Lightening - ground currents

[Gerald Sargent]

Few realise that cables buried in the ground to outside observatories can result in severely
damaged equipment due to spikes induced by ground currents from lightening strikes as
much as a mile or so away. Computers, CCD Cameras, modems, motors for roll off roofs,
and many other devices can severely damaged, usually terminally.
One should use a "surge protector" at the observatory end, and ensure that a good ground
stake is attached to the third "earthing" conductor of their input to the surge protector.
I might add that indeed few electricians know anything about ground currents.

[mill (Martin)]

OOOOOHHHHHH!!! I think most electricians know about ground currents and i am one of them.
Ground currents are mostly low after 20Mtr depending on the moist in the soil.
As you know, current will follow the path of least resistance and will not go into a insulated cable.
Good practice is as always to unplug any equipment from the power point when there is a thunder storm.

PS: if you put another earth stake at the obs power you might induce a ground loop.

[duncan]

Very good point made Gerald. Just had a quick look on the web and came up with this. Read the paragraph under "Ground Currents"

http://www.feb.se/EMFguru/EMF/ground-currents.html

Cheers

[Hagar (Doug)]

Hi Gerald, I am a qualified electrician with an engineering degree to boot and am quite aware of Ground currents and the dangers they impart on Astro and computer equipment but to add another earth stake is opening the door to a very dangerous situation. In the event of requiring an earth stake at your observatory you really should disconnect the earth which is in the cable leading out to the observatory and turn the observatory into a seperate MEN system (Multiple earthed neutral). You will also require a switchboard to provide the protection of your observatory cabling. By far the best way to protect any electrical or electronic equipment, be it in your observatory or your house during an electrical storm is to physically disconnect it fron all sources of supply and earth by unplugging it.
Much of the commercial surge protection equipment sold is only good for minor transient rises in voltage and provides little protection from a very close lightning strike or one on the local reticulation grid.
Please be careful adding extra earth stakes to your electrical installation without the advice of a qualified electrical contractor.

[Gerald Sargent]

I wrote my warning because I have several times suffered from the effect of lightening strikes at some distance, certainly more than a kilometer. My worst case took out a
computer, modem and router, I now use a correctly instally surge protector.
I also had some years ago when a I used a 4ft disk on the roof on and AZ-EL
computer controlled tracking systenm to track weather satellites. Here distant
lightening strikes induced currents in the coaxial out running from the low noise
giga-hertz amplifier at the centre of the dish to the main receiver in the house, this cable carried rf down and 12v dc up to the amplifier. The currents induced in the outer caused transient spikes on the inner that blew up the fet amplifier in the LNA. I cured this by the
proper use of faraday shields, and voltage regulators. So to say 20 meterrs as a limit for
ground currents of consequence did not apply inb any of these instances.

[stephenb (Stephen)]

All sound advice from an expert in the know , thanks Doug.

I don't have an observatory, but we always unplug the more sensitive items leading up to thunderstorms - LCD TV, DVD, computers etc. It's a habit that should be second nature to everyone. There is no harm once the plug is out of the wall.


I wonder how many observatories out there have not had correct, legal wiring done on them?

[allan gould]

I thought long and hard about power to my new observatory and reLised that with all the lightning strikes I've seen here in Brisbane that I would NOT put underground power in but instead run an extension cord to it. AgIn thanks for tour timely advice Gerald - it's much appreciated.

[westom]

Originally Posted by Gerald Sargent

Few realise that cables buried in the ground to outside observatories can result in severely

Originally Posted by Gerald Sargent

damaged equipment due to spikes induced by ground currents from lightening strikes as much as a mile or so away. Computers, CCD Cameras, modems, motors for roll off roofs, and many other devices can severely damaged, usually terminally.

I confirm what Gerald has posted with many technical reasons why and decades of experience. Appreciate that most electricians do not understand this. Experience is often found in amateur radio operators, rocket launch facilities, munitions dumps, commercial broadcasting stations, farmers, Telstra switching stations, and in science publications even 100 years ago.

An application note from one professional demonstrates two structures. Each must have its own single point earth ground. Any wire in every cable that enters either structure (overhead or underground) must first connect to that single point ground.:
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

To make both single point grounds better, an interconnecting buried wire connects to both.

Both underground and overhead wires require the same protection as that app note demonstrates.

For example, any cable TV wire must connect short (ie 'less than 3 meters') to single point earth ground before entering the facility. Other wires (AC electric, telephone, ethernet) cannot connect directly. That is the only purpose of an effective protector. Make that same short connection to earth.

No protector is protection. So many educated only by myths will have difficulty. So it is repeated. Protection is not provided by any protector. The protector is only a connecting device. Either it is effective due to that short connection to single point ground. Or it may even contribute to damage of adjacent and powered off electronics.

Replace that antenna in the app note with an observatory. To perform proper earthing, the electrician must take special precautions to also conform to what electricians are taught - human safety requirements.

Disconnecting has a long history of failure. Even early 20th Century ham radio operators would disconnect their antennas. Put the antenna lead inside a mason jar. And still suffer damage. Damage stopped only when the antenna was earthed.

What is the only thing that provides surge protection? Well, what is surge protection? Protection is only and always about where energy dissipates. Either energy dissipates harmlessly in earth. Or dissipates destructively in nearby (even powered off) appliances. Protection is always about keeping surge energy outside the home or observatory.

Farmers can confirm what Gerald has posted. 15 meters from a cow is a tree struck by lightning. Therefore the cow is killed. Why? Surge protection is always about following the current. The current from a cloud three kilometers overhead must connect to charges four kilometers distant. The shortest path is not five km across the sky. Shortest electrical path is 3 km down to the tree, then four km through earth. The shortest path is also up the cow's hind legs and down it fore legs. Another concept rarely understood by electricians because the codes do not discuss it.

That cow suffered a direct lightning strike because it did not have 'single point' grounding. Had a buried copper wire surrounded the cow, then currents would have flowed through the wire; not through the cow. And yes, ground currents from nearby lightning strikes can be that massive; are really a direct lightning strike.

This famer's example is also why the term 'single point earth ground' is repeatedly used. And why Gerald's post so accurately demonstrates what was well understood even 100 years ago.

If building an observatory, then surge protection starts before footings are poured. Learn about Ufer grounds that were originally developed so that direct lightning strikes to munitions dumps cause no damage - no explosion. And yes, concrete is an electrical conductor.

Protection is always about where energy dissipates. No plug-in protector provides protection. Will not claim protection. Cannot dissipate a typically destructive surge. Is a ‘profit center’ because so many foolishly spend tens or 100 times more money on those ineffective devices.

The informed spend so much less money, upgrade earthing, and install a 'whole house' protector from more responsible companies (ie Clipsal). The informed learn why grounding for transistor safety must exceed what electricians install only for human safety.

Surge (lightning) damage is directly traceable to human failure. Effective protection has been well understood for over 100 years. A protector is only as effective as its earth ground.

[Gerald Sargent]

As I started this thread I had better make a correction. My attrention has been drawn to
the possibility that some of my suggestions may contravene regulations and put
insurance at risk. It is suggested therefore that anyone with concern about lightening
and associated ground currents get advice from a licenced electrician with experience
in this matter

[westom]

Originally Posted by Gerald Sargent

It is suggested therefore that anyone with concern about lightening and associated ground currents get advice from a licenced electrician with experience in this matter

As posted earlier:

To perform proper earthing, the electrician must take special precautions to also conform to what electricians are taught - human safety requirements.

Surge protection is always about both meeting and then exceeding code requirements for earth ground. Earth ground which is different from the safety ground found in wall receptacles.

For example, if the wire to ground has a ninty degree bend, then that wire meets safety codes and compromises surge protection. An example of how earthing can meet code and still not be sufficient for transistor safety.

[Hagar (Doug)]

Westoms post makes one very relevant statement. That is "Protection is always about where energy dissipates. No plug-in protector provides protection. Will not claim protection. Cannot dissipate a typically destructive surge. Is a ‘profit center’ because so many foolishly spend tens or 100 times more money on those ineffective devices."

To follow a considered safe installation as detailed by the company listed above would add thousands of dollars to the cost of an observatory installation. This may be appropriate for a commercial installation it is overkill for a domestic installation. In most cases a good serge protector provides some protection but the best and cheapest method is just to pull the plug.. Physical isolation is the only proven method of eradicating surge or ground current risks. House contents insurance should cover the rest of the risk.

[jjjnettie (Jeanette)]

Originally Posted by Hagar

No plug-in protector provides protection. Will not claim protection. Cannot dissipate a typically destructive surge. Is a ‘profit center’ because so many foolishly spend tens or 100 times more money on those ineffective devices."

[/FONT][/COLOR]

The Belkin range of surge protectors come with insurance to cover this.
Though that doesn't make up for loss of data.

[westom]

Originally Posted by Hagar

To follow a considered safe installation as detailed by the company listed above would add thousands of dollars to the cost of an observatory installation.

More expensive solution is that Belkin protector. Serious and significant protection is routine with one 'whole house' protector and a $10 ground rod. To make their protection a little better, high reliability facilities spend massively on extensive grounding. Because that earth ground determines protection.

Costs approach zero if protection is installed when footing are poured.

For homes, one 'whole house' protector costs about $1 per protected appliance. How much per appliance for that Belkin with its mythical warranty? That Belkin has all but no earthing. It does not even claim protection in its numeric specs. Its warranty is so full of exemptions as to not be honored.

How to identify least effective protector? One characteristic: it has a big buck warranty. We all learn this from free markets. Since GM has a clearly superior warranty, then GM products are superior to Honda? Nonsense. Because GM's hyped warranty is so much better, then we can predict from free market history that GM products are the least reliable.

Why do high reliability facilities use 'whole house' protectors? Because that solution is effective. And may cost tens or 100 times less money per protected appliance.

More expensive and least reliable solutions are plug-in protectors such as that Belkin that does not even claim to provide effective protection in manufacturer's numeric specs. Listed in the previous post is a less expensive and clearly superior solution. The only solution implemented in facilities that must never suffer damage.

[GTB_an_Owl (Geoff)]

so where does an UPS solution stand in all this ?

geoff

[PeterM]

Interesting thread,

I go with Hagar totally and unplug the power from the wall and also from the scope and ccd camera whenever there is a storm around. Yes I have the Belkin protector also but I reckon a claim would be like pushing the proverbial up hill.
However, noting that concrete is a conductor what does this mean for my steel pier, dynabolted to a 3x3m x100mm slab, that carries the LX200 on top, say given a close (and how close) ground strike? Even though the power is unplugged at the wall and at the scope & CCD are my electronics still at risk? If so how else do you guard against this, other than SPECIFYING my equipment - (this is a VERY important word - it is such a get outline for insurers - "oh you don't have it specified") in my contents insurance policy.
Oh and by the way make sure you have told them the equipment is housed outside the house and send them an email confirming same.
PeterM.

[Ric]

A very interesting and informative thread.

I have what may be a dumb question. When I get around to building my observatory I intend to run it on solar power thus doing away with the need to have any cabling in the ground.

Would ground currents have any effect on solar powered items?

[westom]

Originally Posted by GTB_an_Owl

so where does an UPS solution stand in all this ?

The only UPS that really claims or provides protection is a building wide system that is located within meters of single point earth ground. Every plug-in UPS claims near zero protection. Since they forget to put numbers in a sales brochure, most automatically assume 100% protection.

Most UPSes connection electronics directly to AC mains. How does that relay stop what three kilometers of sky could not? It doesn't. Either a surge connects to earth before entering the building. Or it is inside the building hunting for earth destructively via electronics.

Ben Franklin demonstrates the concept in 1752. Lightning found earth ground destructively via wooden church steeples. To have not damage, Franklin made no effort to stop or block the surge. Franklin simply gave lightning a better path to earth. The lightning rod is not protection. The lightning rod simply connected lightning to protection - earth ground. Now energy dissipates harmlessly in earth; no in wood.

Protection is always about diverting that current. Always. Anything that would stop, block, or absorb a surge is also called a scam. You do not stop what 3 kilometers of sky could not.

[westom]

Originally Posted by Ric

...I intend to run it on solar power thus doing away with the need to have any cabling in the ground.

Originally Posted by Ric

Would ground currents have any effect on solar powered items?

Ground currents are the same problem cited in that cow. First, you want no currents entering and leaving the solar array. If the array is surrounded by a buried ground ring, then voltages everywhere in that solar array are same - no current.

BTW, this is what farmers do to eliminate ground currents in a barn. Ground currents can cause a significant reduction of milk production from cows. Not just currents from lightning. Also stray currents from nearby AC distribution lines.

That previous example showed two structures - a building and an antenna. If the solar array is not part of the building, then the solar array must be treated as a second structure - just like the antenna in that application note.
http://www.erico.com/public/library/fep/technotes/tncr002.pdf

Two factors to remember. First, conductivity and equipotential are both made as best as possible so that no currents flow through the cow, building, or structure.

Second, resistance is not relevant. Conductivity is about low impedance. Wire resistance is defined mostly by wire diameter. Wire impedance is mostly defined by wire length and other factors (ie sharp wire bends). Surge protection is always about impedance. Impedance connects as low as possible to earth ground. Impedance between protectors and electronics higher. Impedance - not resistance - determines where surge currents flow.

[PeterM]

Hi Westom,

Thanks for your contribution very informative, I think I am reading that my steel pier bolted to the concrete (as noted above) even with everything unplugged, carrying the 'scope and electronics, is still at risk is that right?
PeterM.

[tlgerdes (Trevor)]

Remember that it is not only power cables, but any cable ie USB, serial, ethernet etc

North Sydney library found this out 15years ago, when a strike hit the parking lot 50 metres away and blew out the serial ports of 43 terminals. Smelt shocking