[TowerTalk] Disconnecting cables and lightning (questions -- too long)

[Tyler Stewart]

Pete, I'm with you all the way.  For my money, disconnecting everything is
much more valuable than a pile of lightning protectors and grounds.

73, Ty K3MM

-----Original Message-----
From: Pete Smith <n4zr@contesting.com>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Thursday, May 07, 1998 13:49
Subject: [TowerTalk] Disconnecting cables and lightning (questions -- too
long)


>It's lightning season again around here, and ...
>
>Polyphaser and ICE make much of the ability of their line protectors,
>properly installed, to protect against lightning hits even if the lines
>remain connected throughout the event.  This is obviously relevant for
>repeaters and similar systems which must remain operational.  But recently
>I mentioned in an item printed in Hints and Kinks that in addition to using
>a ground bulkhead, I routinely disconnect all conductors coming from
>outside, in the belief that this, combined with effective grounding of the
>tower, would protect against lightning coming in on those conductors.  The
>editor of H&K found it necessary to add the words "only slightly," and that
>raised my curiosity.
>
>As I understand the physics from the Polyphaser book and discussion on this
>reflector, when lightning strikes a tower or antenna it, and anything on
>it, is immediately raised to a very high voltage.  How quickly this
>dissipates, and where the current flow goes, depends on the configuration
>and execution of all of the grounding provisions, including the tower base,
>the house electrical service, and the station equipment.
>
>Fine so far.  But if the base of the tower is well grounded (multiple rods
>and radials, properly connected to the tower base), but it's several
>hundred feet from the tower base to the house, I question whether it's
>really possible to keep that ground and the house ground at the same
>potential, with any reasonably-sized conductor between them.  Moreover, my
>shack is on the second floor, which would make it very hard to have a good
>low-impedance ground connection at the bulkhead.  Now if I disconnect all
>the conductors (coax, rotor cables, etc.) and maintain a several-inch air
>gap, it seems to me that a very high proportion of the strike current
>should flow down the tower into ground, and that the length and
>configuration of my long cables should provide sufficient inductance to
>keep the voltage at the bulkhead from rising high enough to arc across to
>the inside cables lying nearby.
>
>Finally, my questions--
>
>1.  Am I wrong?
>
>2.  Would I be better off grounding each of the conductors coming from the
>tower at the entry bulkhead, instead of letting them float, as now, even
>though I know the grounding of the bulkhead is relatively poor in terms of
>inductance?
>
>3.  What about a disconnect and/or grounding panel at ground level, near
>the AC service entry?  Worth doing, for the sake of the better, and more
>unified ground?
>
>4.  Some people have written here recently about cable grounding schemes
>using relays to switch their cables from the shack to ground.  It seems to
>me that with the close spacing of relay contacts, the ground they're
>switching to better be pretty darned good, or arc-over and equipment damage
>will occur regardless.  Wrong again?
>
>Thanks for all the anticipated good advice.
>
>
>
>
>73,  Pete Smith N4ZR
>In wild, wonderful, fairly rare WEST Virginia
>
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