Ground Rods at Light Poles

[bwat]

And even if we were to concede that a ground rod is somehow establishing a better connection to the earth around it than the concrete and rebar was doing, I think it's reasonable to make the argument that the ground rod is possibly doing more damage than good regarding lightning. One could claim that the pole is now more attractive to lightning and is then more likely to be struck.

 

[Rock86]

That article basically does not have anything to do with grounding electrodes as asked about in the OP.

Did you read the article? I pretty clearly discusses points relating to the topic of discussion.
" Auxiliary grounding electrodes are permitted byNEC250.54, but this section makes it clear that the electrode must be bonded to the EGC, and the earth shall not be used as an effective path for ground-fault current. " - that is straight out of the article.

 

[kwired]

Did you read the article? I pretty clearly discusses points relating to the topic of discussion.
" Auxiliary grounding electrodes are permitted byNEC250.54, but this section makes it clear that the electrode must be bonded to the EGC, and the earth shall not be used as an effective path for ground-fault current. " - that is straight out of the article.

The whole point of the article is about the importance of having an equipment grounding conductor, this thread is about whether a grounding electrode at light poles is even necessary.

 

[jaggedben]

Did you read the article? I pretty clearly discusses points relating to the topic of discussion.
" Auxiliary grounding electrodes are permitted byNEC250.54, but this section makes it clear that the electrode must be bonded to the EGC, and the earth shall not be used as an effective path for ground-fault current. " - that is straight out of the article.

The OP made clear he understands this, and was asking if electrodes help with lightning or not. It's a good article but it doesn't address the lightning topic.

 

[jaggedben]

And even if we were to concede that a ground rod is somehow establishing a better connection to the earth around it than the concrete and rebar was doing, I think it's reasonable to make the argument that the ground rod is possibly doing more damage than good regarding lightning. One could claim that the pole is now more attractive to lightning and is then more likely to be struck.

Granted I'm not a physicist or a lightning protection expert, but I believe this is incorrect. Lightning tends to strike tall objects because it takes the shortest path through the air, which has the most resistance. The differences in resistance among a street pole or a tree are negligible compared to the air resistance, and therefore have little to no effect. The build up in potential happens between the tip of the object and the thundercloud above, regardless of the material of the object.

Put another way, if metal objects were that much more likely to be struck by lightning, no one would ever build metal barns on the Midwestern plains. But they do and it's not a problem.

This is to be distinguished from how the different materials matter once lightning has decided to strike that object or a location nearby.

 

[kwired]

Granted I'm not a physicist or a lightning protection expert, but I believe this is incorrect. Lightning tends to strike tall objects because it takes the shortest path through the air, which has the most resistance. The differences in resistance among a street pole or a tree are negligible compared to the air resistance, and therefore have little to no effect. The build up in potential happens between the tip of the object and the thundercloud above, regardless of the material of the object.

Put another way, if metal objects were that much more likely to be struck by lightning, no one would ever build metal barns on the Midwestern plains. But they do and it's not a problem.

This is to be distinguished from how the different materials matter once lightning has decided to strike that object or a location nearby.

I don't even know about that. How many times you see taller, maybe even higher conductive objects that didn't get struck?

Think it is all about where charges are at the time and when they happen to be enough to overcome any resistance between them.

Possible that taller conductive objects may very well be more of a static drain and actually can see less severe hits, but the right situation and they still get hit at times.

 

[jaggedben]

I don't even know about that. How many times you see taller, maybe even higher conductive objects that didn't get struck?

Think it is all about where charges are at the time and when they happen to be enough to overcome any resistance between them.

Possible that taller conductive objects may very well be more of a static drain and actually can see less severe hits, but the right situation and they still get hit at times.

I don't think you're disagreeing with me. Lightning will strike in the spot that it wants to strike, based on where the potential reaches the critical point between sky and ground. It will strike a tall object within that pretty small zone (e.g. not strike directly to ground within a grove of trees) but otherwise is not very predictable.

The fact that the conductivity of the struck object doesn't determine where it strikes is somewhat analogous to how voltage drop doesn't show up when measuring open circuit voltage. Resistance only matters once the circuit is closed.

 

[zbang]

Folks probably ought to read this when discussing lightning-

Lightning FAQ

Frequently asked questions about severe thunderstorm forecasting, models and methodology, from the NOAA National Severe Storms Laboratory.

www.nssl.noaa.gov

Does lightning strike from the sky down, or the ground up?
The answer is both. Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up.

 

[grich]

...Possible that taller conductive objects may very well be more of a static drain and actually can see less severe hits, but the right situation and they still get hit at times.

Most of us broadcasters try to help that static drain along by adding stainless-steel devices that look a lot like bottle brushes to the top of our towers. The theory is each sharp point on the brush is an additional place to bleed static charges from the tower.

 

[zbang]

Dry paper-handling machines (printers/presses) often have some sort of tinsel across the paper path to grab any static created there.