On Jan 26, 9:25 pm, email@example.com wrote:
Here are some of your statements and some questions:
"Whatever you (Robert) say. You are obviously MUCH smarter than the
protection engineers that design the stuff. "
What exactly has Robert Macy said that is inconsistent with what
lightning protection engineers say?
"ALL of the farm lightning rod systems I've ever seen have used the
looase braid copper cable.(Class 1)
The two supplier links you yourself provided clearly offer lightning
that are *not* braided as well as those that are braided. They are
on the link next to the braided ones. That would surely
seem to suggest that despite what you might or might not have seen,
braided conductors are not used exclusively. So, what exactly is your
Interesting that with that cabling one only gets 50C rise for that
much current, but at least not enough to ignite anything. My
experience with ESD discharges [inside confined electrical systems] is
that the energy is approximately centered around 3MHz, extending very
energetically up beyond 30MHz, and in poorly designed systems above
100MHz. These ESD events are those little 'arc overs' in the 20kV, up
to 150kV systems.
I was surprised the coil's inductance measured around 50uH
But, I shouldn't have been surprised since a six foot length of Belden
Hospital grade AC line cord is a three winding transformer with a core
impedance measured approx 7uH. [That was from memory, may have been
1.7uH, 7uH seems a bit high, suggesting 100nH/in, where the usual is
only 10-20nH/in] If interested, a few years ago I posted the model
for the AC cord named with the Belden part number in the LTspice
group, along with a couple of standard LISN models.
On Sun, 27 Jan 2013 07:26:07 -0800 (PST), Robert Macy
A software developer I used to do contract work for had all kinds of
problems with their 10B2 ethernet network. Collision rates and
dropouts were HORRENDOUS. I found 50 foot rolls of co-ax coiled up
behind desks in a few spots, and MANY 15-25 foot rolls - "just in case
they wanted to move the desks". I took out all of those "air core
inductors", replacing with cables jus a foot or two longer than
absolutely necessary, and the network speed and reliability improved
On Jan 27, 12:04 pm, firstname.lastname@example.org wrote:
Well done! There is a way you could have kept all those cables and had
the best of both worlds. [as long as you didn't exceed maximum
distance] by using ferrite clamps on the cables. Just place every foot
along each cable and that would have destroyed the 'transformer'
effects. However, at $1/ea they probably would have opted for the
From personal conversations with the lightning expert from the Univ of Wisconsin electrical engineering department,
the wave form of the lightning strike is a damped sinusoid and the cable need only be #10 wire.
Now, nobody ever installs them with wire that small. It's counterintuitive. But this professor could back up his statements both with the math and with experience.
Some of you who've been around usenet a long time may remember some of the arguments over lightning striking cars. Yes, it protects, via the Faraday cage effect, but cars seem to get hit less often than they should, so maybe the shape is protective in some way.
But this professor could back up his statements both with the math and with
Part 1 of the article I linked to (which is no longer on line) has
temperature data for wires. A #10 wire has a 200 degree C rise for a
100kA lightning stroke. About 5% of strikes are over 100kA, and there
can be multiple strokes.
#10, or the house it is attached to, is likely to have problems in Florida.
A related factor, I would think, would be the voltage drop across
the wire. Assuming your 100ka strike, a 50ft run of 10gauge would
develop 5,000 volts. A 50 ft run of 4gauge would develop only 1,200
volts. At the higher voltage, the likelihood of the strikie flashing
over to something other than the desired wire increases.
On 1/29/2013 10:48 AM, email@example.com wrote:
But this professor could back up his statements both with the math and with
I assume that is based on resistance.
Lightning is a very short event which means it has relatively high
frequency components (from a previous post most of the energy is below
100kHz.). That means inductance is likely more of a problem than
resistance. Also skin effect. Larger wire has a major effect lowering
resistance, but not much effect on inductance and skin effect. Both are
covered in a link I posted.
Downconductors are #3 or larger. They are that large for reasons also in
a previous post.
================================================For power wiring, the 1968 NEC had correction factors for skin effect on
large wires. I don't know when the tables were dropped; the correction
was probably rolled into the other tables. The AC resistance of a 4/0
wire is increased by about 0.5% over the DC resistance. The diameter of
a 4/0 stranded conductor is about 0.5".
On Jan 28, 12:01 pm, firstname.lastname@example.org wrote:
Actually will help
prevents signals fromgetting onto the shield and then 'injecting'
themselves inside to the center conductor. Also makes the coax
'higher' quality.Work on analyzing 'shield induced' noise may appear
somewhere. The beads help prevent that.
On Jan 25, 11:00 am, email@example.com wrote:
Thanks. Robert always thinks his opinions are better than anyone
elses standard usage.
Most of what we used was the Thompson smooth weave. It made down
conductors easier to form in smooth turns/angles that met specs. Not
being smooth turns invited the lightning to jump off the cable to
nearby surfaces. That's more proof why it travels on the cable
surface rather than deep.
Actually that effect has nothing to do with whether the current is
traveling near the surface of the conductor or not. It's due
to the fact that sharp bends increase the impedance of the
conductor which becomes significant with the fast rise time
of a lightning strike. As the impedance goes up, it becomes
more likely that the lightning surge will find another path to
One has to follow what one thinks. If proven wrong, then change that
I have ALWAYS looked very closely at the empirical facts. After all,
science DESCRIBES observation, and does not DEFINE it.
What I described does NOT refute the installations you're familiar
with, rather supports them. Just modifies some of the underlying
principles, that's all. For example, skin effect of the cable requires
the cable to be large diameter to be effective - which it is.
Flexibility during installation requires the cable to multi-stranded -
which it is. I just pointed out that one should not go on to claim
that somehow multi-stranded is approximating what is known as a "Litz
In those Class I cables for installation the skin effect does force
the conduction to the outside surface of the cable, and akin effect's
increase in impedance actually justifies using the 'smooth' weave to
maintain lowest possible impedance. Not a bad compromise at all.
Just make certain that the grounding goes to ground and not to
something 'floating' above ground. There was an oil field in Kansas
that kept losing their down hole pumps due to lightning srikes. They
had all the 'right' protection possible around them but still during
heavy storms, they kept losing a pump. That means NO OIL, bring out a
rig, pull up the pump, replace - not cheap! pumps are what size? bore
diameter and almost 20 feet long?
I could NOT find anything wrong with their protection techniques, and
during pure frustration I started chatting with one of the drillers,
who decried that these wells were 'cursed' from the day they started
drilling, especially that damned wet salt layer they hit about 500
feet down. Say what!? Now just envision a large conductive salt layer
covering several square miles down around 500 feet. Any 'grounding'
you do up here on the surface is 'floating' in comparison. Solution -
drill down to the salt layers, ground all to that layer and problem
Lesson is 'never assume' and 'always listen'
At least one manufacturer of submersible water pumps puts surge
protection in the motor.
[I thought all oil well pumps were powered by surface walking beam.]
How do you connect to the salt layer given inductance of the conductor
I would think if the wells were steel cased to the pump, the casings
would not even work real well as a conductor.
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