters
On 11/9/2017 2:49 PM, Joe Partlow wrote:
> Is it better to put lightning arresters at the base of the tower or
> the cable entrance at the shack or both?
The function of arrestors is to protect equipment by shorting the center
conductor to the shield. In general, lightning arrestors should be on a
panel that is bonded to every ground in your home and is as physically close
to ground as practical and as close to your rig as practical. For a shack in
the basement or on the first floor, the panel in or on the wall outside the
shack. Also, in general, coax should be bonded to the tower at the top and
at the bottom.
I wouldn't put an arrestor at the tower unless the antenna is connected to
active electronics at the tower.
73, Jim K9YC
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