lighiting poles ground rod

[tkb]

Re: lighiting poles ground rod

250.52(A)(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth,........

When a vapor barrier is under the footing, the footing is not in direct contact with the earth.

How about when they dig out for the fotting and then compact crushed stone for a base under the footing?
Is this in direct contact or do they mean virgin soil?
What if the footing is directly on ledge? Will it make a good concrete encased electrode?

 

[charlie tuna]

Re: lighiting poles ground rod

all,
please post any information where you witnessed, in your oppinion, an installation where you thought the installation of a ground rod at a pole base limited or prevented lightning damage..
i have replaced too many panels, breakers, time clocks and contactors feeding poles with ground rods to think they actually performed a function!!

 

[GENEM]

Re: lighiting poles ground rod

I believe the ground rod is actually to try to prevent the lightning from using the conductors as a path. The copper makes a much better conductor than concrete. Up here in the Rocky Mountains lightning is an everyday fact of life or death --just don't get hit.

 

[bphgravity]

Re: lighiting poles ground rod

Originally posted by GENEM:
I believe the ground rod is actually to try to prevent the lightning from using the conductors as a path. The copper makes a much better conductor than concrete...

The problem isn't the copper's resistance, its the resistance of the rod to the soil. The surface area of a ground rod is simply not large enough to be an effective conductor.

 

[GENEM]

Re: lighiting poles ground rod

The lightning is trying to get to ground--usually by the path of least resistance-any path provided which will allow the discharge of the energy with the least amount of damage is a plus. The lightning is a release of the positive and negative static charges built up by the weather system. I might be mistaken but most of that charge on the earth side is a surface charge, grounding tends to bleed that charge off making the chance of a lightning strike in that area less. I work at a site with many above ground tanks and pipe racks carrying flammable solvents. We are required to ground every tank at least twice and all racks and building steel to a ground grid with ground rods spaced throughout the site. Though we are one of the high points in the area, we have lightning strikes all around us but have never had one on site-- I hope and pray we don't or you probably won't hear from me again.

 

[Jhr]

Re: lighiting poles ground rod

all,
please post any information where you witnessed, in your oppinion, an installation where you thought the installation of a ground rod at a pole base limited or prevented lightning damage..
i have replaced too many panels, breakers, time clocks and contactors feeding poles with ground rods to think they actually performed a function!!

I'm with you, I thought ground rods were for grounding not for lightning protection. I don't see where a ground rod would be effective if a light pole was to take a direct hit. The pole would have some kinda damage, I've seen many lighting strikes to these big custom homes and the strike is either to the chimminey or the highest part of the roof .

 

[tom baker]

Re: lighiting poles ground rod

Its a myth that a ground rod will protect a luminare pole from damage in a lighting strike. If lighting hits the pole, the luminare is toast. Most likely the biggest reason we have ground rods at lighting poles is "the civil engineer drives the bus on traffic signal and roadway lighting jobs".
Lighting won't damage a concrete foundation either, as its a high frequency - high voltage effect, you can take what youve learned at 60 hz and apply to lighting.
Tom
International Municipal Signal Association representative to the Illumination Engineering Society and member of the Roadway Lighting Committee

 

[benaround]

Re: lighiting poles ground rod

Personally I feel that an Air Terminal at the top of the lighting pole would reduce damage/direct hits, by a significant amount.Lightning Protection does work,using parts made for the purpose,well,say no more--

frank

 

[hurk27]

Re: lighiting poles ground rod

Personally I feel that an Air Terminal at the top of the lighting pole would reduce damage/direct hits, by a significant amount.Lightning Protection does work,using parts made for the purpose,well,say no more--

Frank as long as you keep it a personal belief then you'll be ok.

Lightning follows more of the RF theory then it does the 60hz or DC, If a attachment point is in resonance to the frequency of a particular stroke then there is a good chance it will get struck.

By Genem: grounding tends to bleed that charge off making the chance of a lightning strike in that area less.

As for the grounding of the tanks and installing a grounding grid I would say don't bank on that lightning will never strike this place.
I have seen many tank farms not to far from here lite up by lightning, I have seen where they installed intercept wires high across the site which will defer the strikes away from the tanks just as Ufer used in protecting ammo storage bunkers, This creates a semi Faraday cage, But even it's not fool proof as lightning can still induce enough current across a Faraday cage to cause sparks between un-bonded metal on the other side of it.

I would say to go to this site : National Lightning Safety Institute (NLSI) Home Page.
And prepare to do some reading as it is one of the best sites on-line about lightning, There are too many myths on lightning that one needs to know the real truth about before making assumptions, And from this statement:

I hope and pray we don't or you probably won't hear from me again.

You can see where assumptions could cost a life.

 

[GENEM]

Re: lighiting poles ground rod

I,m stuck at the mercy of the engineers who say how to ground/bond. Heaven help me!!!

 

[benaround]

Re: lighiting poles ground rod

hurk27,

As long as you keep it personal ok. Actually it is what a 14 page report by NFPA instructs to do.They have over 100 years of documentation backing their words,I'm listening to them,personally.

frank

 

[charlie tuna]

Re: lighiting poles ground rod

if the ground rod at the pole is for reducing damage in the instance of a lightning strike(?) why aren't we required to follow the installation practices of lightning protection system installations like "no short radius cable bends"? seems to me that the lightning would jump off the conductor going to the average "pole located" ground rod??? any time i was involved in repair work concerning a lightning strike to a pole or parking lot situation, i would always inspect the grounding system at the poles and the service---i never witnessed anything abnormal? yet maybe the 12 circuit lighting contactor would be smoked and the cover blown off!!!

 

[wirenut1980]

Re: lighiting poles ground rod

I have always wondered that is ground rods are also used for lightning protection, that why their installations are not required to follow NFPA 780 requirements like a larger wire size than #6 AWG for the conductors for example. IMO, I don't think they do much for lightning protection.

 

[Jhr]

Re: lighiting poles ground rod

I have always wondered that is ground rods are also used for lightning protection, that why their installations are not required to follow NFPA 780 requirements like a larger wire size than #6 AWG for the conductors for example. IMO, I don't think they do much for lightning protection.

This is the second time I have seen this statement, and as I stated before I thought ground rods are for grounding not for lighting protection.

 

[benaround]

Re: lighiting poles ground rod

Jhr,

What kind of grounding are you talking about.

frank

 

[Jhr]

Re: lighiting poles ground rod

By Benaround: What kind of grounding are you talking about.

The kind that is in "NEC Art 250 Grounding and Bonding", or has that also become politically incorrect .

[ August 12, 2005, 08:16 PM: Message edited by: Jhr ]

 

[benaround]

Re: lighiting poles ground rod

Jhr,

That being said,250.4 A(1) is your answer.

frank

 

[Jhr]

Re: lighiting poles ground rod

That being said,250.4 A(1) is your answer.

That said IMO the NEC needs to rethink there wording, I have seen many lightning strikes and a lone ground rod was not very effective, reson been the structure sometimes has fire damage, structural damage, not to mention all the high priced electronics that are damaged, IMO ground rods are useless in a lightning strike :roll:

[ August 12, 2005, 09:25 PM: Message edited by: Jhr ]

 

[charlie tuna]

Re: lighiting poles ground rod

all,
was at a friend's home today and his house was hit by lightning this week. blew his low voltage yard light transformer apart --- tripped three gfic receptacles and they will not reset-- toasted his remote phone - and blew his t.v. cable in half. the point where it blew the t.v. cable in half was three feet from his service ground rod...????????????

 

[hurk27]

Re: lighiting poles ground rod

hurk27,

As long as you keep it personal ok. Actually it is what a 14 page report by NFPA instructs to do.They have over 100 years of documentation backing their words,I'm listening to them,personally.

frank

Doing something for even 100 years does not make it right. As new knowledge comes out all the time, it can mean they have been doing it wrong for a 100 years.
With lightning, It's still not fully understood and maybe for some time.
Grounding and bonding requirements in the NEC does not even start to cover what it take to protect a building. Not having a GEC over 25' long is one requirement the should be in the NEC as they did understand this in article 800 but didn't address this in 250?

This is why the NEC requirements are at best a very very?very?minimum for lightning protection!