pole bases once and for all

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captainkevin

Member
Location
Missouri
ok - standard lighting pole base support with pvc conduit and a continuous ground from the panel to each pole and up to the fixture. Why do these consultants keep showing a ground rod at each pole base? If it is required someone please point me in the right direction. If you do add a rod at each pole do you have to bond the rebar in the pole base?
 

charlie

Senior Member
Location
Indianapolis
Re: pole bases once and for all

Ground rods are not for fault current protection, they are for lightning, higher voltage line contact, ground reference, etc. Please notice the first item on my short list (see 250.4). You are installing 30, 40, 90 feet, and even taller lightning rods in the form of lighting standards. Would it be better to install a ground rod at each column and tie it to the grounding conductor or let the lightning go through the building to find the grounding electrode (going through the lighting circuit and service equipment on the way)?

You are correct, the Code doesn't require the supplemental electrodes but that is the reason the consultants are calling for them. Bonding to the rebar is not required any more than bonding to the rebar in a foundation of a building. However, if it is available, why not? :cool:
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: pole bases once and for all

Charlie, I couldn't agree more. If you do not add the additional rods, lightning will travel through the EGC back to the building. Why ask for it?
 
Location
Colorado
Re: pole bases once and for all

Driving a ground rod at a standard 120/208 or 277/480 pole light serves no purpose what so ever.

The only way to properly ground your pole light is to run an equipment grounding conductor from the source panel to the pole as you have done.

Ask you consultants why they do it, I bet they will not be able to provide you with an intelligent documented response, because it does not exist.
:)
1.Ground Rods(GR) do not assist in clearing ground faults.
2.GR do not significantly reduce touch potential.
3.GR do not create an equipotential plane to reduce touch voltage.
4.GR do not assist in protecting poles from lightning.
5.GR do not assist in protecting concrete pole bases.
6.GR do not assist in protecting interrior wiring from lightning transient voltages.

I hope this helps. There is no other way to put it, but to say the people who put ground rods at these type of pole bases just don't know any better.
 

tom baker

First Chief Moderator
Staff member
Re: pole bases once and for all

Mike H.wonders the same thing. The ground rod serves no real purpose, however some of the reasons why installed may be:
1. Can't hurt, it will lower overall ground system resistance
2. Specs come from civil side, they don't understand purpose of ground rods
3. Lack of understanding even in electrical industry about purpose of ground rods.

Mike H. has a great section on this topic in his 2002 Grounding and Bonding text.
 

charlie

Senior Member
Location
Indianapolis
Re: pole bases once and for all

Tom & Chuck, why do you feel like lightning will not partially disipate at the column ground rods? Lightning is looking for earth and will find it somewhere, it is not looking for a fault current return path to a transformer. As a result of numerous ground rods and the fact that lightning doesn't like to make hard corners, most will disipate into the earth before it reaches the building unless you have high impedance ground rods.
 

captainkevin

Member
Location
Missouri
Re: pole bases once and for all

Thanks everyone - just what I thought a nice to do but not necessary. When I was doing Gov't computer room design per the FIP's 94 document they always preached the least amount of ground sources as possible to eliminate ground loops and potential variations in the best ground path. A good continuous ground path sized properly is still your best bet.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: pole bases once and for all

Chuck, what is lightning looking for? Why would 800.40, 810.21, 820.40, 830.40 and other related codes require connection to a GE if an EGC in the equipment were adequate?

I agree with most of your preceptions about ground rods except for lightning protection. There are multiple documents out there that attest to this availible from NFPA, ANSI, IEEE, TIA, EIA, National Lightning Institute, and others.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: pole bases once and for all

Dereck,
I agree with most of your preceptions about ground rods except for lightning protection. There are multiple documents out there that attest to this availible from NFPA, ANSI, IEEE, TIA, EIA, National Lightning Institute, and others.
Is there really? Wasn't NFPA 780 almost withdrawn because there is not adequate technical support as to how and even if the Franklin lightning rod system works?
Even if we assume that a rod is effective for lightning protection at light poles, is the addition of a rod any improvement over the grounding electrode that is created by the concrete base and the rebar cage?
Don
 

tom baker

First Chief Moderator
Staff member
Re: pole bases once and for all

"I agree with most of your preceptions about ground rods except for lightning protection. There are multiple documents out there that attest to this availible from NFPA, ANSI, IEEE, TIA, EIA, National Lightning Institute, and others"

Dereck: Mike Holt and myself have looked into this and tried to find any standard that states a ground rod at a metal lighting poles provides lighting protection.

If you can quote a standard or research paper I would like to see it and review it.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: pole bases once and for all

Don, if the rebar in the concrete was used (ufer), then a ground rod would not add much value, it serves the same purpose. The only point I am trying to make is the EGC is not a good discharge path for lightning. I think it is better to bleed the charge off directly to ground rather than through the facility wiring.

If it were me I would also add TVSS to the circuits where they leave the building to bleed off any excess charge. It is a design issue.
 
Location
Colorado
Re: pole bases once and for all

Charlie and Dereck, Tell me how a ground rod at a lighting pole protects you interior electrical system?

Lightning is an "arc" that temporarily neutralizes the positive and negative charges between objects.(A negative charged cloud to a positive charged earth surface, or vise-versa)

When a negative charged cloud approaches the area of a positive charged earth surface(A tree, light pole, radio antenna,house,ect)the arc ensues.The arc is at a very high fequency for a short duration of time,often obtaing voltages over 30,000V with 60,000 ampers of current.

Light poles are conductive and therfore low resistivity and thus as the electrons flow the neutralization doesn't produce a heat intense enough to create a fire. On the other hand a tree or house is made of wood and has a high resistivity, when electrons flow to neutralization through this medium, heat ensues, which can lead to fire.

Lightning is not looking for a conductive path, that is why trees get struck. You are no more likely to be struck by lightning if your holding a 6-foot golf club in the middle of an open field than if you were holding a 6-foot wood 2x4 in the same location. Because lighting strikes proximity.

Grounding Electrodes(GE) are utilized to connect metal parts of electrical equipment to the earth to LIMIT the voltage from lightning by providing a conductive, low resistant path for the disipation of the neutralizing current flow between the earth and the cloud. If the system is not connected to earth the elevated voltage that enters the system will travel through the system via metal raceways or cables, seeking a path to earth. The high voltage on the metal parts from lightning can result is electric shock and fires, as well as the destruction of electrical equipment.

So if lightning striks your exterior pole light and it does NOT have a ground rod, than your contention is that the lightning will travel UNDERGROUND through the branch circuit,(ignoring the bolted connection to the concrete base not to mention the rebar in the concrete base,6-feet under ground,) enter your building system to find your building systems Electrode system to dissipate the energy into the earth.

Lets say that is true, and we decide to put a ground rod at each pole. Does this ground rod ensure all the lightning is shunted to ground and no current will travel into the building via the branch circuit conductors?

The answer is NO, even if you ground rod dissipated 90%(which it doesn't) of the lightning into the earth and 10% went into your building via the branch conductor your still allowing 3,000V at 6,000ampers of current to enter your system. HOW IS THAT PROTECTING YOUR SYSTEM?

To limit and protect your building from the entrance of lightning, you must utilize Transient Voltage Surge Suppression (TVSS)to shunt the lightning to the earth before it ever has the chance to enter your system. You do this by providing isolation transformers for your exterior lighting circuit and installing TVSS on the Branch panel that feeds your Exterior lighting.

To conclude, to say that a ground rod at your pole lights protects your interior electrical from lightning is false. It doesn't protect any thing. 3,000V or 30,000V what is the difference when you electrical system is only rated at 208 or 480 volts.

If there is a puplication that proves this wrong, and actually shows that ground rods at exterior pole lights PROTECT your internal electrical system, Quote me chapter and verse of the article and I will be happy to review it. The problem is I do not beleive it exists.
 

bphgravity

Senior Member
Location
Florida
Re: pole bases once and for all

I hate to impose on some truely expert and well informed facts on this post. They are all very interesting. My first question is if we are not too sure if a lightning/ground rod installation actually does anything or not, what is the hurt of putting one in for the chance that it may work? They certainly can't harm the system in any way. I agree that lightning is not looking for a conductive path, but only a nuetralizing arc. My take is directing the opposite charged ions away from the building or equipment and to the charged area by means of a conductive path.

Let me explain. Say a cloud is overhead with a negative charge. Below is Earth and some tress and a building, all with a positve charge. With an effective lightning protection sytem, the positive charge Earth and building have a condutive path to the air. Without the lightning system, the lightning discharge can will happen along the building or at Earth. So the idea is not to give Lighnting an effective path to flow, but the charge of the earth a path to get to air before lightning gets to it. Does this make any sense? :confused: :confused:
 

roger deas

Member
Location
North_Carolina
Re: pole bases once and for all

Bryan your idea in theory makes some sense if there is any constant theory for lightning.

The problem is, whether lightning is a high freq ac charge, or a fast rise dc charge, it takes on an ac characteristic in that you can have a 60' flag pole next to a wooden building and the "arc" will actually span nails in the wooden building and never touch the pole.

Of course like I said in the beginning of my post, "if there is any constant theory for lightning" so, I don't really know what I'm talking about any more than anyone else does when it comes to lightning.

I'm sure there are those that know more than me. ;)

Roger
 

luke warmwater

Senior Member
Re: pole bases once and for all

On another note, I've opened hand holes to find PVC conduit, a ground rod, and NO EGC pulled from the panel. This is definately NOT the way to do it.
 

bennie

Esteemed Member
Re: pole bases once and for all

The loop impedance is likely too high to permit the operation of the breaker, in some cases.

A GFP breaker would trip at a lower current. The rod would facilitate this.

A tee tap, with an inline fuse at the pole, would also clear a fault upstream of the fuse.

The surface impedance, of the surrounding terrain, reduces touch potential.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: pole bases once and for all

Bennie,
The loop impedance is likely too high to permit the operation of the breaker, in some cases.
This would be a violation of 250.4(A)(5).

Don
 
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