Antenna Lightning Protection

[W. eWatson]

I have a mast, rotor and yagi TV antenna on my roof. The antenna is
probably 15' feet above the roof. It has 12 or so large elements, and a
similar amount of smaller elements. There are three guy wires. It was
struck by lightning about eight years ago, and took out the rotor
control in the house. There was no apparent damage to the antenna it is
not in use, disconnected from the TV, but the antenna wire goes into the
house. It is easily the tallest structure around the house, that is, no
trees accept a tall pine about 80' away, which is close to the height of
the antenna.

About the end of August and to mid-Sept. we have occasional electrical
storms. We had a strong storm near our house 2 weeks ago. My question is
should I have the antenna taken down or somehow grounded. If the latter
what's a conventional way to do it? Copper wire from the base of the
mast down the side of the house to a ground pipe? The antenna is about
20' from the end of the roof near it. I'm not sure of the material used
for the mast. It may be aluminum.

 

[RobertMacy]

Take it down. It's an "attractive" nuisance ;-)

...Jim Thompson

I second that. Take it down. To understand why, remember what you just
described to 'protect' it, that is, make it grounded better?!
Big ouch.

Seriously, it's bad enough *IF* you must have that in the air, but to not
need it and leave it is, ...like an invitation. And believe me. you were
lucky to only have damaged the rotor last hit.

 

[operator jay]

I have a mast, rotor and yagi TV antenna on my roof. The antenna is
probably 15' feet above the roof. It has 12 or so large elements, and a
similar amount of smaller elements. There are three guy wires. It was
struck by lightning about eight years ago, and took out the rotor control
in the house. There was no apparent damage to the antenna it is not in use,
disconnected from the TV, but the antenna wire goes into the house. It is
easily the tallest structure around the house, that is, no trees accept a
tall pine about 80' away, which is close to the height of the antenna.

About the end of August and to mid-Sept. we have occasional electrical
storms. We had a strong storm near our house 2 weeks ago. My question is
should I have the antenna taken down or somehow grounded. If the latter
what's a conventional way to do it? Copper wire from the base of the mast
down the side of the house to a ground pipe? The antenna is about 20' from
the end of the roof near it. I'm not sure of the material used for the
mast. It may be aluminum.

IF you leave it up (which is probably the worse option) then I'd suggest you
run copper wire from the TOP of the mast, all the way down. Ideally this
'down conductor' (as some call it) has no sharp bends in it and preferably
no bends greater than 90 degrees.

I'm not 100% sure what you mean when you say ground pipe, but I would
connect the down conductor to a ground rod (10' long rod, steel or copper
clad steel depending whether your soil eats up unprotected steel, 3/4"
diameter, pounded straight down into soil until it's top is about a foot
below ground). Ideally that rod is 2m (or 4m or more) away from your
house's ground (be that a rod, underground metallic water pipe, or
whatever). You could then connect the ground rod to your ground system with
a #6 AWG bare copper wire.

j

 

[W. eWatson]

IF you leave it up (which is probably the worse option) then I'd suggest you
run copper wire from the TOP of the mast, all the way down. Ideally this
'down conductor' (as some call it) has no sharp bends in it and preferably
no bends greater than 90 degrees.

I'm not 100% sure what you mean when you say ground pipe, but I would
connect the down conductor to a ground rod (10' long rod, steel or copper
clad steel depending whether your soil eats up unprotected steel, 3/4"
diameter, pounded straight down into soil until it's top is about a foot
below ground). Ideally that rod is 2m (or 4m or more) away from your
house's ground (be that a rod, underground metallic water pipe, or
whatever). You could then connect the ground rod to your ground system with
a #6 AWG bare copper wire.

j

By pipe, I really meant about a six foot copper pipe, 1/2" or so.

Yes, taking it down the antenna seems a sensible way to go. I'll get
the fellow who put it together many years ago to remove it.

To Robert, a bad choice of words to Subject.

By the way the roof peak is about 60' long, and a roof, lower, is about
35' long.

So what's some simple way to protect us from being hit? Someone years
ago suggested four lightning rods strung out along the peak was a way to
go, with them all grounded. One end of the line along the peak would go
down the side of the house to the ground.

So is there

 

[operator jay]

By pipe, I really meant about a six foot copper pipe, 1/2" or so.

Yes, taking it down the antenna seems a sensible way to go. I'll get the
fellow who put it together many years ago to remove it.

To Robert, a bad choice of words to Subject.

By the way the roof peak is about 60' long, and a roof, lower, is about
35' long.

So what's some simple way to protect us from being hit? Someone years ago
suggested four lightning rods strung out along the peak was a way to go,
with them all grounded. One end of the line along the peak would go down
the side of the house to the ground.

So is there

Your reply looks to have gotten cut off.

If I understand correctly you have a peaked roof on which the peak is
60'long, and if you rolled down the slope away from the peak, you would go
over an edge, and drop onto another sloped roof. This lower sloped roof is
about 35' long, and sloped in the same direction as the higher roof. Also,
I have been assuming a shingle roof.

Yes, four lightning rods ("air terminals", probably about 20" tall each)
along the peak, with a conductor connecting them all, takes care of the
peak. Then, from the same end of the peak, two conductors could run down
the slopes from the peak to the edges of the roof (the conductors running
down from the peak would still be on top of the roof, but near the edge of
the roof). One conductor would go over the edge of the roof and down to a
ground electrode. The other conductor would go over the edge of the roof,
drop to the lower roof, run down the edge of that lower roof to a corner,
then go over the corner and down to a ground electrode. Those electrodes
should prbably be interconnected to each other, and to the house's ground.
The rods should be 2 or 3 feet out from the building.

I don't recall for sure, but I think you could probably do without the air
terminals - the conductor running along the peak acts as an "intercepting
conductor" and takes the lightning hit.

Take a look at this site, http://www.tlpinc.com/ Browse EVERYTHING under
"DOC LIBRARY" and I think you'll have a decent feel for what's going on.
The product catalogs under the doc library not only have the major
components, but also all the accessories and fittings.

I have no affiliation with that or any website or manufacturer. I know
those products and I think that site will be helpful to you.

Good luck.

j

 

[Bob Masta]

Your reply looks to have gotten cut off.

If I understand correctly you have a peaked roof on which the peak is
60'long, and if you rolled down the slope away from the peak, you would go
over an edge, and drop onto another sloped roof. This lower sloped roof is
about 35' long, and sloped in the same direction as the higher roof. Also,
I have been assuming a shingle roof.

Yes, four lightning rods ("air terminals", probably about 20" tall each)
along the peak, with a conductor connecting them all, takes care of the
peak. Then, from the same end of the peak, two conductors could run down
the slopes from the peak to the edges of the roof (the conductors running
down from the peak would still be on top of the roof, but near the edge of
the roof). One conductor would go over the edge of the roof and down to a
ground electrode. The other conductor would go over the edge of the roof,
drop to the lower roof, run down the edge of that lower roof to a corner,
then go over the corner and down to a ground electrode. Those electrodes
should prbably be interconnected to each other, and to the house's ground.
The rods should be 2 or 3 feet out from the building.

I don't recall for sure, but I think you could probably do without the air
terminals - the conductor running along the peak acts as an "intercepting
conductor" and takes the lightning hit.

I think you need the spiky rods pointing at the sky. The
purpose of "lightning rods" in this sort of installation is
not to conduct a hit, but to prevent it in the first place
by providing a drain for charge build-up. (There is a neat
high-school science experiment with a Van de Graaff
generator, where you tape a thumb tack to the globe with the
point outward... makes a definite "ionic wind" when charged
up!)

A system that is actually designed to conduct a strike (like
the Empire State Building) needs monster buss-bar to handle
the bazillion (or so) amps. <g>

Best regards,


Bob Masta

DAQARTA v7.40
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusic generator
Science with your sound card!

 

[Bill Gill]

I think you need the spiky rods pointing at the sky. The
purpose of "lightning rods" in this sort of installation is
not to conduct a hit, but to prevent it in the first place
by providing a drain for charge build-up. (There is a neat
high-school science experiment with a Van de Graaff
generator, where you tape a thumb tack to the globe with the
point outward... makes a definite "ionic wind" when charged
up!)

A system that is actually designed to conduct a strike (like
the Empire State Building) needs monster buss-bar to handle
the bazillion (or so) amps. <g>

Actually I just recently read a piece about how lightning
rods work, and that one said that your explanation is the
wrong one. They actually do catch lightning strikes, they
don't discharge the cloud to prevent them.

Bill

 

[Tom Biasi]

A system that is actually designed to conduct a strike (like
the Empire State Building) needs monster buss-bar to handle
the bazillion (or so) amps. <g>

1.21 Jigawatts.

 

[Massoud]

I have a mast, rotor and yagi TV antenna on my roof. The antenna is
probably 15' feet above the roof. It has 12 or so large elements, and
a similar amount of smaller elements. There are three guy wires. It
was struck by lightning about eight years ago, and took out the rotor
control in the house. There was no apparent damage to the antenna it
is not in use, disconnected from the TV, but the antenna wire goes
into the house. It is easily the tallest structure around the house,
that is, no trees accept a tall pine about 80' away, which is close to
the height of the antenna.

About the end of August and to mid-Sept. we have occasional electrical
storms. We had a strong storm near our house 2 weeks ago. My question
is should I have the antenna taken down or somehow grounded. If the
latter what's a conventional way to do it? Copper wire from the base
of the mast down the side of the house to a ground pipe? The antenna
is about 20' from the end of the roof near it. I'm not sure of the
material used for the mast. It may be aluminum.

If there is no tall structure around, why the antenna is 15' high on the
roof? you dont gain anything (the sight angel may not change more than a
degree) lower it and let the pine tree get zapped.










--- news://freenews.netfront.net/ - complaints: [email protected] ---

 

[Michael Black]

Actually I just recently read a piece about how lightning
rods work, and that one said that your explanation is the
wrong one. They actually do catch lightning strikes, they
don't discharge the cloud to prevent them.

That sounds right.

I don't think anyone noticed, but a lot of the yagi could/would be
grounded. The mast would be, the support part could be, which means the
grounded part is more likely to be hit than the "hot" side. Like you say,
the lightning will go towards the easiest path, and that would be the
grounded part of the system.

That said, a near miss can be almost as fatal, and this does't completely
rule out a direct hit. YOu'd put lightning arrestors across the feedline.
In the early days, those were like spark plugs, a short distance for the
lightning to jump to ground. I'm not sure that really changed, but with
coax it got package up nicer. You also take precautions, put a neon bulb
across the receiver's antenna terminals, or now some solid state devie
that shrots to ground when a sufficiently high voltage hits, yet which
doesn't cause problems to reception otherwise.

If the antenna isn't being used, don't let the feedline in the house,
short it to ground outside.

Michael

 

[Bob Masta]

Actually I just recently read a piece about how lightning
rods work, and that one said that your explanation is the
wrong one. They actually do catch lightning strikes, they
don't discharge the cloud to prevent them.

Well, I expect a lot has changed since my '60s
Electromagnetic Fields EE classes. <g>

But how do they explain those teeny wires carrying all those
amps without exploding?

Best regards,


Bob Masta

DAQARTA v7.40
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusic generator
Science with your sound card!

 

[Tom Biasi]

Well, I expect a lot has changed since my '60s
Electromagnetic Fields EE classes. <g>

But how do they explain those teeny wires carrying all those
amps without exploding?

Best regards,


Bob Masta

Things haven't changed that much Bob. The wires are still not stronger
than an oak tree.

Tom

 

[Bill Gill]

Things haven't changed that much Bob. The wires are still not stronger
than an oak tree.

Tom

Well, maybe not, but when I visited George Washington's home
at Mt. Vernon the oak trees had lightning rods.

Bill

 

[Fred Abse]

Well, maybe not, but when I visited George Washington's home at Mt. Vernon
the oak trees had lightning rods.

Put there by Ben Franklin?

 

[Tom Biasi]

Well, maybe not, but when I visited George Washington's home
at Mt. Vernon the oak trees had lightning rods.

Bill

I'm pretty sure they don't want them hit.

 

[W. eWatson]

If there is no tall structure around, why the antenna is 15' high on the
roof? you dont gain anything (the sight angel may not change more than a
degree) lower it and let the pine tree get zapped.










--- news://freenews.netfront.net/ - complaints: [email protected] ---

I had the entire antenna system taken down about a week ago.