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Grounding a megtree pole question


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Not sure if the right place, but he it goes. I have approx. 28 feet of Rigid conduit pipe sticking up in the air. We don't get a lot of lighting, but it could happen. I have a 4 foot ground rod that I pounded into the ground about 25 feet away from the tree and any building. What would be the correct size of wire to run from pole to ground rod?

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Would someone please explain to me and TJMarty why you need to ground a metal pole that's in the ground? Seriously. :confused:

Your not making a direct contact with the earth, it is insulated by the PVC and the bottom of the hole is cement. Now go back to hanging lights LOL.

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Vroach,

Can you wrap your mind around the concept of a few mA versus the energy that is in a lighting bolt?

At first I was like what the heck, till I heard it is in PVC and concrete, that changes everything.

bdeditch, I'll compromise and say that #4 stranded will do. Actually I have seen that something like copper flashing but a little thicker is suppose to be superior to a round wire. Also in a case like this when using stranded, pick a larger size versus solid wire.

Oh and your ground rod is way to short. Thats why they sell them in 10' lengths. And if you are going to be this worried about lightening. Are you doing anything else like gas tube or MOV from each lead coming into the controller box? I am speaking of both hot and neutral.

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You are thinking lightning, but the other concern is a short in your Xmas lights. Any grounding would likely only help in the event of a short. If you have GFCI this is not as much of a concern.

Typical ground rod is 5/8 8' copper clad rod.

I don't know that any type of grounding the average DIYer would install would provide any type of protection for lightning.

Grounding for lightning rods is typically (3) 5/8x8' rods in a triangle about 6' apart. They are joined with a braided copper wire, not sure what size it is, but it's big. Bigger than #2.

In any event you would still have inductive current and EM to deal with. If you had a direct strike on your pole the EM would probably fry any controllers you had in the immediate area.

I'm by no means an expert on the subject, but I believe I am correct.

Tim

Edited by Mr.Tim
ground rod size
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Ok I forgot to mention the 3 3 1/2 foot metal tie down stakes that are also connected to the guide lines. These are screwed into the ground and then about 2 1/2 feet of cement on top of them. getting an 8 foot rod in the gound here is a hit and miss project. We are in the foothills of the Sierra Nevada's.

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Thanks Mr. Tim,

You corrected a few facts for me. Yes I now remember after you stated so that the rods really are 5/8 X 8' long. And yes 3 rods are better than one.

I worked at a plant that made missles and installed 550lb H.E. warheads. The part of the plant that had the warheads was in a building that had 120' tall lighting rods around the building. There was a network of bare cables from pole to pole with ground rods every so often. Then this ring had spokes that went out for a bit, 50 or 100' to a second ring with more ground rods along this 2nd ring. I maintained the fire alarm system. One time I found the switch in a pull station blown away after a rather nasty electric storm. But the circuit board that this was attached to was fine. It had gas discharge tubes attached to the two wire coming in from the remote pull station. The other side of the gas discharge tube is connected to ground. Any voltage over what the GDT is rated for causes the tube to conduct to ground shunting away harmful voltages to the circuits.

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Thanks Mr. Tim,

You corrected a few facts for me. Yes I now remember after you stated so that the rods really are 5/8 X 8' long. And yes 3 rods are better than one.

<snip>

Well, that's the standard around here anyway. I do believe they come in 10' as well but are not common.

Most lightning protection is engineered so who knows what the exact requirements are.

My opinion is that installing the grounding to try and dissipate a lightning strike is probably not a good investment of time or money.

Grounding the pole in the event there is a short in the lights, well that makes sense.

I would use a 5/8x8 rod and whatever wire I had around. Bare or insulated, solid or stranded, doesn't make much of a difference. If you are using #6 or smaller it should be bare or green. Larger than #6 it can be any color but you should reidentify it with green tape.

Then again we all bend the NEC a teeny tiny bit anyway, so just having any sort of grounding conductor is a plus :)

Tim

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