small system grounding question

[icarus]

I have done a search, and haven't found a good answer, or at least one that is concise enough for me to under stand so I'll start a new thread.


We live on a small island in the middle (really the middle!) of a big lake on the Canadian shield. The entire island is almost bare rock, with little soil. The current grounding system(s) is this: Each generator frame, neutral ground, building ground etc carry a ground wire out the building, along the rock, and then into the lake.

In conversation with someone on another site, on another matter, it was suggested that this was a very dangerous situation. In the event of a strike in the lake,(a common event!) the energy could pass back up the ground wire and energize the system. We have never had any trouble in 60+ years of using this system.

My question is, is this system safe, or are there alternatives that I could explore. I cannot drive ground rods anywhere. My intuition is that any strike near enough to the ground wires (in the lake) would dissipate it's energy into the water so that the potential current would be very limited. I have had a ground wire struck once before. Lightning wrapped it's way down a tree, ran along the ground until it found the wire. It energized the system and blew out the charge controller as well as a 12vdc radio that was hard wired to the system. Other than that there was no damage.

I'm fairly confident that the gensets, and the inverters are safe (for protection from short circuit and shock) but the lightning question is now unclear. Any and all opinions would be appreciated.

Icarus

[Telco]

This was interesting. Did a little searching, came across two different possibilities for you to check.

One involves grounding in a rocky environment, which would require that you do some rock boring to get the grounds in.

The second one, which might better suit your needs, involves the grounding of ships at sea. From your description, being on a rock island in the middle of a lake essentially makes you like a ship at sea. The same grounding procedures used for a boat should work for your setup. This Yahoo search will provide more info.

Must be pretty cool living on your own island in a lake.

[niel]

there is a possibility of damage due to emp pickup and you have proven it can happen. on the other hand what else can you do without getting rediculous?
there may be one remote possibility though that could be worthwhile exploring. is there ground water below the house at all? you probably don't have a well due to the rock, but if you do then there is water below. anyway, contact with water below the house would be better than making a long wire run to the lake. the below ground water would most likely be in contact with the water in the lake and would help take away the possibility of emp pickup. the strikes on the lake do not hit the lake and run up to your house just so you know as that would be emp pickup on the exposed wire if anything did happen that way. in your blowout you just had the misfortune of the lightning travelling the way it did in its quest to reach a good ground. once it hit your wire the whole wire is energized.

[icarus]

This was interesting. Did a little searching, came across two different possibilities for you to check.

One involves grounding in a rocky environment, which would require that you do some rock boring to get the grounds in.

The second one, which might better suit your needs, involves the grounding of ships at sea. From your description, being on a rock island in the middle of a lake essentially makes you like a ship at sea. The same grounding procedures used for a boat should work for your setup. This Yahoo search will provide more info.

Must be pretty cool living on your own island in a lake.

From what I have been told, ships at sea have the advantage of being on salt water, and the salt water is MUCH more conductive than soft fresh water. I too have read that is what ships at sea count on. Question is, what do ships on the great lakes do?

Neil,

If I am reading you correctly, you would think that grounding into "wet ground" would be better than the lake directly?

What we have is exposed granite, with some areas covered with a thin layer of forest duff. Some areas are strewn with boulders, with the space between the boulders filled with 1000 years of duff, some times a meter or two above the bed rock. Near the lake shore, if you pull out a number of rocks, you can get to water. Would you suggest that would be a good ground spot?

There are a few (very few) spots where the bedrock is overlaid with a mix of sand, gravel, clay and big stones. I suspect if I tried to dig a pit by removing a bunch of rocks, I could lay a ground rod in the pit, then fill it again! Lotta work by hand!

Question is what is the relative safety of using the lake?

Tony

[niel]

i am not proposing you to break out a shovel, but do understand that water flows even through rocky terrain. if you do not have a well or already know there is water not far from the surface then it is not worth the big effort to dig to it or as i had in mind, drill to it. i know you mentioned your ground before, but refresh my memory on the distance to the lake and what you are using to run the ground to the lake with. also, if you have an idea of roughly how much higher than the lake your place is it could give me an idea on possibly how far a drill may have to go to get to water. in any case the extra you do may not be worth the extra return for your effort.
as to your present ground there is a risk, but unless you are in a faraday shield i think there is always a risk with any grounding system including one that may go under the ground as with ground rods. it has been shown in past studies that even an 8ft copper ground rod is insufficient, but that it is considered a minimum. my ground system is enormous compared to what most homeowners would do and there's still a chance it will fail or not be enough.

[icarus]

Neil,

I'm about 5' from the water both horizontally and vertically!

The current ground wire is a pair of #4 copper.

Drilling any kind of bore hole is impossible. We are 150kms from town, on a island that is only accessable by small boat, or over the ice in the winter.

I am going to try to upload a picture so you can get the idea. (I have never been able to up load pictures. I think I have figured out how to size them properly. (I am not very computer literate). The big rock in the foreground is bed rock.
The house itself sits on bedrock a foot or two below the surface.


Icarus

[niel]

hey i like your place. looks nice.
you are right there at the water and just be sure you have several feet minimumly into the water and more if you can, but i'd say that's the best that you can do. forget drilling or digging. as said before that no ground is foolproof, but yours is possibly better than most due to all of that water. that water does soak through rocks and makes streams through it and you couldn't make yourself such a sophisticated ground system if you tried. the key would be the contact area between your wire and the water as more contact does equate to a better ground connection.

[icarus]

Niel thanks (as always) for your advice,

The ground wire(s) go into lake for ~10'. (Now they are under 3' of ice,, will be 'till mid May!

I guess the short answer is that it has worked for 60+ years. A direct hit on the buildings would burn them to the ground probably, and a near strike will have it's way with the wiring. What is interesting is that we are really in the middle of the lake, the highest point for several miles. Over the years we have only taken a few strikes on the island itself. (That I know of!) One would think that we would be a lightning magnet, since we do get very wicked thunderstorms.

If anyone else as an opinion, I would love to hear it.

Tony

[Telco]

Have you considered putting a few poles that go higher than the house, say 30-40 feet to either side, in the water, with a grounding path on each? It would reduce the likelyhood of lightning actually finding the grounding on the house. Putting the poles in the water would make for a more direct path to the grounding source, and the power of the strike should dissipate radially from the point the pole meets the water so any backfeed that does hit the house ground should be a lot weaker.

The only thing I found was that shipboard lightning systems are grounded to a metal plate in the water, so if your wiring to the lake is just a loose wire you might attach a large metal plate to the end of it.

Hope all this helps.

[Ralph Day]

Tony,
Lovely looking palace you have there...but where are the panels? Are you maybe a beta testing site for Nanosolar...some kind of shingle, siding or fake pine needle thin film solar?

How close to the pilings has the lake ice been shoved up before? Must be one of those little worries rec property people have (i don't have those worries, sniff sniff sniffle).

Ralph