[TowerTalk] my long lightning story (was RE: lightning strike)

[K4SAV]

That was an interesting story Dick. Thanks. K8RI suggested maybe induced 
currents from the strike, but it seems to me that you had more damage 
than what usually happens from that.  Here is one more possibility.  I 
have had this one happen to me.  When a strike happens very close, there 
is also the possibility of a secondary finger splitting off from the 
main stroke path and hitting other things close by.   In my case one of 
those secondary fingers hit my chimney which has a metal casing.  It 
traveled down that metal casing until it got to some AC wiring that was 
run in the wall just behind the casing.  At this point the lightning is 
on the AC wiring inside the house trying to find a way to a ground.  
This effectively bypasses all lightning protection devices, and a lot of 
damage happens even though it is small compared to the main stroke 
path.  Its easy to overlook these small paths when the big path is so 
obvious.

Jerry, K4SAV

Dick Green WC1M wrote:

>For 10 years I thought I could protect my station from anything but a
>superstrike, but that was before I put up a 110' tower, and before the
>summer thunderstorms around here became more violent (Climate change? Who
>knows?)
>
>Previously, all I had was my 72' tubular crankup, almost always retracted to
>22', a 75' AB-577, two 48' AB-577s, and several wires antennas strung in
>trees at the 65'-75' level. All the "towers" are either below the level of
>nearby trees or close to it, and all are at least 30' below the tops of
>trees on the high points of our land. The crankup has an extensive ground
>system, 12 ground rods spaced 12' apart, Cadwelded to four radials of 1/0
>wire attached to the base mounting bolts. There's a utility cabinet next to
>the tower with Polyphaser coaxial suppressors for every antenna and
>Polyphaser rotor suppressors for all control cables. All wires run to the
>shack through 265' conduits buried 4' deep, and there's a length of 1/0 in
>the bottom of the trench for the entire length. At the shack end, there's an
>identical utility cabinet with an identical set of suppressors. The panel in
>the cabinet is attached to a single point ground. The long buried piece of
>1/0 is also attached to the SPG. There's a copper bus bar running along the
>wall behind the operating desk to which all equipment is grounded, with
>individual leads, and the bar is bonded to the SPG. The SPG is also bonded
>to the AC and telco grounds (through the house, unfortunately, but that was
>the only practical way to do it.)
>
>The only problem I had with this system was a pair of CMOS NAND gates in a
>homebrew antenna switching system blowing almost every time we had a
>significant lightning storm. I suspected a bad MOV in one of the Polyphaser
>rotor control suppressors. I replaced it, but decommissioned that switching
>system before I had a chance to prove it was in fact a bad MOV. More on this
>later.
>
>Almost a year ago, I completed 110' of Rohn 55 with a 40-2CD at the top and
>a 3-stack of 4-el SteppIRs. The ground and lightning suppression system is
>similar. The pier contains a Ufer ground, which was required by our local
>electrical inspector. The rebar is wired together and 50' lengths of 1/0
>wire are clamped to the rebar and run out through the sides of the block
>about 2' below the surface in a radial pattern. Each radial leg is Cadwelded
>to an 8' ground rod every 16' (four rods per leg.) The tower end of each
>radial runs up through the concrete block and out the top, where they're
>clamped to the tower legs (it's a pier-pin foundation, not a buried
>section.) There's a utility cabinet at the bottom of the tower with a
>Polyphaser coaxial suppressor for each coax or heliax run, plus K5FD
>lightning suppressor boards for all control leads (96 at present, requiring
>eight 12-position boards -- the SteppIRs, TIC rings, stack match and SO2R
>switch require a lot of wires!) The cables run down into the ground through
>a short piece of conduit, where they run direct-buried about 2' down 225'
>back to the shack (no conduit this time.) RF is carried by two 1-5/8" runs
>of heliax. I didn't lay a long 1/0 wire in the trench this time to connect
>the tower ground with the SPG because I figured the massive outer conductors
>of the two heliax runs would provide a much lower impedance path to ground.
>Besides, Polyphaser says the ground systems won't "see" each other if
>separated by more than 75' because of the inductance of the wire (some
>disagree with this.)
>
>There are a few pictures of the 110' tower system on my website at
>www.wc1m.com. They're not complete, but do show the cable connections and
>ground system.
>
>All shack and entertainment system devices are connected to surge
>suppressors. These aren't the high-end ones recommended by (I think) by
>K9AY. The computer is on a UPS with surge suppressor, but it's not one of
>the super high-dollar units either.
>
>Less than a month after completion, we had the most violent lightning storm
>I have seen in 37 years of living in West Central NH. The storm began with
>no warning -- absolutely clear skies. The lights in our house got *very*
>bright, then we lost power (it was out for 13 hours.) Evidently, this was
>caused by a strike at a distant power substation. The first wave of the
>storm came up suddenly after that, but the lightning wasn't particularly
>violent or close. It was pretty typical for what we see in this area. We're
>far from any large body of water and the mountains tend to break up storm
>systems as they travel over the region. It's relatively rare for us to see
>large cloud-to-ground strokes. This first wave passed (the power was still
>out), and I went into town to get some take-out. Most of the town and
>surrounding region was without power (except the part with the take-out
>restaurant.) At the time, I noticed bright flashes and rumbling thunder far
>to the south and northeast, suggesting that the storm had already passed
>over us. I didn't see anything to the west, which is where most of our
>weather comes from. I got home with the take-out, and as we were eating
>dinner, a *huge* lightning storm hit very suddenly. There were very bright
>flashes and booming, cracking thunder, and the strikes moved to within a
>mile or so of the house. I was just getting my head around what was going on
>when there was a tremendous flash and crack of thunder very near the house.
>We heard loud cracking noises, like gunshots, from behind the entertainment
>center. I wasn't in the shack, so I don't know what sounds or flashes may
>have occurred there. I wasn't looking out the window, so I don't know if the
>new 110' tower got hit. I'm pretty sure another lightning strike hit
>something in the woods behind the house, maybe a tree.
>
>When the power came back on in the morning, I heard a loud buzz coming from
>the entertainment center. It sounded like an alarm clock. It was coming from
>inside a high-end CD player that's designed to be on all the time. I killed
>the power switch and the buzzing stopped. For the next few hours, I took
>stock of the damage. In all, I lost over a dozen pieced of electronic
>equipment, mostly ham gear. The damage included: my computer (dead
>motherboard and I/O cards), an Orion transceiver (deemed unrepairable by Ten
>Tec), an Acom 2000A amp (dead serial line drivers, dead CPU), an Alpha 87A
>amp (dead line drive, bad CPU), an FT-1000D (no serial communications -- the
>RS-232 line driver in the W1GEE interface cable sacrificed its life for the
>radio), three 4-element SteppIR controllers (dead driver boards), two Green
>Herron rotor controllers (burned out FET drivers), a microHam Stack Max
>(dead RS-232 line drive and dead CPU), microHam Info Panel (dead ROM),
>microHam Stack Switch (on the tower -- four blown relay protection diodes
>and a vaporized PCB trace), a Writelog W5XD keyer (dead RS-232 line driver
>and dead CPU), a feedline connector to the 40-2CD at the top of the tower, a
>high-end CD player (bad D/A converter and other damage), a C/Ku-band
>satellite system (dead C-band LNB and servo motor), a garage door opener
>(bad encoder), a digital postage scale (connected to computer via RS-232),
>an HD media processor, a telephone surge suppressor (part of a wall-mount AC
>suppressor) and a phone line (blown apart on the pole.)
>
>In all, this equipment cost over $30K new, and the bill for damage came to
>about $10K. That was cheap: I diagnosed and fixed most of the gear myself
>and was able to get either free or inexpensive repairs done to the amps
>without shipping, by hand-carrying them in for repair.
>
>Remarkably, most of the equipment in the entertainment center survived,
>including a brand-new plasma TV, a Dish HD receiver, a tube pre-amp, a phono
>amplifier, a turntable,  two solid-state audio amplifiers, an FM tuner, a
>DVR, and several other pieces of gear. Only the CD player and HD media
>processor were damaged. 
>
>Except for the dead semiconductors, there was no trace of physical damage
>inside the house, such as melted metal, scorch marks, vaporized PCB traces,
>exploded semiconductors, etc. No power supplies were damaged. I still don't
>know what caused the cracking noises behind the entertainment center. It was
>probably exploding components inside the CD player. I thought it might have
>been the surge suppressors on 
>the AC outlets but their "protected" LEDs are still on.
>
>The K5FD boards have fuses inline with each conductor to protect against
>accidental shorts, and they were blown on all of the SteppIR leads, all of
>the TIC ring leads, most of the stack switch leads, and some of the SO2R
>switch leads. The SteppIR leads had 5A fuses, the TIC rings had a 5A on the
>motor leads and .5A on the pot leads and the switches had .5A fuses on all
>leads. More fuses were blown on the tower suppressors, but some were blown
>at the shack end, too.
>
>I'm reasonably certain that either lightning struck the tower, or it picked
>up a large EMP surge from a nearby hit, perhaps the one that blew the phone
>line off the pole (same direction as the hit I thought was in the woods
>behind the house.) It seems clear the bad connector at the junction of the
>40-2CD rotor loop and feedline was caused by a hit or surge at the tower,
>perhaps on the antenna itself (found a black carbon path between the center
>pin and shell when I sawed it in half.) Unfortunately, I had not grounded
>the feedline shield to the tower (it is now, top and bottom.) It also seems
>clear that the surge traveled through most of the control lines, which is
>why the fuses blew.
>
>My theory is that before the fuses blew, the surge hit the SteppIR
>controllers, shorting all of the driver chips, and found its way to the
>RS-232 ports connected to the driver boards. From there, it propagated back
>to the multi-port RS-232 card, destroyed the computer motherboard and all
>the I/O cards, and propagated back out the multi-port RS-232 card to every
>device connected to the computer via RS-232, which included the Orion, the
>W1GEE cable, the 87A, the 2000A, the W5XD box, the microHam Stack Max,
>digital scale, etc. The failure mode in all these devices was almost
>identical: the RS-232 line driver was blown, and in most cases the CPU was
>blown, too. In almost all these designs, the CPU is directly connected to
>the RS-232 line driver. The 87A was unusual in that its CPU was damaged, but
>only the I/O port connected to the line driver. Apparently, the I/O ports
>are individually fused in that chip. All the other CPUs were killed stone
>dead. The Green Heron controller FET drivers were damaged in a similar way,
>by a surge coming in via the motor control lines, but since they were not
>connected to the computer's RS-232 card, the damage stopped there.
>
>This is where the theory gets a little hazy. The C-band LNB was connected to
>three different satellite receivers, one of which was in the computer. It's
>conceivable lightning struck the 10' satellite dish, killed the C-band LNB,
>travelled back to the computer, killing the satellite tuner card, and
>propagated through the multi-port RS-232 card to all those RS-232 devices,
>then back out to the tower via the control lines. But I doubt it. The other
>two satellite receivers were not damaged at all. My guess is that the surge
>went the other way. When it got to the computer from the SteppIR
>controllers, it went through the satellite tuner card back out to the C-band
>LNB on the dish. It didn't kill the other satellite receivers because
>they're connected through DC-blocking splitters. Something similar happened
>to the HD media processor. Its Ethernet port was fried, which was connected
>to a LAN card in the computer.
>
>The biggest mystery is the CD player. It had to have taken a hit either on
>the AC line (perhaps when the lights got bright, then again when the big
>surge hit), the audio connectors going to the preamp, or the coaxial digital
>input from one of the satellite receivers. But none of the boxes at the
>other ends of those cables was damaged. Plus, the CD player was on a surge
>suppressor. Note that this CD player was replaced under warranty about 6
>years ago with symptoms suspiciously suggesting it had been damaged during a
>storm (they kept trying to repair it, then it would fail, so they finally
>gave up and replaced it.) I suspect the design is susceptible to lightning
>damage, but I don't know the entry mode.
>
>I'm pretty sure the AC surge killed the garage door opener encoder, but it
>might have been the flash that vaporized the phone line connection.
>
>Although a phone surge suppressor blew, none of the connected phone
>equipment was damaged, including a DSL modem.
>
>So, why didn't the K5FD surge suppressors protect my system? Well, I think
>they actually did. The SO2R switch lines terminate at open relays in the
>shack, so there was no path to ground. Since some of the fuses on those
>lines blew, I think the MOVs actually did conduct the surge on those lines
>to ground, causing the fuses to blow. The same thing must have happened with
>the microHam Stack Max controller, where the control lines are also
>terminated in relays that were open at the time (I believe the box was
>killed by the surge that propagated back out the computer RS-232 ports.) I
>suspect the MOVs may have conducted on most if not all of the control lines,
>which may be why there was no evidence of melting scorching etc. The fuses
>probably provided protection from that, too. 
>
>Unfortunately, the SteppIR and Green Heron controllers had delicate
>semiconductors directly attached to the control lines, and I suspect the
>MOVs didn't start conducting until the max voltage level of those
>semiconductors was exceeded. Remember those CMOS NAND gates in my old
>antenna switching system? They were the only semiconductors directly
>attached to the control lines, and they were the only parts that
>consistently failed during storms, despite being on surge suppressors. 
>
>Part of the problem is that all my K5FD suppressors had 82V MOVs in them
>(Polyphaser uses a similar value in their suppressors.) I'm sure this was
>too high for the driver chips in the SteppIR controllers. SteppIR later told
>me a value around 45V is best for MOV protection for the controller. The FET
>drivers in the Green Heron controllers can use the same value because the
>TIC rings run at less than 40V. K5FD has been great about helping me to
>replace or retrofit MOVs into the boards that more closely match the max
>voltage levels of the connected devices.
>
>However, after this experience, I'm not convinced this is enough. It's one
>thing to rely on MOVs to protect switches, relays and the old analog rotor
>controllers. But it's not clear to me that the semiconductors in more modern
>equipment can stand any reasonable level of voltage above their operating
>voltage. It may not be possible to find a MOV that will conduct at a voltage
>less than what it takes to kill the semiconductor without getting tripped by
>operating voltage spikes. If the device happens to be connected to other
>devices through a communications link, a lot of damage can occur if one of
>the semiconductors breaks down.
>
>For this reason, I finally decided to throw in the towel and construct a
>master patch panel for my station. With two separate SO2R switch banks,
>seven rotors, three SteppIRs, a stack switch and numerous coax runs, the
>cabling inside the shack is very complicated and its tough to get to all the
>cables to disconnect them, let alone getting to all the outlets behind the
>desk to unplug the equipment. I had previously moved my autotune amps to the
>basement under the shack, where the cables enter the house, and we had built
>a closet around it. I moved the rest of the switching control gear
>(PC-controlled, Ethernet-based) to the basement, and built a patch panel
>containing plugs for every single line that comes into the house from the
>tower, including coax, switches, relays, stack switch, SteppIRs, rotors,
>etc. I also installed a disconnect for three phone lines coming into the
>shack and a Dish satellite TV antenna. I relocated the 220V outlet so I
>could quickly disconnect the amps from AC, and also installed AC disconnect
>panels for two AC lines running into the shack. So, except for SPG and AC
>ground, the equipment in the shack can be disconnected from everything else
>(there are about 35 cables to pull.)
>
>I plan to install a similar set of panels in the basement underneath our
>entertainment center, to cut off the rooftop antenna, C-band antenna and AC
>power.
>
>I'm not taking out the suppressors, of course. I think they still provide
>valuable protection for all the cable runs, and will provide some level of
>protection if a storm comes up suddenly when I'm operating or if I forget to
>disconnect everything at the patch panel.
>
>[The only question in my mind is leaving the equipment connected to the AC
>and SPG grounds. I worry about the ground system not being able to absorb a
>direct hit or superstrike. Then again, I think the equipment would have to
>be connected to some lower potential for the surge to find a path through
>it, and I think I've eliminated that possibility. Anyway, if I had my
>druthers, I'd disconnect the grounds, too, to have the equivalent of putting
>each piece of equipment back in its shipping carton. But the available AC
>disconnects don't provide for ground to be disconnected, and it would be
>pretty hard to devise a quick disconnect for my SPG.]
>
>So, that's my story, and I'm sorry it was so long and detailed. It's been a
>real watershed event for me to have converted from "B/C stations stay on the
>air during operation, so I can too" to "Disconnect everything." All it takes
>is one bad experience.
>
>73, Dick WC1M
>
>
>  
>
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