"Richard Clark" wrote

On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter"
wrote:
The shape of the pulse complicates the estimate because Duty Cycle is
often expressed in the expectation of a square wave. What is the on
time? When you get into pulse work, most in the field arbitrarily
assign the width of the half-power, or half-voltage points. For
Dave's numbers, this would be some 100µS which, when compared to 1
second is actually 0.01%. Being generous, and given the shape of the
decay I simply threw in a 10X fudge factor.

Thanks Richard.

- but then a 50kva strike would be

Meant to say "ka" sorry.

Dave - was that 500 amperes a typo or the figure used by the USAF
for protection design? My internal surge protection is designed for
10kva
max, and the rooftop downconductors would certainly be expected to carry
at
least 5x that much for a short time from a direct attachment. Even
internal
AC wiring is designed to carry 6kv/1kva before dialectric breakdown.
Which
does incidentally happen from those 100kva strikes. It just happened less
than half a mile up the beach from me last month.

You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether.

Only the those destructive MOV power strips get rated in joules ;-)

My normal-mode silicon diode surge suppression is rated in KA (not kva,
sorry again).

http://www.transtector.com/documents...s/1451-001.pdf

the 10ka model has a 12,000 amp surge rating. I located one at the main AC
entrance panel (load side) and one on the station's 240v branch panel.
Transtector also produces "power strip" surge protection that is all silicon
with NO MOV's and NO L-G references. My station has no AC surge protection
references to ground, and all equipment is connected to L-N surge protection
power strips. Except the computer which runs through an Amer.Pwr.Con. UPS -
which although it has an unavoidable L-G MOV, it is first protected by the
two Transtector Fortresses.

It just happened less
than half a mile up the beach from me last month.

No doubt, but what exactly was "It" that happened? Stick 50 feet of
tower up into the air, and interrupt it with insulation and YES! arcs
will spark. No one needs an insulated $$$$$$ tower - thousands of
commercial installations typically discard that feature in favor of
simple $$ lightning protection.

73's
Richard Clark, KB7QHC

A strike on a home and/or power lines in which the surge was so powerful
that it blew the electric meter clean off the wall of the home (burning the
powerline and the service panel inside the home). I visited when it was
still smoking but they discouraged my camera. I did get a good picture of my
neighbor's pine tree striped from 75' in the air to 6' above the ground,
where it jumped to and split a wood fence. That was about 50' from the end
of my 60 meter dipole which was operating at the time. I'm thinking the
surge protection is working as advertised this summer. At this rate I'll
soon have more examples that just nearby strikes......but hopefully not.

73,

Jack Painter
Virginia Beach VA