I agree that simply disconnecting the coax isn't enough, and that a quality
whole house surge protector is a good idea. It certainly can't hurt. But I
highly recommend designing the station so that *all* wires between the
tower(s)/antenna(s) and the building can be easily disconnected, with the
possible exception of the ground cables (see discussion below.) Belt and
suspenders are worth every penny.
12 years ago I had a lightning surge that caused over $10K in damage to $30K
worth of equipment (had I not done all of the troubleshooting and repair
myself, the bill would have been much higher.) Luckily, my home insurance
covered it. I've posted extensively on TT about that event, so I won't repeat
all of the gory details here, but wanted to point out that the strike did not
hit the tower. It hit a tree several hundred feet from the tower, and the
damage was caused by an induced surge. Damage on the tower was pretty minimal
-- just the destruction of four relay diodes in the stack match and complete
vaporization of a wide ground trace on its PCB (the only place where I found
any scorch marks or physical evidence of the surge.) Other than that, none of
the hardline, coax, cables or antenna switch relays were damaged. FWIW, the
shields of all the hardline and coax were bonded to the tower at the top and
bottom, and the relays were configured to be open rather than shorted when not
selected. None of the 24 SteppIR motors and none of the four rotors on the
tower were damaged. The rest of the damage was indoors, as described below.
The tower that took the surge has a Ufer ground with three 50' radials of 1/0
buried stranded cable, each Cadwelded to four 8' ground rods spaced 16' apart
(12 rods total). As it's 225' from the shack, there's no ground cable running
between the tower and the SPG at the shack entrance (Polyphaser says that past
75' the grounds don't "see" each other.) That said, there are two runs of
1-5/8" heliax between the tower ground and shack SPG, and the huge corrugated
copper shields probably have much lower inductance than a 1/0 ground wire. So
if the grounds can see each other past 75', I think they're pretty-well bonded
together. I have bulkhead Polyphaser coaxial surge suppressors for every RF
cable mounted through the bottoms of metal utility cabinets at both ends (tower
and SPG), as well as panel-mounted surge suppressors in the utility boxes with
two MOVs and a fuse on both ends of each control wire. All shields and ground
wires are grounded at both ends. The tower and SPG ground syste
ms are bonded to the metal cabinets via 1/0 stranded wire. The SPG is also
bonded to all the other ground systems that enter the house -- telco, cable,
satellite, electric. Unfortunately, they external drops for those grounds are
on the other side of the house, so I had to run the bonding cable from the
utility cabinets directly a cross the basement ceiling to the utility entry
panel. It wasn't clear to me that installing a couple hundred feet of ground
wire around the house with 15-20 ground rods Cadwelded to it was a better way
to bond the grounds. Open to discussion on that.
My theory on how the destruction occurred is that the surge was handled by the
coax surge protectors, and most of the MOVs, but the MOVs connected to my three
SteppIR controllers were of too high a value to protect the delicate ICs. They
were more suitable for protecting old-style rotor controllers, which didn't
have any delicate ICs. As it was, the motor control FETs in my three Green
Heron controllers were destroyed, but I believe the GH circuit design is such
that the FETs acted as fuses to protect the CPUs and other electronics. Not so
the SteppIR controllers. Their delicate SMD driver chips were fried, and the
surge made it past them to the RS-232 transceiver interface. From there it got
to the computer, destroyed the motherboard, CPU and multiport RS-232 card, and
then propagated to every device connected to that card, including a Ten-Tec
Orion (totaled), an Alpha 87A (RS232 IC fried and CPU partially damaged) an
Acom 2000A (RS232 IC and CPU fried), a MicroHam StackMaX controll
er (totaled), a W5XD keyer (RS232 IC and CPU). The StackMax could have been
damaged by the voltage threshold of the MOVs in the suppressors being rated too
high. I also lost the RS-232 level converter between an FT-1000D and the
computer, but there was no damage to the radio. Evidently, the level converter
saved the radio.
I also had damage to a very expensive high-end CD player, a C/Ku-band satellite
dish LNB, a C/Ku-band 4DTV satellite receiver, a C/Ku-band satellite TV DVB PCI
card in the computer, a Dish satellite receiver, a garage door opener, a phone
line, a digital scale (totaled via RS232 from the computer), and a ROKU media
processor. I believe the damage to those devices came via the C/Ku-band
satellite TV DVB PCI card in the aforementioned computer, which was on the same
PCI bus as the RS-232 card. It's possible the surge was picked up by one or
both satellite dishes, damaging the entertainment system devices and
propagating to the computer via the DVB card, and to all the station devices,
but given the damage and the destruction of the SteppIR and GH motor drivers, I
think it was the other way around (or maybe both.) No power supplies were
damaged, and no devices outside the shack and entertainment center were
damaged, except the garage door opener and telco line. I've lost several garage
door openers after lightning storms, and have read that they're quite
susceptible to lightning (I suspect the long wires to the manual switches acts
like an antennas.) The damage to the telco line was outside the house, so
evidently it picked up the surge there and the indoor suppressors did their job.
After repairing all the damage, I designed and installed a large patch panel so
I could quickly disconnect the many cables between the tower and shack. It
wasn't feasible to locate the panel outside, which would have been preferable,
so I installed it in a basement closet. All the cables passing through the
utility cabinets that are connected to the SPG enter the house just above the
sill, easily routed down to the panel. The station side cables run from the
patch panel up through the basement ceiling into the shack. There are about 20
or so cables on the patch panel, most of them multi-wire. It takes about five
minutes to disconnect all of them. I also installed electrical disconnect
panels so I can quickly cut off the shack circuits from the house AC. My two
amps and a couple of power supplies, routers, etc. are also located in the
closet, where I can quickly unplug them from the AC as well.
I built a smaller panel on the other side of the wall behind our entertainment
center so I could disconnect it from the rooftop TV/FM and satellite TV
antennas, and there's also an AC disconnect box in there.
Normally, I leave all the cables disconnected when the station isn't in use. I
only disconnect AC and TV cables when we go on vacation or there's a really
nasty storm in the area.
Note that I replaced the MOVs in the surge suppressors connected to the SteppIR
and (I think) GH controllers with MOVs that have as low a value as I could get
without going below the operating voltage of the driver outputs.
This setup has worked well for 12 years, but I hasten to point out that
although we've had our share of lightning storms since then, our area isn't
prone to them and we haven't seen anything near as nasty as the one that hit my
station in 2007. So I'm not resting on my laurels and am always on the lookout
for anything I can do to reduce the risk of lightning damage.
[BTW, if TT was on groups.IO, as I've pleaded for, I would be able to attach
photos of my patch panel, surge suppressors, tower, etc. And likely the text of
my post would have been shorter, one picture being worth the proverbial 1,000
words!]
Hope this is helpful to someone.
73, Dick WC1M
-----Original Message-----
From: john@kk9a.com <john@kk9a.com>
Sent: Wednesday, September 4, 2019 11:45 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Grounding
GL rebuilding Keith.
A tower lightning strike will cause an induced voltage spike in a
home's electrical system, even if nothing is connected to the tower.
I have had this occur while building a new tower and the control cables and
coax were not yet connected or even touching the tower.
Simply disconnecting the coax which many hams do is ineffective lightning
protection. There is a lot of valuable protection information on this list.
Assuming that you have a bunch of ground rods and a SPG, I would suggest a good
whole house surge protector.
John KK9A
from [Keith Dutson] NM5G
My experience is that lightning can be managed, to a point. A direct strike to
your tower can be catastrophic. I suffered one on May 9. My daughter lives
about 600 feet away and witnessed the strike. She said sparks flew in all
directions. My losses are huge. I am working with the insurance company, and
expect the total damage to be well in excess of $50K. There is evidence that
high voltage appeared on the tower, power lines, phone lines
(fiber) and even on my wi-fi connection from the house to the shack. Every
gigabit switch was toasted, and every PC connected was blown. Another big loss
was two large screen TVs, both connected to internet via gigabit switches.
Repairs were successful by replacing the power supplies.
All this, plus my main two stations, both with Yaesu FTDX9000D and Alpha 87A,
are gone. Coax was not even connected because I had just reconfigured the
station and had not completed the coax switching section. However, units were
plugged into power, and the Yaesu transceivers were connected to the PCs.
73, Keith NM5G
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