Auxiliary grounding electrode and light poles

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831

Senior Member
mshields said:
the practice can be deemed possibly helpful and in no way harmful.
I don't disagree w/ either of the above statements. Nevertheless, if we are to design all things helpful, owners will see an increase in the cost of building. If I design to be helpful as opposed to practical I increase costs and I also give the ECs and GCs something to poke at i.e. "my expensive systems".

I know it sounds petty, but I've lived on all sides of electrical work and it happens - a lot.

Rods @ poles based in theory and sound judgement - sure if it makes you feel good.

Rods @ poles JUST because you saw someone else do it - poor pratice IMO.
 

mshields

Senior Member
Location
Boston, MA
static build up

static build up

If it's true that a pole with bolts driven into a concrete base provide a signficantly lower impedance to ground than a rod, is not your argument relevant to static charge build up rendered void?
 

coulter

Senior Member
mshields said:
...Still, I can't see the connections within the concrete. I can certainly see the connection to a ground rod. ...
I don't think I understand your comment cause I'm pretty sure you already know this:

Concrete is hydroscopic (sp?) - absorbes water. It is fairly low resistance. Rebar and bolts in intamate contact with the concrete is fairly low contact resistance. A concrete ball in the ground has a large surface area and the concrete is always damp - fairly low contact resistance.

From the pole to the earth is fairly low resistance - the foundation is a vertical ufer.

Like I said, I'm pretty sure you already knew all this.

carl
 

mshields

Senior Member
Location
Boston, MA
ufer grounds

ufer grounds

I do understand that. But what I didn't know and what I'd be interested in from anyone who can provide it is empirical evidence that an Ufer ground consisting only of bolts into a concrete foundation without any rebar still provides a significantly better ground (lower impedance) than a ground rod.

If all you need is a bit steel into a concrete foundation for this amazing low impedance ground, why then does the code bother to define how much rebar and what size rebar you have to have interconnected in a footing or foundation in order for it to qualify as grounding electrode for a service?

I appreciate the input!!!

Mike
 

coulter

Senior Member
Ah - I see the issue. We have two different pictures of this pole foundation.

First I have not put in any light poles - but I have put in a few sign poles. The foundation consisted of a rebar cage 2 feet in diameter, 4 to 8 feet deep. The bolts were 1 inch, reaching down into the cage, 1 to 3 feet, tiewired or welded to the cage.

I suspect that is significantly different than the picture you had.

What I don't know is what is the norm for the non-specific light poles this post is discussing. Could be I am all wet about the extent of generic light pole foundation.

carl
 

dahualin

Senior Member
mshields said:
I do think the point about a base with rebar all properly interconnected, no doubt, provides a far better electrode (of the Ufer variety) than the ground rod is a good one. It probably renders the ground rod insignificant.



Mike

The purpose of ground rod is not to work as electrical grounding electrode for service as Ufer does, and is not to work as effective ground fault path for clearing ground fault as ground wire in site lighting circuit does. The purpose of the rod is for lightning protection only to discharge lightning energy. Why concrete base can not be lightning rod? I have read a research paper on lightning protection for power transmission tower. The concrete base has moisture inside. It will evaporate really quick and damage the base when it discharge lightning energy with huge amount current flow. So ground rod for light pole is necessary for lightning protection if it is located in such area.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Mike I will take a different approach on this subject as I have dealt with it on several data centers with a lot of parking lot light poles with security equipment.

Don't worry about driving any supplemental rods at the light poles. Just make sure you got a bond from the pole, to anchors, and the EGC and call it done.

The secret to keeping lightning out of the building is not at the pole. What I have had 100% success with is installing a branch panel that serves the paking lot on the outside wall where it goes out side. Stub up a piece of rebar (assuming new construction, otherwise make a GES connection) from a good ole fashion Herbert Ufer ground into the panel or just below it. Bond the the panel case and EGC bar. For the panel buy one with the best TVSS built into the panel you can afford protecting in ALL MODES (L-L, L-G, and N-G). Hope that helps.

Dereck
 
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coulter

Senior Member
dahualin said:
The purpose of ground rod is not to work as electrical grounding electrode for service as Ufer does, and is not to work as effective ground fault path for clearing ground fault as ground wire in site lighting circuit does. The purpose of the rod is for lightning protection only to discharge lightning energy. Why concrete base can not be lightning rod? I have read a research paper on lightning protection for power transmission tower. The concrete base has moisture inside. It will evaporate really quick and damage the base when it discharge lightning energy with huge amount current flow. So ground rod for light pole is necessary for lightning protection if it is located in such area.
David -
I probably read the same paper you did. The place I get stuck is why this ground rod is lower impedance than the concrete and steel. The answer I get is the high frequency lightning pulse prefers the rod - huh?? Well our testing support that premise. Can I see the test reports? Have never seen one yet. I'm not saying the lightning strike won't ruin the pole foundation, I'm saying I have never seen any peer reviewed tests that say a rod will save the foundation.

So far brian's comment was the best, "... If a site had 100 rods and never gets hit by lighting, all future sites will get 100 rods. ...'

If you have access to something besides anecdotal information, i'm interested in learning.

carl
 
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