Light Poles and Grounding Electrodes

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iwire

iwire

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OK it often comes up that engineers have specified ground rods at light poles.

The standard answer is that they are not required by the NEC.

What happens when there is more than one circuit at the pole, wouldn't 250.32(A) require a grounding electrode?

One could be for a receptacle outlet and the other for the lights. Or there could be two circuits on one pole.

250.32 Two or More Buildings or Structures Supplied from a Common Service.

(A) Grounding Electrode. Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in Part III of this article at each building or structure shall be connected in the manner specified in 250.32(B) or (C). Where there are no existing grounding electrodes, the grounding electrode(s) required in Part III of this article shall be installed.

Exception: A grounding electrode at separate buildings or structures shall not be required where only one branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non?current-carrying parts of all equipment.
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Re: Light Poles and Grounding Electrodes

Bob,
Maybe exception #3 to 225.32 should be added to 250.32(A). You are correct under the current code a light pole with multiple circuits requires a grounding electrode system.
Don
 
Re: Light Poles and Grounding Electrodes

I would prefer the definition of structure to be defined better. Claiming a light pole is a separate structure being served by a common service is too much of a stretch for me.

And besides, as Don points out, multiple branch circuits to a separate structure is a violation of 225.30, but that is never enforced. So in my opinion, its got to be one way or the other. If the poles are separate structures, then they must be completely treated as separate structures, but I would prefer them to not be called structures, thus elimanting the 225.30 and 250.32 issue.
 
Re: Light Poles and Grounding Electrodes

Bryan, I agree with your post hands down.

Roger
 
Re: Light Poles and Grounding Electrodes

Originally posted by bphgravity:
And besides, as Don points out, multiple branch circuits to a separate structure is a violation of 225.30, but that is never enforced.
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Where does Don point that out? :D

Don's post is about the exception for a disconnect means at a light pole.

225.30(D) in my opinion allows more than one branch circuit to a light pole. "different uses"

I am fine with the definition of structure I think it works well, unless it grew from nature it is a structure. :p

Bob
 
Re: Light Poles and Grounding Electrodes

Since the light poles are on the same premises as the building, do you bond the grounding electrodes together with the grounding electrodes at the building? 250.50
 
Re: Light Poles and Grounding Electrodes

Why is anything besides an EGC needed at all?

Roger
 
Re: Light Poles and Grounding Electrodes

Per the current wording, if I install a branch circuit to a light pole in my front yard and add an additional branch circuit for a receptacle on that same pole, I now am required to install a grounding electrode?

What would be the purpose? Lightning protection? I'm not a big fan of connecting to ground at several points for one system. It creates to many paths for return current.

I guess I misread and misunderstood the point of Don's post. I saw "225" and my brain went right to the 225.30 requirement. My mistake.
 
Re: Light Poles and Grounding Electrodes

Originally posted by bphgravity:
Per the current wording, if I install a branch circuit to a light pole in my front yard and add an additional branch circuit for a receptacle on that same pole, I now am required to install a grounding electrode?
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I agree.

What would be the purpose? Lightning protection?
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That is my question also, I was thinking an exception like Don suggested would be appropriate.

I'm not a big fan of connecting to ground at several points for one system. It creates to many paths for return current.
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We differ there, I do not see the problem in that.

It is essentially already connected to ground through the pole base, just not though a NEC recognized electrode.

Bob
 
Re: Light Poles and Grounding Electrodes

Bryan,
What would be the purpose? Lightning protection? I'm not a big fan of connecting to ground at several points for one system. It creates to many paths for return current.
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I differ in that as many points of earth that are contacted in a surge or Lightning event will definitely assist the dispersion of the offending voltage.

Roger
 
Re: Light Poles and Grounding Electrodes

Oh, I agree when it comes to lightning. When your 1 in 40,000,000 chance lightning hits the pole, it would probably be good having an electrode there.

However, for the other 99.99999% of the time, all you have is another return path of normal operating current. Is it objectionable? I guess that would depend on the specific installation.

Everyone likes to claim the solution to lightning is grounding. I find the best method is to simply not put a building or structure anywhere lightning is going to strike. Easy enough, right? ;)
 
Re: Light Poles and Grounding Electrodes

Originally posted by bphgravity:
Everyone likes to claim the solution to lightning is grounding. I find the best method is to simply not put a building or structure anywhere lightning is going to strike. Easy enough, right? :D

The perfect solution. :cool:
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Re: Light Poles and Grounding Electrodes

Bryan, in the 10 years I have lived in the home I reside in now, (N.C.) I have been hit 7 times, this far out does the 34 years I lived in Manatee county.

If 40,000,000 times is a rarity, I wish my luck would follow suit in playing the lottery. ;)

Roger
 
Re: Light Poles and Grounding Electrodes

Well since this is a crowd I respect, let me put a twist to it. What is the difference between a light pole and a communications tower with a beacon or strobe? I can guarantee you a radio tower is a proven multi-ground application.
 
Re: Light Poles and Grounding Electrodes

An outdoor metal lighting pole supplied by a branch circuit must be supplied by an equipment grounding conductor run with the branch circuit conductors. The EGC must be connected to the metal pole and a bonding jumper installed between the base and the metal pole if it is hinged. See Exhibit 410.4 on page 464 of the 2002 NEC Handbook. In addition, a grounding electrode is not required and would serve no useful purpose, the concrete base and footing with re-bar is a better grounding electrode than an 8 ft. copper-clad ground rod. Besides, driving a ground rod within 6 ft of the pole base would be within the sphere of influence of the concrete base.
 
Re: Light Poles and Grounding Electrodes

Hello John, welcome to the forum. I agree with your answer but you did not address the opening issue. Take a look at the first post in this thread.

After that, take a look at this thread. The fifth post could destroy the NFPA!
 
Re: Light Poles and Grounding Electrodes

Hello John Welcome.

By Bryan: What would be the purpose? Lightning protection? I'm not a big fan of connecting to ground at several points for one system. It creates to many paths for return current.
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It shoudln't create any path for return current as the only current on a EGC or the grounding electrode should only be fault current.

I agree with Bob as the code is now multiple circuits will require a grounding electrode system And only multiwire circuits won't

Looks like a candidate for a change. :D

Anyone keeping notes on these codes we find that we are having problems with, like 250.148 not being clear on when a EGC needs to bond to a box when a grounded metal raceway is used?
It would be nice to make a list of them in the proposal forum and create proposals to clear them up for "2008" ;)
 
Re: Light Poles and Grounding Electrodes

The electrode at the pole is bonded to the pole which is also bonded to the EGC. The EGC is bonded to all metallic enclosures and the branch circuit panelboard. The EGC serving the panelboard is bonded to the service grounded conductor at the main bonding point, which is also the point the system grounding electrode is bonded.

It is well established that some normal operating current flows over the GES as the utility source is also grounded at the transformer location. Most should flow over the utility grounded neutral conductor, but not all.

Now there is another path as stated above. Again, Ohm's Law will show if objectionable current will flow or not. I think in a worse case scenerio alot of current can flow through this path, such as an open service neutral.

Some will argue that we don't necessarily install systems for what might happen, but then again this whole discussion is about lightning, which is something that might happen.
 
Re: Light Poles and Grounding Electrodes

Roger,
In view of your comment to Bryan, I tried to show how one can make estimations regarding lightning strikes.

ESTIMATING THE PROBABILITY OF A POLE BEING STRUCK BY LIGHTNING

If you have a map showing the flash density across the United States < www.lightningsafety.noaa.gov >, you can easily estimate the probability of a pole being struck by lightning in a given region, say,in Florida, and in a given period of time, say, of 50 years.
You can proceed as follows:
1- From the map, you get, in Florida, a density of N = 90 flashes/year/sq.km.
2- Let us say the pole is 10 m (33 ft) high. Therefore, the pole collection area is given by a circle of 10 m radius, with an area A = 314 m2.
3- Then, the number of flashes per year to the pole is f = N*A*E-6, that is, f=0,00345 flashes per year.
4- In a period of t = 50 years, the mean number of flashes is m = f*t, that is: m = 0,1727 flashes. With this value of m and assuming that lightning strikes the pole according to Poisson Distribution ( Pt(k) = exp(-m + k*Ln(m))/k! k=0,1,2,3,?), one has:
?The probability of no one lightning strike to the pole in the 50 years period is 84 % ( P50(0) =exp(-0,1727 + 0*Ln(0,1727))/0!).
?The probability of at least one lightning strike to the pole in the 50 years period is 16%.
 
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