Pole Lights and Ground Rods

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I have been having a reoccurring debate with a few old timers from work about pole lights. They keep insisting that a ground rod must get driven at every pole light. My fear is that they are telling me this simply because they have always done it this way. From my understanding, there is no real advantage to having a ground rod at every pole. I can't find anything in the code about it. The pole lights are regular 120v lights coming from an already grounded system.

On the job in question, there is nothing in the specifications requiring ground rods.

Any and all code references, comments, and input would be appreciated. Thanks in advance!

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iwire

Moderator
Staff member
Location
Massachusetts
Unless the pole light is supplied by more than one branch circuit, or a feeder the NEC does not require a grounding electrode at the pole.
 

mgookin

Senior Member
Location
Fort Myers, FL
I have been having a reoccurring debate with a few old timers from work about pole lights. They keep insisting that a ground rod must get driven at every pole light. My fear is that they are telling me this simply because they have always done it this way. From my understanding, there is no real advantage to having a ground rod at every pole. I can't find anything in the code about it. The pole lights are regular 120v lights coming from an already grounded system.

On the job in question, there is nothing in the specifications requiring ground rods.

Any and all code references, comments, and input would be appreciated. Thanks in advance!

Sent from my XT1254 using Tapatalk

Are they installing lightning protection to keep the surge from going back to the panel maybe?

PS Welcome to the forums.
 

iwire

Moderator
Staff member
Location
Massachusetts
So you want to send 100% of it to the building? That lightning strike is wanting to go to Earth.

The strike just went miles through the air, it will make it through the pole base into the earth with no problem.

With or without the rod some of the strike energy is heading for the building via the EGC anyway.
 

jumper

Senior Member
The strike just went miles through the air, it will make it through the pole base into the earth with no problem.

With or without the rod some of the strike energy is heading for the building via the EGC anyway.

I never even heard of putting rods at light poles till I joined this forum. Have personaly never seen it done, but some here say it is often speced.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
Unless the pole light is supplied by more than one branch circuit, or a feeder the NEC does not require a grounding electrode at the pole.
And the appropriate reference is article 250.32(A). It starts by saying each separate structure (and a light pole counts as being a structure) shall have a grounding electrode system. It then gives an exception that says you don't need a grounding electrode system if the structure (light pole) is fed from a single circuit (including, if appropriate, a multi-wire branch circuit) that includes an equipment grounding conductor. That is why Bob's statement about more than one branch circuit or a feeder is correct.

 

charlie b

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Retired Electrical Engineer
I never even heard of putting rods at light poles till I joined this forum. Have personaly never seen it done, but some here say it is often speced.
I have seen it in the design details that some engineering companies include in their design packages. Whenever I have seen it, I tell the CAD person to delete it. I did have one disagreement with a client on this point. I told him that I believed a ground rod was not needed and would serve no purpose other than to cost the client money. He said he agreed with that, but he wanted it anyway. So he got it.

My real concern over this question is over the people who believe (incorrectly) that a ground rod at a light pole is a necessary safety feature, and that when a person (or animal) receives a shock from touching a light pole it was because there was no "proper" ground rod present.

 

George Stolz

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Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
So you want to send 100% of it to the building? That lightning strike is wanting to go to Earth.

Look at this another way; do you believe that a ground rod is going to make any difference in the voltage to earth in the event of a direct strike, measured either inside the building or at the pole? The EGC taking a few hard left turns underground is likely to stave off that energy far more than the rod's contribution.
 

user 100

Senior Member
Location
texas
I am saying adding an 8' x 5/8" metal rod is not going to do a thing for lightning protection that the large concrete base is not already doing.

:thumbsup:. With an average lightning strike's energy measuring something like in the tens of thousands of amps and millions of volts, I doubt very seriously that adding that rod on top of all of that concrete and rebar is going to provide that much more of a mitigating factor.:)
 

tom baker

First Chief Moderator
Staff member
It will, right through the pole base. I have serious doubts the rod will provide any additional protection of significant value.

I have an engineering report that states the reinforcing steel and concrete in the base are a very effective ground, better than a ground rod. But if you are concerned about lighting entering the building on the branch circuit, then provide an SPD on the lighting branch circuit.
 

cad99

Member
Location
ND
All that is needed is a ecg. The rod would have to be as tall as the lighting standard to be of any real benefit. Mr. Holt has a video on this subject.


Living the dream one nightmare at a time
 

Fulthrotl

~Autocorrect is My Worst Enema.~
I have an engineering report that states the reinforcing steel and concrete in the base are a very effective ground, better than a ground rod. But if you are concerned about lighting entering the building on the branch circuit, then provide an SPD on the lighting branch circuit.

yeah, the strike is going to take *all* paths to ground, and lightning
is sometimes fickle, as it doesn't read the code, but just does what
it wants.

http://en-us.fluke.com/community/fl...rport-tower-lightning-protection-systems.html

(fluke infomercialing us and attempting to sell another $3k whiz bang meter)

"Lightning protection components at a glance
  • An air terminal, down conductor, and at least one ground plate or rod for each beacon tower, should be installed.
  • The air terminal should be installed at the top of the tower with the tip of the rod extending not less than 150 mm (6 in) above the top of the beacon.
  • Down-conductor cables should be securely fastened to the surface of the tower leg at 150 cm (5 ft) intervals with suitable bronze fasteners having bronze or noncorrosive metal bolts. Sharp turns or bends in the down conductor are not permitted.
  • All connections of cable-to-cable, cable-to-air terminals, and cable-to-ground plates or rods must be made with solderless connectors or noncorrosive metal.
  • The down-conductor cable shall be securely attached to ground rods or plates placed at least 60 cm (2 ft) away from the tower foundations. The ground rod shall be driven into the ground so that the top is at least 150 mm (6 in) below grade. The down-conductor shall be firmly attached to the ground plate or rod by means of a ground connector or clamp.
If an airport is located in an area with a high incidence of lightning, the Catenary System (used to protect the Space Shuttle) can be used but would be very costly. Sandia National Laboratories (SNL) recommends a less costly (but equally effective) alternative. SNL recommends installing a ground ring complemented with ground rods and radials.
 
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