I don't know whether the cow/lightning story is real, but the premise is
valid and well-known. There have been documented cases where horse-mounted
police had their horses die under them as they approached an electrical
source that was shorted to ground. The electrical potential radiated out
through the soil from the power source, high near the source and lowering
as the distance increased. Since a horse's front and rear feet are
relatively far apart, as the horses approached the electrical source, the
potential under their front and rear feet was sufficiently different to
cause a current flow through their body that killed them. In one incident,
two horses died before someone realized what was happening.
The whole idea of a common point ground is to remove this potential (no pun
>Date: Fri, 14 Mar 2003 21:31:39 -0600
>From: "Jim Miller" <JimMiller@STL-OnLine.Net>
>Who was watching to see that the cows that survived were indeed standing
>broadside to the tree. They would have certainly moved before anyone would
>have seen anything. Sounds like a possibility but likely with little
>evidence other than the dead ones would probably not have gone far, hi.
>73, de Jim KG0KP
>----- Original Message -----
>From: "Roger D. Johnson" <firstname.lastname@example.org>
>To: "Rob Atkinson, K5UJ" <email@example.com>
>Sent: Friday, March 14, 2003 4:20 PM
>Subject: Re: [TowerTalk] Shack ground disconnect?
>> I remember hearing a story about some cows sheltering under
>> a tree during a thunderstorm. Lightning struck the tree and
>> the cows facing towards or away from the tree were electrocuted
>> while those broadside to the tree were not. The explanation was
>> that, as the charge dissipated through the ground, the cows
>> facing toward or away from the tree had their front and rear
>> hooves on ground of much different potentials. Those broadside
>> has much less difference between left and right side hooves.
>> I would think that a wire connected to a ground rod under these
>> conditions would behave much the same. If the equipment in the
>> shack had no other current path, nothing would happen as they
>> would all rise to the same potential simultaneously. However,
>> if there was another path to ground, it could have a vastly
>> different potential and sparks would fly.
>> Ask me sometime about the Great Lightning Disaster at the LORAN
>> station I commanded. It was caused by the Coast Guard insistance
>> on separate ground systems for the transmitter and timing equipment.
>> 73, Roger
Dick Flanagan W6OLD NV SM