Grounding wooden poles

[kbsparky]

We have an upcoming project that will utilize about 10 wooden poles. Mounted at the top of these poles will be stadium lights for a ball field.

When dealing with 50 foot poles out in the middle of a field, they are the highest point around, and a target for lightning. Good grounding should minimize any risk of equipment damage.

I want to ensure that the light fixtures and associated mounting hardware have sufficient grounding -- in addition to any equipment grounding conductors present.

That being said, I propose to use what is commonly called "butt grounding" -- a coil of bare copper ground wire wrapped on the bottom of the poles, and/or a grounding plate attached to the bottom of the pole, with a #6 wire leading up the pole and attached to any steel structure present. Manufacturer's literature suggests that such grounding is superior to using driven ground rods adjacent to the pole.

What have been your experiences in grounding wooden poles?

 

[iwire]

What have been your experiences in grounding wooden poles?

I usually use nylon rope. :grin:


I don't think it will matter one bit if you use a rod, a butt plate or just bury the end of the #6 in the ground. Either way lighting will find the dirt.

I guess you should really be using that braided down lead copper that lightning protection systems use, there must be a reason they use it.

 

[Pierre C Belarge]

When dealing with 50 foot poles out in the middle of a field, they are the highest point around, and a target for lightning. Good grounding should minimize any risk of equipment damage.

I want to ensure that the light fixtures and associated mounting hardware have sufficient grounding -- in addition to any equipment grounding conductors present.

That being said, I propose to use what is commonly called "butt grounding" -- a coil of bare copper ground wire wrapped on the bottom of the poles, and/or a grounding plate attached to the bottom of the pole, with a #6 wire leading up the pole and attached to any steel structure present. Manufacturer's literature suggests that such grounding is superior to using driven ground rods adjacent to the pole.

What have been your experiences in grounding wooden poles?

The portion I highlighted green caught my attention.
I am not sure that any ground scheme will keep equipment from getting damaged/fried during a direct or close strike.
It may help reduce some damage during an indirect strike.

I would think that the grounding will reduce or eliminate the chance the lightning will find its way back into the building if the grounding is at least of minimum protection based on the proper installation.

 

[kbsparky]

Places like radio stations transmitters utilize massive grounding grids -- they can take direct lightning hits and never miss a beat.

In my application, there is no building involved. The service is an outdoor pedestal, and there are underground lines going to the various poles for the lighting circuits. Each underground line has a suitable EGC, but for increased protection, we thought it would be prudent to install these supplemental butt grounds on the bottoms of all the poles. We are essentially connecting the steel angle iron strut at the top of each pole to these butt grounds.

If the power companies do it, it must be for good reason, since their poles get hit all the time by lightning strikes.

 

[M. D.]

yeah,. it will find the earth all right ,.. and it can be quite spectacular while it is doing it ,... You may want to consider recommending a lightning protection system be installed.

 

[tom baker]

The National Grounding Reseach Project lists a pole butt ground as the worst, or highest resistance of any grounding electrode.

 

[LarryFine]

The National Grounding Reseach Project lists a pole butt ground as the worst, or highest resistance of any grounding electrode.

Well, don't keep us in suspense; what's the best???

 

[hurk27]

Well, don't keep us in suspense; what's the best???

UFER:roll:

 

[M. D.]

UFER:roll:

Not according to this ,..a five year study

http://www.electro-specialties.com/technical/downloads/Ground Rod Study.pdf

......Of all the
electrodes tested in Phase 1, only one electrode, E did
not have at least one resistance reading over 25 ohms at
any of the five sites over the test period. In addition, the
E electrode exhibited the most stable resistance values
of all the electrodes tested for all five sites, based on the
deviation between minimum and maximum resistance
values.........

.......The E electrode is the 2.4m
long copper-bonded ground rod encased in GEM
(ground enhancement material). ERICO GEM, is a very
low resistivity material (0.12 ohm-meter or less) that is
either installed dry (and allowed to absorb moisture
from the surrounding earth) or premixed in slurry
(similar to concrete). It is then poured into an augured
hole of given diameter with a standard copper-bonded
ground rod centered in the hole. The GEM sets up
permanent like concrete and does not leach any
compounds into the surrounding soil.........

 

[Pierre C Belarge]

I did not read the whole study, but it looks fairly thorough.

I can say that some manufacturers who provide studies and then come up with results that show one of their more expensive products to be the best of all items just makes me wonder...

 

[hardworkingstiff]

Not according to this ,..a five year study

http://www.electro-specialties.com/technical/downloads/Ground Rod Study.pdf

I scanned the pdf, which item letter in table 1 was the UFER test?

 

[M. D.]

Well here is one sponsered by the NFPA ..

http://lecglobal.com/info/tech-papers/negrp-grounding-rod-comparison.pdf

The National Electrical Grounding Research Project (NEGRP) was a project managed and
sponsored by the National Fire Protection Association (NFPA) Research Foundation.

At all five sites, Electrode R is a ten foot long LEC Chem-Rod backfilled with Grounding
Augmentation Fill (GAF). At the sites other than the one in Nevada, Electrode Y is a ten foot
long horizontal Chem-Rod backfilled with GAF. GAF is a conductive material made for
backfilling around any type of grounding electrode.

As you can see from the test data, the lowest resistance readings are consistently generated by
Electrodes R and Y. For example, at the Nevada site, the lowest reading is 18 ohms by Electrode
R. In another example, at the Virginia site the lowest reading is 10 ohms by Electrode R3, while
the second lowest reading is 11 ohms by Electrode Y2.

 

[M. D.]

I scanned the pdf, which item letter in table 1 was the UFER test?

I will stand corrected as there is no foundation /footing there is no concrete encased electrode

 

[Pierre C Belarge]

MD
Thanks for taking the time to locate and post the PDFs.

 

[hardworkingstiff]

I will stand corrected as there is no foundation /footing there is no concrete encased electrode

I'm not trying to correct anyone, just become more knowledgeable. I also would like to thank you for posting the information. It clearly shows there are better grounding methods than what we typically use.

 

[iwire]

I'm not trying to correct anyone, just become more knowledgeable. I also would like to thank you for posting the information. It clearly shows there are better grounding methods than what we typically use.

To me the question becomes do we need 'better electrodes'?

Does an electrode with 10 ohms to ground really provide any safety or function benefits over a 100 ohm rod when we are talking about lightning protection and / or premises system wiring voltages?

 

[hurk27]

For the most part , Coke is one of the lowest ground enhancement one can find, that doesn't require allot of maintenance, the biggest problems, you will find with cem-rods and enhanced rods, is they are very rarely maintained, thus leading to failure at having higher resistance. I would not include a ground enhanced electrode in any studies as we can not use them when installing to the NEC, home owners are not going to maintain them.

I have used Coke (very high in carbon) and it will last for a long time, and is one of the most preferred methods of enhancing the Earth around an electrode.

This chart will show the resistance of different soils and can be found HERE:

Material Resistivity Ω-m
Ashes 3.5
Clay soil - 40% moisture 7.7
Clay soil - 20% moisture 33
Clay - London 4-20
Clay - very dry 50-150
Chalk 50-150
Coke 0.2-8
Consolidated Sedimentary rocks 10-500
Garden earth 50% moisture 14
Garden earth 20% moisture 48
Gravel - well graded 900-1000
Gravel - poorly graded 1000-2500
Gravel clay mixture 50-400
Peat 45-200
Sand - 90% moisture 130
Sand - normal moisture 300-800
Sand clay mixture 200-400
Surface Limestone 100-10,000

 

[Pierre C Belarge]

To me the question becomes do we need 'better electrodes'?

Does an electrode with 10 ohms to ground really provide any safety or function benefits over a 100 ohm rod when we are talking about lightning protection and / or premises system wiring voltages?

I would also like to know if this is really necessary for standard residential and small commercial installations.

I know this is an area of the industry where there are distinctly differing views.

I am going to pose this question to some at the Eastern Section Meeting this weekend and see what answers I get.
In the past, CMP 5 usually has a very good presence at this section, I will let you know what they say.

 

[hurk27]

I would also like to know if this is really necessary for standard residential and small commercial installations.

I know this is an area of the industry where there are distinctly differing views.

I am going to pose this question to some at the Eastern Section Meeting this weekend and see what answers I get.
In the past, CMP 5 usually has a very good presence at this section, I will let you know what they say.

With the results found in this THREAD

we see that basically as the conductivity of Earth increases, the sphere of influence decreases, and this can increase the shock hazard, as higher voltages will be available closer surrounding the electrode, so touch potential, is increased. so instead of 90 volts at the 3 foot mark, you might have 105 volts.
but on the other hand you could reach the point where 15 amp OCPD would open as Gary found out, but what about all the higher amperage circuits. so over all, it would be in my opinion that even having a better electrode, as far as an NEC requirement, would lead to a higher potential of touch and shock hazard, and is probably one of the best reasons to get rid of the requirements for grounding rods, and some of the other electrodes.

 

[Pierre C Belarge]

With the results found in this THREAD

we see that basically as the conductivity of Earth increases, the sphere of influence decreases, and this can increase the shock hazard, as higher voltages will be available closer surrounding the electrode, so touch potential, is increased. so instead of 90 volts at the 3 foot mark, you might have 105 volts.
but on the other hand you could reach the point where 15 amp OCPD would open as Gary found out, but what about all the higher amperage circuits. so over all, it would be in my opinion that even having a better electrode, as far as an NEC requirement, would lead to a higher potential of touch and shock hazard, and is probably one of the best reasons to get rid of the requirements for grounding rods, and some of the other electrodes.

I appreciate what Gary did, he really worked hard in providing us with his experiment. I am curious how practical it really is.

In regards to your comment about shock hazard, is that the reason behind installing electrodes and the grounding electrode system?