I had 3 pieces of 1" braid in place to bond the rotating mast to the sleeve at
the top of my tower. A lightning strike burned all 3 into. Balled ends on
the strands confirmed this.
73
Bob
Sent from my iPhone
> On May 16, 2014, at 6:04 PM, Stuart Rohre <rohre@arlut.utexas.edu> wrote:
>
> Jim, don't we all use Flukes now? :-) I do have several at home and work.
> I was remembering a discussion of a rig fault where the pin intended for
> grounding, had not been grounded at the radio connector entry to chassis.
>
> Good point you make about low ranges needed for ohms measuring. There are
> some good build it yourself low ohms measuring circuits out there, to extend
> the range of an ordinary meter. The Graf (author) series of circuit diagrams
> books includes at least one. The ham magazines in last 40 years had one or
> more.
>
> In the midst of measuring things, most good troubleshooting includes a
> thorough visual inspection to see how things are bonded and grounded, and if
> the circuit board is providing the connection to chassis.
> Unfortunately, we had not done a pre service inspection of the following
> radio incident:
>
> For high current faults, we have seen a Yaesu 5100 that had RF connection to
> circuit board and its DC negative power line to same circuit board at other
> end of chassis. A lightning event on the tower induced shield current down
> the coax to the radio , across the circuit board, vaporizing part of the
> ground copper, and then to the DC negative line which returned to AC third
> pin and power supply chassis.
>
> The bonding was done by an experienced power plant engineer, but it provided
> an extra return path through that circuit board trace, that caused severe
> damage to the trace. Luckily, that radio has survived that, with a bus bar
> now bonding DC negative to the coax connector shell external to the chassis.
> (No longer relying on the radio circuit board traces.) The radio worked even
> after losing part of the board copper, but only if the coax was connected,
> which was grounded to the tower and earth providing a return through the AC
> third pin. That observation prompted us to open the radio, which then showed
> the missing trace.
>
> As for braid failures, literature about high current faults has stated that
> braid can blow apart in a near direct strike, as little shards of wire.
> Indoors in someone's shack that could cause injury, or put small shorts into
> places hard to find.
>
> Copper flashing could be used in place of braid. The use or either was to
> provide low inductance through wide flat conductors used for bonding
> equipment together.
>
> Stuart Rohre
> K5KVH
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