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Arthur Dent

Thu, Nov 27, 2014 12:42 AM

Here is a link to a good 12 page description of grounding
practices/requirements.

http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingRequirements_Reeve.pdf

Here is a link to a good 12 page description of grounding practices/requirements. http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingRequirements_Reeve.pdf

BH

Bill Hawkins

Fri, Nov 28, 2014 5:12 AM

Two of nature's great forces are hurricanes and thunderstorms.

A cloud with dimensions measured in miles can accumulate a great deal of
static charge during a storm, thousands of times more than any
human-built accumulator. When the volts/meter between the cloud and the
ground become high enough, lightning bores an ionized hole through the
air to some point on the ground. Occasionally the point on the ground is
a tall tree. Just up the road from here (MN, USA), lightning struck a
tall thick tree during a storm. The tree exploded from the pressure of
steam generated by electrical heating during the brief duration of the
strike. The trunk was split into four long parts, one of which landed on
the roof of the nearest house. That's quite a demonstration of energy.
Skin effect did not save the tree.

So I wonder about this concept of a lightning "arrestor". The report
referenced by Arthur Dent is quite complete. It also says, at the bottom
of page two, "It is impossible to prevent damage from a direct lightning
strike ..." Why, then, do people sell lightning arrestors when they
wouldn't dream of selling hurricane arrestors? Perhaps it is because we
create models of reality from our own experiences. Most of us have
controlled electricity in some way, so it ought to be a piece of cake to
arrest lightning. People who have witnessed the power of lightning have
a different model.

This business of grounding or Earthing suffers from differences in
scale. Human-generated electricity can be dissipated with ground rods if
the soil conditions are right. When lightning pumps hundreds of kiloamps
into the ground, the results can be measured in kilovolts per meter.
This is what electrocutes cows near struck trees, and why a golfer
should hunker down and keep his feet together when his hair rises.

You can rely on probability to avoid a direct hit, or you can erect tall
grounded masts around your tallest object. This proven method is used by
NASA to protect rockets on the launch pads. Each mast provides a cone of
protection with an angle of 45 to 60 degrees to the ground. See, for
example,

http://www.nasa.gov/mission_pages/constellation/ares/lc39b_lightning.htm
l

but you may need sand saturated with salt water for it to work.

Read the "Antenna System Grounding Requirements" and learn what you can
do to arrest the surges that accompany nearby strikes. The term "surge
arrestor" is much more accurate than "lightning arrestor".

Yours for safe time research,
Bill Hawkins

-----Original Message-----
From: Arthur Dent
Sent: Wednesday, November 26, 2014 6:42 PM
To: time-nuts@febo.com
Subject: [time-nuts] lightening protection of a GPSDO system / optical
isolated distribution amp

Here is a link to a good 12 page description of grounding
practices/requirements.

http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingR
equirements_Reeve.pdf

Two of nature's great forces are hurricanes and thunderstorms. A cloud with dimensions measured in miles can accumulate a great deal of static charge during a storm, thousands of times more than any human-built accumulator. When the volts/meter between the cloud and the ground become high enough, lightning bores an ionized hole through the air to some point on the ground. Occasionally the point on the ground is a tall tree. Just up the road from here (MN, USA), lightning struck a tall thick tree during a storm. The tree exploded from the pressure of steam generated by electrical heating during the brief duration of the strike. The trunk was split into four long parts, one of which landed on the roof of the nearest house. That's quite a demonstration of energy. Skin effect did not save the tree. So I wonder about this concept of a lightning "arrestor". The report referenced by Arthur Dent is quite complete. It also says, at the bottom of page two, "It is impossible to prevent damage from a direct lightning strike ..." Why, then, do people sell lightning arrestors when they wouldn't dream of selling hurricane arrestors? Perhaps it is because we create models of reality from our own experiences. Most of us have controlled electricity in some way, so it ought to be a piece of cake to arrest lightning. People who have witnessed the power of lightning have a different model. This business of grounding or Earthing suffers from differences in scale. Human-generated electricity can be dissipated with ground rods if the soil conditions are right. When lightning pumps hundreds of kiloamps into the ground, the results can be measured in kilovolts per meter. This is what electrocutes cows near struck trees, and why a golfer should hunker down and keep his feet together when his hair rises. You can rely on probability to avoid a direct hit, or you can erect tall grounded masts around your tallest object. This proven method is used by NASA to protect rockets on the launch pads. Each mast provides a cone of protection with an angle of 45 to 60 degrees to the ground. See, for example, http://www.nasa.gov/mission_pages/constellation/ares/lc39b_lightning.htm l - but you may need sand saturated with salt water for it to work. Read the "Antenna System Grounding Requirements" and learn what you can do to arrest the surges that accompany nearby strikes. The term "surge arrestor" is much more accurate than "lightning arrestor". Yours for safe time research, Bill Hawkins -----Original Message----- From: Arthur Dent Sent: Wednesday, November 26, 2014 6:42 PM To: time-nuts@febo.com Subject: [time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp Here is a link to a good 12 page description of grounding practices/requirements. http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingR equirements_Reeve.pdf

CA

Chris Albertson

Fri, Nov 28, 2014 5:26 PM

On Thu, Nov 27, 2014 at 9:12 PM, Bill Hawkins bill@iaxs.net wrote

So I wonder about this concept of a lightning "arrestor". The report
referenced by Arthur Dent is quite complete. It also says, at the bottom
of page two, "It is impossible to prevent damage from a direct lightning
strike ..." Why, then, do people sell lightning arrestors when they
wouldn't dream of selling hurricane arrestors?

Because the lightening arresters actually work. That is why they are sold
and wide used.

They do not and can not "stop" lightening. What they do is act as a
switch. They sense the voltage on a conductor. Normally the conductor is
allowed to have a signal voltage on it but if the voltage relative to
ground goes high the arrester closes a switch and connects the conductor to
ground. They don't stop lightening, they simply close to provide a path
to ground.

The tree could have been protected too. Let's say we could measure the
voltage at the top of the tree and if it ever got high we'd connect the top
of the tree to ground via a study copy cable. Then the current would have
avoided the tree trunk and flowed harmlessly to ground. What is amazing is
that we can build a simple switch that can work so fast. Many of them work
by using some kind of gas that is non-conductive until it becomes ionized
then the ionized gas connects the conductor to ground.

Also the arrester never sees the full current of the strike. In a coaxial
antenna cable MOST of the current is on the shield and this is shunted to
ground directly and never goes into the arrester.

And BTW we do build and use "hurricane arrestors". They are called storm
shelters. A large concrete structure works pretty much like a lightening
arrester, it deflects the effects of the storm from some small protected
area.

We should not argue that lightening protection is impossible because we
have many thousand of examples of them working. Yes normal variations and
statistics will eventually take out a system. But will it happen in your
lifetime?

OK one more analogy. Earthquakes. Why bother with robust building codes
when we know that a big enough quake will destroy any building? It's
because the "big one" is unlikely to occur during the building's lifetime
but we know 100% that many smaller ones will occur. So we protect for the
normal case

These things obviously DO WORK. There are cell towers all over the Orlando
Florida and they continue to operate. With a cell tower the FIRST line of
defense is structural grounding. The steel structure is bonded to a copper
grounding system. They get this down to about 6 ohms tower to ground and
most of the current follows that path. The second line is surge protectors
on ALL wires that come into the building.

Again you do NOT "stop" lightening with an arrester, you use them to
provide a easy path to ground..

Chris Albertson
Redondo Beach, California

On Thu, Nov 27, 2014 at 9:12 PM, Bill Hawkins <bill@iaxs.net> wrote > > > So I wonder about this concept of a lightning "arrestor". The report > referenced by Arthur Dent is quite complete. It also says, at the bottom > of page two, "It is impossible to prevent damage from a direct lightning > strike ..." Why, then, do people sell lightning arrestors when they > wouldn't dream of selling hurricane arrestors? Because the lightening arresters actually work. That is why they are sold and wide used. They do not and can not "stop" lightening. What they do is act as a switch. They sense the voltage on a conductor. Normally the conductor is allowed to have a signal voltage on it but if the voltage relative to ground goes high the arrester closes a switch and connects the conductor to ground. They don't stop lightening, they simply close to provide a path to ground. The tree could have been protected too. Let's say we could measure the voltage at the top of the tree and if it ever got high we'd connect the top of the tree to ground via a study copy cable. Then the current would have avoided the tree trunk and flowed harmlessly to ground. What is amazing is that we can build a simple switch that can work so fast. Many of them work by using some kind of gas that is non-conductive until it becomes ionized then the ionized gas connects the conductor to ground. Also the arrester never sees the full current of the strike. In a coaxial antenna cable MOST of the current is on the shield and this is shunted to ground directly and never goes into the arrester. And BTW we do build and use "hurricane arrestors". They are called storm shelters. A large concrete structure works pretty much like a lightening arrester, it deflects the effects of the storm from some small protected area. We should not argue that lightening protection is impossible because we have many thousand of examples of them working. Yes normal variations and statistics will eventually take out a system. But will it happen in your lifetime? OK one more analogy. Earthquakes. Why bother with robust building codes when we know that a big enough quake will destroy any building? It's because the "big one" is unlikely to occur during the building's lifetime but we know 100% that many smaller ones will occur. So we protect for the normal case These things obviously DO WORK. There are cell towers all over the Orlando Florida and they continue to operate. With a cell tower the FIRST line of defense is structural grounding. The steel structure is bonded to a copper grounding system. They get this down to about 6 ohms tower to ground and most of the current follows that path. The second line is surge protectors on ALL wires that come into the building. Again you do NOT "stop" lightening with an arrester, you use them to provide a easy path to ground.. -- Chris Albertson Redondo Beach, California

BC

Bob Camp

Fri, Nov 28, 2014 5:57 PM

Hi

Any form of protection (no matter what you are protecting against) is part of a system. The more complex the system, the more it costs and the larger it gets. The more details you cover in your system the more 9’s you get to put in the “99.9xxx% protection” statement. Is there an event out there that will be the 0.001% event - sure. Are we talking about lightning or redundant timing systems? - it really does not matter. The same principle applies to both. Are two GPSDO’s enough? Would adding a couple of Cs standards make it better? You are just adding more 9’s to the number. Put a structure over your house that looks like the one over your local power switching station and you add a few more 9’s on the lightning protection number. Same idea as adding a few Cs standards to your system.

In both examples, the added gear will only add 9’s if it’s part of a properly designed system. Simply adding more of XXXX isn’t likely to help much compared to a careful design. People make timing setups that run pretty much forever and ever. A mountain top (or skyscraper top) communications setup can be designed to take multiple direct lightning hits an hour and keep right on going and do it for may years. There are lots of systems out there like that. All of it just takes a careful approach with good attention to the details. Yes there is the minor issue of having enough cash on hand to pay for what’s required ...

Bob

On Nov 28, 2014, at 11:26 AM, Chris Albertson albertson.chris@gmail.com wrote: