ground rod at parking lot luminare pole base (again)

[Mike01]

I know that the ground rod at the light pole is not designed to trip the breaker on ground fault and that the code does not allow this but would it not act as a redundant ground also in the case of a lightning strike, it it tries to find the path of least resistance to ground it would take the majority of the energy to ground and if you fixture was wired with a #10 or even a #8 back to the panel a couple hunderd feet or so than the ground wire either #10, or #8 would act as a fuse and melt prior to the energy reaching the panel correct? is this all just a bunch of who-ha or good in theroy and really just a waste of money? I look foreward to hearing all of you thoughts, opinions, and experiences with this. thanks in advance.

 

[coulter]

...but would it not act as a redundant ground also in the case of a lightning strike

yes

...lightning strike, it it tries to find the path of least resistance to ground...

No. All paths to ground

...it would take the majority of the energy to ground ...

Why would the ground rod take the majority of the current? Does your light pole have a foundation? - in the ground? Isn't this foundation a good ground - in fact far superior to the earth rod?

...if you fixture was wired with a #10 or even a #8 back to the panel a couple hunderd feet or so than the ground wire either #10, or #8 would act as a fuse and melt prior to the energy reaching the panel correct? ...

I'm assuming you believe the pole has no foundation and any lightning induced currents have to travel to ground back through the grounding conductor. I don't know what the #8 or #10 would do. Have you done any calculations to see what the short term current rating of an #8 or #10 is? What size GEC were you going to run from the pole to the ground rod? Why wouldn't it just act like a fuse?

... is this all just a bunch of who-ha or good in theroy and really just a waste of money? ...

Some on this site say, "who-ha". Some will say it is a not a waste of money. I'd say it's a design issue.

...I look foreward to hearing all of you thoughts, opinions, and experiences with this. ...

Perhaps a forum search would give you all you are looking for. Have you done that?

carl

 

[dennis schaffert]

lightning

lightning

The ground wire that you run out to the pole is in fact a bonding jumper to the neutral of your power source with out it, a short to ground would not throw the breaker in a fault condition. This is why you bond your ground to the neutral at your main. The equipment grounding conductor and ground rod at the pole provide the shortest distance to ground for a lightning strike this could be millions of volts but normally low amperage. lightning has a tendency to conduct over the out side of a conductor rather than through it, if your ground rod is correctly installed driven flush with the ground you will dissipate the voltage to ground rapidly with few if any streamers. When improperly driven, say a ground rod 6 inch's above grade with a high resistance the lightning will then travel across the ground or just above striking anything and ever thing in the form of streamers as it searches for ground. What you witness is the equalization of potential positive and negative ,earth to atmosphere. But don't be fooled lighting can go up or come down. Hopefully the conductors leading to the pole will not be effected by the strike. Unfortunately many times the wiring does take a hit, usually because the system was not grounded effectively to start with and ultimately provides a path to ground for the lightning or some of its streamers. The worse the grounding method normally the worse the damage done normally indicated by how many appliances etc, it took out. Most lightning conductors are a mesh of wire rather than a solid conductor this dissipates the heat produced rapidly over the conductor. I suggest you review bonding and grounding. Also it is important to note that if you have to up size your conductor for voltage drop over along distance, you should also increase the size of your grounding conductor so as not to create a high resistance bonding / grounding path back to the main which is normally evidenced by a delayed trip of the breaker and sometimes a long audible short to ground

 

[Pierre C Belarge]

The ground wire that you run out to the pole is in fact a bonding jumper to the neutral of your power source with out it, a short to ground would not throw the breaker in a fault condition. This is why you bond your ground to the neutral at your main. The equipment grounding conductor and ground rod at the pole provide the shortest distance to ground for a lightning strike this could be millions of volts but normally low amperage. lightning has a tendency to conduct over the out side of a conductor rather than through it, if your ground rod is correctly installed driven flush with the ground you will dissipate the voltage to ground rapidly with few if any streamers. When improperly driven, say a ground rod 6 inch's above grade with a high resistance the lightning will then travel across the ground or just above striking anything and ever thing in the form of streamers as it searches for ground. What you witness is the equalization of potential positive and negative ,earth to atmosphere. But don't be fooled lighting can go up or come down. Hopefully the conductors leading to the pole will not be effected by the strike. Unfortunately many times the wiring does take a hit, usually because the system was not grounded effectively to start with and ultimately provides a path to ground for the lightning or some of its streamers. The worse the grounding method normally the worse the damage done normally indicated by how many appliances etc, it took out. Most lightning conductors are a mesh of wire rather than a solid conductor this dissipates the heat produced rapidly over the conductor. I suggest you review bonding and grounding. Also it is important to note that if you have to up size your conductor for voltage drop over along distance, you should also increase the size of your grounding conductor so as not to create a high resistance bonding / grounding path back to the main which is normally evidenced by a delayed trip of the breaker and sometimes a long audible short to ground

Dennis
Where have you gotten this info from?



My understanding of a lightning event tied into "our" electrical system.

Lightning is a very high frequency event. Because of this, the 10 or 12 AWG EGC from the pole back to the building is of very high resistance to the lightning event.
The lightning will see the relatively 'smaller resistance' of the GEC to the ground rod as its path to earth, hence little if any of the lightning current will travel along the EGC to the building with the GEC installed to the ground rod at the base of the pole. That coupled with the concrete pier of the pole will help to complet the dissipation of the lightning to earth.

or something close to this anyway.:wink:

 

[dennis schaffert]

lightning

lightning

regardless of the frequency you must remember that voltage is a pile driver the higher the voltage the more the ability to travel over long distances resistance plays a smaller part.The first duty of the grounded conductor from the panel is to provide a path of reference back to the power source thus you should ground directly to your apparatus. Your equipment ground driven at the pole does not act as a secondary means of ground for your panel and should or will be the path of least resistance that the lightning follows to ground. Yes you are correct the small guage wire does have a high resistance but that resistance means nothing when the equipment ground fails I guess you could say it is similar to a fault normally V or higher that trips a second down stream breaker passing through the first breaker so rapidly to trip it. remember the breaker is sensing amperage not voltage you asked how I learned this I was forced to research lightning on a number of jobs were I encountered old lightning rod systems that in fact posed a greater risk to life and property than protection. also the government has published a lot on lightning after loosing a large number of ammunition dumps to lightning new techniques were established that we use today
Dennis

 

[dennis schaffert]

lightning

lightning

I should clarify that I am not saying that you should provide a isolated ground to the pole the equipment ground or steel structure should all be bonded together to form a complete grounding system this should be accomplished, what I am saying is, if you have not! provided a low resistance equipment ground path to the earth your conductors become the next shortest path regardless of there high resistance. Here is an old trick take a metal rod tape it up to a single conductor directly to a breaker stretch it out side and puss it in the ground and the worms come up. you will note that the breaker will not trip especial on a ungrounded system . Why because there is no reference to ground on the neutral conductor. That voltage will flow for ever, Just remember when you go to grab the worm your going to get bit. there in lies the need to provide a bond to ground at the main providing a reference

 

[coulter]

... also the government has published a lot on lightning after loosing a large number of ammunition dumps to lightning new techniques were established that we use today...

Perhaps you could give us some these references.

carl

 

[iwire]

regardless of the frequency you must remember that voltage is a pile driver the higher the voltage the more the ability to travel over long distances resistance plays a smaller part.

Dennis frequency plays a much larger part then you are giving it credit for. I agree with Pierre.

I also agree with Carl that the fact the pole has a foundation is going to do a lot more than the added ground rod.

 

[dereckbc]

the government has published a lot on lightning after loosing a large number of ammunition dumps to lightning new techniques were established that we use today
Dennis

This is true, the work was actually done by DuPont Corp by a scientist by the name of Herbert G Ufer. Ammunition depots in Arizona being struck by lightning were blowing because the ground system employing driven rods were useless in the dry Arizona soils. The solution Mr. Ufer designed bears his name today with the UFER ground, which is basically the foundation of the light pole and the basis of the NEC CCE.

 

[winnie]

Which suggests that the most important thing to do is to make sure that the pole is bonded to the rebar in the foundation. Is it usually the case that the pole mounting bolts are tied to the rebar? Is there any benefit to having an explicit GEC conductor that uses a suitable clamp to connect the pole to the rebar?

-Jon

 

[iwire]

Is it usually the case that the pole mounting bolts are tied to the rebar?
-Jon

Jon it depends on the job specs.

Few jobs I have worked on required re-bar tied to the mounting studs.

Many light pole bases in this area have no re-bar at all.

Typically the mounting studs are J-Bolts 5/8" to 1" in diameter and 18" to 30" long. Many times they are just placed into the base shortly after pouring the concrete.

If this picture had 4 J-Bolts instead of 6 it would look like how I usually install the J-Bolts into the pole base.

That said I don't see why it would make much difference if we have just the J-Bolts or they are tied to re-bar, either way we are using steel round stock as the electrode.

 

[dennis schaffert]

lightning

lightning

Looking back into some records I find that one good place to look for information is the NLSI ( National Lightning Safty Institute ) You will find information regarding the suitability of the foundation as grounding Medium although you will find that it is critical that the rebar be connected to the grounding electrode this would include the anchor bolts therefor providing a suitable path to ground from the pole via the bolted attachment of the pole its self. also NFPA 2001 780 . I should correct my self now that I have dug up some old info is that the normal current magnitudes is 20-30KA way higher than I remember. Also NLSI gives a much better explanation than mine concerning voltage potential if I may quote ( Lightning will follow the path of lowest inductance, the higher the frequency, the higher the inductive reactance value in calculating the total impedance of the circuit, Resistive values can be eliminated for all practical purposes in high frequency lightning conductor calculations for distances approximatly 2000 feet or less ) Links are also provided via the NLSI to many other educational information and the IEEE. All in all the education one will recieve is the importance of correctly installing ,bonding and connecting the ground protection system. All to often many electricians do not understand fully what they are doing and are simply connecting a ground rod to a light pole to satisfy the inspector that they have provided a ground not fully realizing that the grounding is as much of circuit as the working circuit they provide to an apparatus a good comparison would be that of a wet and dry sprinkler system your branch circuit conductors are the equivalant to a wet system carrying power. your ground system is the equivalant of a dry system intact waiting for power. unfortunatly many people do not percieve the importance of the grounding system to be as important as there branch circuit system because its dry .I look at it this way, if as a contractor you are required to install lightning protection it is important that you understand the importance of what you are installing and that it is installed correctly and inspected as well as documented this limits your liability, because lightning is a funny thing and even the best laid plan can fail if you have done everything correctly you can not be held liable when the impossible occures like multiple strikes at once

 

[dennis schaffert]

rebar

rebar

I also read that in many cases rebar is not placed in a foundation and any of us that have poured a pole base knows how difficult it can be, so naturally the bolts are most often pushed in after you have poured you can attach to at least one of those bolts a ground tail brought up through the tube connected to a suitable pipe clamp and pushed back down with the bolt. In the complete absence of rebar one then relies on the ground connection point and the ground rod the importance here would be driving your rod into undisturbed soil or compacted earth not dropping it into the hole next to your sona tube

 

[iwire]

Dennis, could you give a brief answer to this question?

What do you feel a ground rod added to a typical pole base will do?

All to often many electricians do not understand fully what they are doing

That is not the case here.

Discounting myself, the people responding to this thread understand grounding very well.

 

[dennis schaffert]

Ground rod

Ground rod

the utilization of the ground rod provides a single point ground again eliminating as much as possible additional streamers

 

[iwire]

the utilization of the ground rod provides a single point ground again eliminating as much as possible additional streamers

But it is not a 'single point ground'

The pole is in fact grounded through it's foundation regardless of the fact the NEC does not recognize a pole base as a concrete encased electrode.

It is also still required to be connected to the buildings EGC.

I find it almost imposable to believe that the addition of a ground rod at a pole will add anything at all to the electrical systems safety.

 

[dennis schaffert]

concrete

concrete

Quoting NLSI ( concrete is alkaline and hydroscopic ( absorbent) in nature this type of ionizing and moist medium can create a large and effective earth sink). This is not always conveniently true the pole base may be in a very dry climate or it may be totally surrounded by aggregate.
Although a concrete encased electrode has prooven to be a beneficial component.
if you fall back to the periodic table of conductors concrete is not considered as a conductor and would be more classified as a semi conductor because of its ability under certain conditions to act as a conductor, were as your copper wire and ground rod are considered suitable conductors at all times.
referring back to the above quote the words (can create) are used , not will or does.

 

[iwire]

if you fall back to the periodic table of conductors concrete is not considered as a conductor

So that would mean a NEC concrete electrode is worthless in the dry desert...but that is just the type of conditions Ufer was working with for the ammo dumps.

Cement carries electricity just fine for the purposes of a grounding electrode.

 

[don_resqcapt19]

Dennis

if you fall back to the periodic table of conductors concrete is not considered as a conductor and would be more classified as a semi conductor because of its ability under certain conditions to act as a conductor, were as your copper wire and ground rod are considered suitable conductors at all times.

But the ground rod is connected to the earth and that acts the same as concrete.
Don

 

[dennis schaffert]

dry desert

dry desert

Nikola Tesla encounter exactly that when he was performing his high voltage experiments in Colorado springs in the 1800s. the inability to get a good ground .
His notes indicate that he saturated the ground with water to accomplish the feat. Theoretically it would seem that as you said, concrete under those conditions is a very poor ground. and just because the code states that it is does not mean that every scenario was anticipated in their conclusion and can be wrong in certain geographic areas
As new findings occur the code is evaluated and changed , thus the beauty of advancement