Off grid grounding technique?

Re: Off grid grounding technique?

Have you been "hit" by lightning in your knowledge?

Just "sinking" some 10's of feet of wire (as much as you wish to $pend) into the lake bottom muck will probably be as good as it gets... The lake itself is probably not very conductive.

That is why people are warned to get of of lakes/pools during a thunderstorm. The human body (with all of the salt/ions/water) is relatively very conductive--so the any and all current "in the area" will try and go straight through the body (finding "ground").

Given that you are near the water's edge--your location probably has a much better chance of attracting a strike than the nearby lake would (increases the odds of your home/area being hit).

There are probably several effects of atmospheric electricity..

The first is the normal charge of 100 to several hundred volts per meter (which can exceed 10,000's of volts per meter pre-strike). Metal objects (particularly tall objects) being grounded to earth (does not take a low resistance connection). This prevents a person from walking up to a tower from getting shocked (pretty nasty one because large tower has lots of capacitance). As HAMs know--even an antenna on a tower can pick up a charge if the cable is left open at ground level.

Here is a good point of discussion... There are several things that attract lightning... Sharp Points and Voltage differential. Sharp points are great (or at least) for lightning rods to attract lightning within a few 10's of feet to hit it, instead of something nearby (and cause damage/start fire). The other is grounding a tower/object increases the electric potential to attract a lightning strike...

So any grounding can attract lightning, and physical metal objects do to...

Now that you have put up your lightning attractor--it seems like a good idea to safely route the energy via braid copper cable from the lighting rod / metal structure to earth.

I will leave it to professionals to better describe the requirements for a Lightning Protection System. From page 2 of their little FAQ:

[FONT=Arial, Helvetica, sans-serif]Who Needs Lightning Protection?[/FONT]

[FONT=Arial, Helvetica, sans-serif]Lightning can strike anywhere and do millions of dollars worth of damage. Lightning is to blame for more deaths and property loss than tornadoes, hurricanes, and floods combined. And although we cannot yet predict where lightning will strike, there are some factors that increase the risk of a lightning strike. If your home or business meets 5 or more of the following criteria, you are in a high risk group. [/FONT]

• [FONT=Arial, Helvetica, sans-serif]has had previous lightning damage[/FONT]
• [FONT=Arial, Helvetica, sans-serif] is located in an isolated, open area[/FONT]
• [FONT=Arial, Helvetica, sans-serif]is located on a hill[/FONT]
• [FONT=Arial, Helvetica, sans-serif]located near a large body of water [/FONT]
• [FONT=Arial, Helvetica, sans-serif]is located in an area that has a high number of thunderstorms [/FONT]
• [FONT=Arial, Helvetica, sans-serif] has tall trees overhanging the roof [/FONT]
• [FONT=Arial, Helvetica, sans-serif]has metal, brick or stone chimney brick [/FONT]
• [FONT=Arial, Helvetica, sans-serif]has metal ridge vent [/FONT]
• [FONT=Arial, Helvetica, sans-serif]has aluminum siding [/FONT]
• [FONT=Arial, Helvetica, sans-serif]has no surge protection [/FONT]

My two cents--If you do not install a lightning protection system--almost anything else you do is not going to help much (grounding structures, towers, arrays, etc. Routing the Lightning System cable away from any other cables/wiring/sensitive electronics will be a big help (prevent capacitive and inductive coupling from LS to other stuff).

However, there is the counter argument (as I understand it) if you do nothing to overtly attract the lighting--it will as likely find somewhere else to strike and if you keep your equipment separate from the "earth" then nearby strikes will not create potential across your equipment (i.e., two points in the ground 50' apart may have hundreds or thousands of volts of differential potential from a nearby strike). Creating a single ground point to reference all "in-house" and "around house" electrical equipment will help reduce the issue of ground potential.

If I recall correctly, Solar Guppy (who is in Lightning Central) -- believes in isolation (disconnecting arrays from building/inverters/charge controllers) and avoiding grounding of his solar arrays and their aluminum frames. Both reduces the changes of a strike--and limits the possibility of a nearby strike of coupling into his equipment. And it seems to work for him (not trying to put words in SG's posts--search around for his other posts that describe what he recommends and his results--no damage, as I recall--Not quite sure that I believe that his practices are as "untrained human" safe as heavy ground would be; and no human should be out and about in a lightning storm anyway--But they seem to work for him).

Remember, lightning contains both high currents and high frequency--so following good RF practices (as well as lots of copper/aluminum) helps.

-Bill

Re: Off grid grounding technique?

icarus wrote: »

I heard once, and have no recollection of where, the real way that lightning work is that they provide such a good path to ground that they (can) dissipate enough static energy such that a lightning strike doesn't happen. In the event that it does strike, the rods and the ground wires then can direct the strike off the to reduce or eliminate damage.

Does not make sense to me--but I will not claim to be an expert in the field... I go with -- anything that makes conduction easier will draw a strike (sharp points, ionized air such as a radionuclide on the tip of a rod, something conductive that is at a greater potential difference with respect to the source of the lightning, etc.).

From what I have read about items that are intended to reduce the "field" in an area (ball of spikes?) to dissipate lightning before it strikes, they do not work; Charge Transfer System:

Charge Transfer System is Wishful Thinking, Not Science

New Mexico Institute of Mining and Technology, Socorro, NM 87801
Langmuir Laboratory for Atmospheric Research

November 24, 2000

Jodi Haasz
Standards Board
Standards Activities
IEEE- Power Engineering Society
...
Piscataway, NJ 1331-1331

Subject: Project Number P1576 (Proposed Standard for Lightning Protection System Using the "Charge Transfer System" for Industrial and Commercial Installations.)

Dear Administrator Haasz:

The purpose of this communication is to recommend that the IEEE be extraordinarily careful in its consideration of the proposed standard. Before a standard for the use of "Charge Transfer Systems" is issued, the Standards Board members should obtain and assess information on the electrical responses by these devices under active thunderstorms that has been measured by competent, independent investigators.

The present consensus held by members of the lightning and thunderstorm electricity community in both the American Geophysical Union and in the American Meteorological Society about these devices is that they are replays of Benjamin Franklin's original, failed ideas about lightning rods. In the course of some parlor experiments, he and his associates discovered that they could discharge electrified objects silently, without sparks, by approaching them while holding a sharp-tipped needle directed at the object. This discovery of the "point discharge" or "corona current" phenomenon led Franklin to suggest that, perhaps, thunderclouds could similarly be discharged, thus preventing lightning, by taking away its electricity. However, after Franklin erected a sharp-tipped iron rod for this purpose, instead of discharging a thundercloud passing above, his rod was struck by lightning. Thereafter, Franklin recognized that a primary function for an elevated rod was to be a lightning receptor and to carry the lightning to Earth, around structures that were to be protected.

Despite this new and unexpected function that his rods appeared to serve, Franklin (1767) remained enamored of the "power of a point" and recommended that the tips of lightning rods be sharp, a configuration that is still widely used today although the virtue of having sharp tips on lightning rods has never been established. Our assessment of the experience gained since Franklin's time is that sharp rods and "dissipation arrays" exposed in isolation on high towers are often struck by lightning but there is no credible evidence that they prevent lightning, which usually initiates high up in thunderclouds...

Back to Tony:

I suspect that I am stuck between a rock and a hard place on this. (no pun intended!) By providing a good path to ground, my chances of getting struck are greater, but if I do I will be somewhat protected. Heads you win/tails I lose.

I suspect you are correct.

To answer our first Question Bill, we have been struck pretty close to the buildings over the years, usually striking a tall tree, working it's way down the tree, often jumping to another, and then into the duff. One time it found a #4 copper wire that was wired to a Charge controller and battery bank. It was 100' away, and it toasted the CC, a couple of 12v radios and nothing else. Lucky I guess.

Less lucky and more a standard operating procedure?

For DC circuits--I wonder that any lightning suppressor is ever going to be fast enough and work at a low enough voltage to protect anything. If a Lightning Suppressor is installed--my suggestion would be to always install "pairs"--For example, install one on the + lead and the - lead. That way, ideally, both would fire at the same time and prevent on terminal from attaining a different voltage vs the other (engineering speak, prevent a common mode current/voltage spike from turning into a differential mode spike which will toast the input circuitry--most circuits can withstand common mode energy injection better than differential mode injection).

Which would lead to another protection device... Basically wrap a couple turns of cable around a loop of steel, ferrite, copper conductive band, etc. Basically you make a common mode Choke to prevent common mode lighting energy from entering your equipment (this is commonly done to reduce RFI emission and susceptibility for FCC/CE compliance--should help with lightning--maybe--depends on the energy levels--and RFI was typically a concern >30 MHz--protecting against 10kHz or less is something I would have to think about to design a "proper" common mode choke--I.e., more Googling --but not tonight ).

I do think the steel roof will add a level of protection assuming it is grounded.

Not really. Steel is a poor conductor... Joints are not made to be electrically secured, still need way to "capture" the energy and move it safely off the building.

More on roofs (including metal) Specifications for Lightning Protection ASAE Engineering Practice (PDF Download)

Metal roofing and siding, eave troughs, downspouts and other metal parts are not acceptable as substitutes for lightning conductors. A lightning conductor system shall be applied to the metal siding of a metal-clad building in like manner as on buildings without such metal coverings.

Down conductors, which are continuations of roof conductors, shall be as widely separated as possible at diagonal corners of rectangular buildings, and diametrically opposite on cylindrical structures.

Treating a metal roof like a conductor where the A/C (high frequency current) flows at the outside or skin of the wire (and why a proper lightning control cable is braided fine wires instead of a chunk of #4 copper)--the skin depth of lightning:

Most lightning current energy is below 10 kHz. While there is some energy at 100 kHz, very little remains above 1 MHz. In this case, the design point for frequency might be at least 10 kHz, which means that conductors over 0.052" (1.3 mm) thick (representing a skin depth of 0.026" (0.66 mm) on each side of the conductor) have reduced conducting efficiency.
...
The skin-depth effect means that copper straps about 1/16" (1 mm) thick will tend to outperform round wire of the same cross-sectional area, since the full cross section of the strap will conduct high current. Admittedly, wire (particularly stranded wire) is much easier to install, join, and change direction than straps. Flat-braid cable is a good alternative for vibration resistant and highly efficient grounding, which is why it is commonly used in aircraft-grounding applications.
...
The length of the cable increases the impedance dramatically. Larger-diameter cables have slightly less impedance, due to the larger surface area. The benefit of larger diameter is less significant for resistive impedance, due to the skin-depth effects.

So... The last clip would indicate that running 100' of #4 copper solid wire (just a SWAG) underground/underwater is of limited use... The "voltage drop" due to A/C impedance (DC Resistance is not the limiting issue) means that little energy will be carried those hundreds of feet out to the lake... Perhaps, given other specs. that say earth ground rods should be within 6' of each other would indicate that 6' or less is good, and 60' or longer is approaching useless for power dissipation (using a typical engineering design rule of thumb--difference of less than 2x are virtually the same; whereas differences of 10x an greater can be ignored--in this case a 10x longer wire (60+ foot) will hardly dissipate more energy than a 6' wire--again lots of SWAGing going here--but gives a few more points to research).

I don't know--just lots of random thoughts going on here on what makes sense to my personal knowledge.

-Bill

Note: SWAG -> Scientific Wild Ass Guess :roll: