# Purpose of ground rod



## swimmer (Mar 19, 2011)

Customers often inquire as to the purpose and value of ground rods.

*From research on the web, this is what I've found.*
1. Ground rod dissipates energy from lightening strike, on grounded surface, into ground.

2. Same as 1 but for a hot power line that somehow comes into contact with a grounded surface, of structure, or with the neutral / ground power line.

3. Surge on hot power line causes arc between hot buss bar and ground bar in service panel. Much energy is dissipated in this arc. Remainder of energy is dissipated into ground by rod.

*What I've experienced.*
Provides alternate, but limited, current path back to power company transformer when grounded conductor, between service panel and power company transformer, becomes severed. I've seen houses operate pretty normal under this condition until I unplugged everything, except for test loads, to exasperate the problem.

Does anyone know other purposes of the ground rod?
Does it help reduce noise on sensitive equipment?

Thanks


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## macmikeman (Jan 23, 2007)

Setting Lightning issues aside, the information gathered from the "web" about dissipating into the ground is false information.


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## bkmichael65 (Mar 25, 2013)

Ground rods and readily accesible GEC's provide a means of supporting a crack addiction here in Florida


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## backstay (Feb 3, 2011)

It gives a reference for your system so you don't have a voltage potential between the earth and your neutral.


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## macmikeman (Jan 23, 2007)

bkmichael65 said:


> Ground rods and readily accesible GEC's provide a means of supporting a crack addiction here in Florida


And how do the crack addicts get wealthy from extracting a microthin cladding of copper on a steel rod? Wait, I know how, Florida recycler's are dumb enough to think the rod is entirely copper, just like how the crack addicts do....


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## bkmichael65 (Mar 25, 2013)

Crackheads will steal any kind of metal they can sell. There was a guy in the next county stealing manhole covers awhile back and recyclers were paying him for them.


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## HARRY304E (Sep 15, 2010)

swimmer said:


> Customers often inquire as to the purpose and value of ground rods.
> 
> *From research on the web, this is what I've found.*
> 1. Ground rod dissipates energy from lightening strike, on grounded surface, into ground.
> ...


Swimmer read all of this..

http://forums.mikeholt.com/showthread.php?t=95495


"Driving a ground rod to ‘ground’ any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a ground rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A ground rod with 25 ohms to earth will allow almost five amps to escape the system into the earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this ground rod will be energized to 120V."


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## backstay (Feb 3, 2011)

macmikeman said:


> And how do the crack addicts get wealthy from extracting a microthin cladding of copper on a steel rod? Wait, I know how, Florida recycler's are dumb enough to think the rod is entirely copper, just like how the crack addicts do....


Maybe the recyclers "are" the crack addicts.


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## 220/221 (Sep 25, 2007)

I always tell people that ground rods/ufers give the lightning somewhere to go. :jester:


Which brings up the question, if lightning travels thru a ufer, wouldn't it possibly crack the **** out of the footing?


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## swimmer (Mar 19, 2011)

220/221 said:


> I always tell people that ground rods/ufers give the lightning somewhere to go. :jester:
> 
> 
> Which brings up the question, if lightning travels thru a ufer, wouldn't it possibly crack the **** out of the footing?


Yes, I've read that a lightning charged Ufer in a slab where moisture has penetrated can create steam can crack the slab.


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## brian john (Mar 11, 2007)

220/221 said:


> I always tell people that ground rods/ufers give the lightning somewhere to go. :jester:
> 
> 
> Which brings up the question, if lightning travels thru a ufer, wouldn't it possibly crack the **** out of the footing?


 
It cracks trees, so it seems possible but not sure if there are any documented cases, maybe with the large surface area in contact with the Earth the energy and temperature is limited somewhat?


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## Marcus (Mar 30, 2010)

backstay said:


> It gives a reference for your system so you don't have a voltage potential between the earth and your neutral.


Depending on the impedance of your earthing system & factors like distance from transformer, soil, cable & connections, there will always be potential difference between earth & neutral. The MEN system is a wonderful thing


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## Dennis Alwon (May 9, 2009)

swimmer said:


> *What I've experienced.*
> Provides alternate, but limited, current path back to power company transformer when grounded conductor, between service panel and power company transformer, becomes severed. I've seen houses operate pretty normal under this condition until I unplugged everything, except for test loads, to exasperate the problem.
> Thanks



I am not sure where you experienced this but a ground rod is highly unlikely to provide a path back to a transformer when the neutral is broken. I have never seen this. It is possible for current to travel back thru copper pipes that are connected thru a community metal piping system as long as the meter does not have a dielectric fitting.

The rod is pretty much for lightning and surges.


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## Big John (May 23, 2010)

Interesting timing: I just got in a big old argument with one of our engineers. We do a lot of ground resistance testing. Sometimes I can see the importance: Lightning protection systems and substation grounds where the earth is used to clear high-voltage faults.

In <600V systems, I think the testing is useless. Who cares if we have 5Ω grounds? Who's to say they're even gonna stay at 5Ω? And even if they do, what benefit does that even provide? 

I really think a lot of low voltage grounding is hocus pocus. I also blame you guys for giving me this opinion.


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## Mshea (Jan 17, 2011)

From the Canadian Electrical code

The object of grounding the electrical system and non-current-carrying metal parts is to connect the earth
to the equipotential plane, thereby minimizing any potential difference to earth.

The primary purpose is to maintain equipotential plane. It serves in high voltage contact to prevent voltage rise thus creating potential differences between 2 points. IE touch and step voltages. A high voltage contact includes lightning and a transformer failure too.​


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## brian john (Mar 11, 2007)

Mshea said:


> From the Canadian Electrical code
> 
> *The object of grounding the electrical system and non-current-carrying metal parts is to connect the earth
> to the equipotential plane, thereby minimizing any potential difference to earth.*
> ...


I agree connecting the metallic component, keeping at the earth potential under 600 VAC ewwwwww, not so sure it buys much.

Lightning and high voltage exposure.


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## Jlarson (Jun 28, 2009)

The purpose is to sell ground rods.


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## 220/221 (Sep 25, 2007)

They make good sturdy spindles for rolls of small thhn!!


I don't know how I ended up with so many short pieces though.


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## dronai (Apr 11, 2011)

220/221 said:


> They make good sturdy spindles for rolls of small thhn!!
> 
> 
> I don't know how I ended up with so many short pieces though.


I use emt bones for that. I would sell your spindles for beer money.


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## macmikeman (Jan 23, 2007)

Mshea said:


> From the Canadian Electrical code
> 
> The object of grounding the electrical system and non-current-carrying metal parts is to connect the earth
> to the equipotential plane, thereby minimizing any potential difference to earth.
> ...


All good in theory. All lacking in real time proof. I have been subject to step potential electrical shock before, and all the ground rods from the building system did nothing to reduce that. If anything , they promoted the problem. They allowed it to happen. I know how cows feel about "good grounding". Too bad this didn't happen in Canada, cause then I could have sued for misleading the public on the issue........... :laughing:


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## westom (Nov 12, 2011)

brian john said:


> It cracks trees, so it seems possible but not sure if there are any documented cases, ...


 Some see a tree cracked by lightning. Then assume lightning does that to all trees. Reality. Well over 90% of all trees struck by lightning have no appreciable indication.

Too many 'know' from observation. And forget to examine the maybe 99 other strikes that cause no tree damage. Much junk science is promoted by using this defective data collection method.

Ufer grounds only cause cracked concrete when improperly installed. Telco switching stations suffer about 100 surges with each storm. And no damage. Because an earth ground routinely earths (dissipates) that energy by connecting its current to distant charges (maybe miles away). Ufer grounds successfully protect switching centers (COs) and munitions dumps.

A ground measuring 25 ohms at a near zero current is not 25 ohms at higher currents. 

Among many purposes of earth ground is to eliminate a reason for decreased milk production in cows. Equipotential and conductivity summarize the many purposes of earth ground.


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## dmxtothemax (Jun 15, 2010)

swimmer said:


> Customers often inquire as to the purpose and value of ground rods.
> 
> *From research on the web, this is what I've found.*
> 1. Ground rod dissipates energy from lightening strike, on grounded surface, into ground.
> ...


The primary purpose of a ground rod is to provide a common reference
to stabilise the entire distrubution system.

They were primarally in this area in the era of swer systems.

But it also plays a part in many other things as you have summerised.


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## micromind (Aug 11, 2007)

Jlarson said:


> The purpose is to sell ground rods.


And to an even greater degree, they make life difficult for anyone who drives them into rocky soil, generally resulting in less respect for the code and those who enforce it.


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## Magnettica (Jan 23, 2007)

Ground rods are for new guys who thought they'd be putting in light bulbs all day.


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## Meadow (Jan 14, 2011)

Ground rods are probably there for utility reasons. But high voltage aside a low voltage system does well 99.99% of the time without a ground rod. Noise, harmonics and the rest are BS. Lightning yes they do help, but that's it.


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## dmxtothemax (Jun 15, 2010)

dmxtothemax said:


> The primary purpose of a ground rod is to provide a common reference
> to stabilise the entire distrubution system..


They were primarally used, in this area, in the era of swer systems.

But it also plays a part in many other things as you have summerised.


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## brian john (Mar 11, 2007)

westom said:


> *Some see a tree cracked by lightning. Then assume lightning does that to all trees*. Reality. Well over 90% of all trees struck by lightning have no appreciable indication.
> 
> d.



If it did it to ALL trees we'd live on a treeless planet.:blink::laughing:


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## Celtic (Nov 19, 2007)

brian john said:


> If it did it to ALL trees we'd live on a treeless planet.:blink::laughing:


...it'd be real hot too


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## ohmontherange (May 7, 2008)

westom said:


> Some see a tree cracked by lightning. Then assume lightning does that to all trees. Reality. Well over 90% of all trees struck by lightning have no appreciable indication.
> 
> Too many 'know' from observation. And forget to examine the maybe 99 other strikes that cause no tree damage. Much junk science is promoted by using this defective data collection method.
> 
> ...


I'm not sure where you got that number. It would depend on the number of cloud to ground strikes in proximity or direct strikes / induction to metallic conductors entering the facility. Geography is a factor - isokeraunic number or lightning days per year.

I do know that central offices, mobile swithing centers, etc have very stringent grounding / bonding practices.


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## drsparky (Nov 13, 2008)

Ground rods provide a path to ground for lightning and reference for the grid. Each ground rod is in parellel with hundreds if not thousands of others through the power companys transmition system.


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## 8V71 (Dec 23, 2011)

drsparky said:


> Ground rods provide a path to ground for lightning and reference for the grid. Each ground rod is in parellel with hundreds if not thousands of others through the power companys transmition system.


Short, sweet, and easy to understand. What's not to like! :thumbsup:


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## chicken steve (Mar 22, 2011)

westom said:


> A ground measuring 25 ohms at a near zero current is not 25 ohms at higher currents.
> 
> .


good point

adding to it would be soil conditions , as well as the fact that so few G rods are actually assessed for *R* during installation

~CS~


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## brian john (Mar 11, 2007)

chicken steve said:


> good point
> 
> adding to it would be soil conditions , as well as the fact that so few G rods are actually assessed for *R* during installation
> 
> ~CS~


Less than .0001% I would bet and that may be high.


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## Cletis (Aug 20, 2010)

To help people from dying in the shower while having relations grabbing plumbing and secret competitive plot against tvss companies for poor sales


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## hardworkingstiff (Jan 22, 2007)

Celtic said:


> ...it'd be real hot too


Oh no, that's junk science.


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## hardworkingstiff (Jan 22, 2007)

westom said:


> A ground measuring 25 ohms at a near zero current is not 25 ohms at higher currents.





chicken steve said:


> good point


I'd like to have more information on this. How does current change the resistance of the ground rod/earth connection?


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## Cletis (Aug 20, 2010)

Oh, and to get long life and corrosion resistance I hope you all are using 10 mil copper coated rods min driven 10ft per Ericko's findings from Bureau of Standards, Circular 579 (1957) and Field Testing of Electrical Ground Rods, Naval Civil Engineering laboratory (1970). I consider these findings worth their weight in gold and abide to them at all cost


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## swimmer (Mar 19, 2011)

220/221 said:


> They make good sturdy spindles for rolls of small thhn!!
> 
> 
> I don't know how I ended up with so many short pieces though.


Short pieces of ground rods? :laughing:


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## Cletis (Aug 20, 2010)

220/221 said:


> They make good sturdy spindles for rolls of small thhn!!
> 
> 
> I don't know how I ended up with so many short pieces though.


I had an inspector that wore steel toe boots and would walk up and give the top of rod a swift, hard kick and would know if you tried this around here. He busted all kinds of guys doing that.


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## 480sparky (Sep 20, 2007)

The true purpose of a ground rod is to give your apprentice something to do so you can go do something productive.


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## swimmer (Mar 19, 2011)

Dennis Alwon said:


> I am not sure where you experienced this but a ground rod is highly unlikely to provide a path back to a transformer when the neutral is broken. I have never seen this. It is possible for current to travel back thru copper pipes that are connected thru a community metal piping system as long as the meter does not have a dielectric fitting.
> 
> The rod is pretty much for lightning and surges.


A pipe network may very well have been the path since the break was upstream from the ground buss where cold water bond and the GEC were attached. 

If ground rods provide such terrible return paths then why was the Single Wire Earth Return system so effective?


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## swimmer (Mar 19, 2011)

hardworkingstiff said:


> I'd like to have more information on this. How does current change the resistance of the ground rod/earth connection?


I don't know if this is right but I just think of it as ampacity like any wire. With tiny currents you read zero voltage drop. With huge currents, you get a voltage drop. V/I = R


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## westom (Nov 12, 2011)

ohmontherange said:


> I'm not sure where you got that number. It would depend on the number of cloud to ground strikes in proximity or direct strikes / induction to metallic conductors entering the facility.


 Correct. Geology and items in the ground (ie intercontinental pipelines) can seriously affect that number. Strikes between two locations can vary significantly.

In the 1950s, telcos were preparing to upgrade to transistors. Bell researchers analyzed quality of their existing protection (earth ground). Studies in New Jersey, Georgia, and elsewhere demonstrated that COs suffer many surges with each thunderstorm. Protection is defined by earth ground. With minor exceptions, earthing installed in COs was sufficient to protect even transistors from direct lightning strikes. That electrode does the protection.

Critical are two words: equipotential and conductivity. Good earthing electrodes do both so that even direct lightning strikes to incoming wires cause no damage.


How does current change resistance? It is routine around you. Few items actually have linear resistance. Measure resistance of an incandescent light bulb. Then do the math. 120 volts squared divided by that resistance is how many watts? That watts number will be significantly different from a number on the box. Resistance (and therefore wattage) changes with changing current. In this example, resistance increases. In other examples (ie fluorescent and CFL bulbs, earth ground), resistance decreases.


In one house, the transformers neutral slowly failed. The homeowner saw and ignored bulbs changing intensity. And did not inspect his defective earth electrodes. Eventually that neutral failed. Without an essential earth electrode ground connection, current used a gas meter as an electrical conductor. Fortunately no one was home when the house exploded.


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## Marcus (Mar 30, 2010)

Dennis Alwon said:


> I am not sure where you experienced this but a ground rod is highly unlikely to provide a path back to a transformer when the neutral is broken. I have never seen this. It is possible for current to travel back thru copper pipes that are connected thru a community metal piping system as long as the meter does not have a dielectric fitting.
> 
> The rod is pretty much for lightning and surges.


In the event of a broken neutral, the return current would not flow through the ground all the way back to the star point of the transformer but would most likely take the path of least resistance & find its way back up through a neighbouring installation and back down the line through their (unbroken) neutral conductor. Or in our case down here, steel power poles have the service neutral bonded to the top of them, effectively giving another return path back.


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## drsparky (Nov 13, 2008)

westom said:


> Correct. Geology and items in the ground (ie intercontinental pipelines) can seriously affect that number. Strikes between two locations can vary significantly.
> 
> In the 1950s, telcos were preparing to upgrade to transistors. Bell researchers analyzed quality of their existing protection (earth ground). Studies in New Jersey, Georgia, and elsewhere demonstrated that COs suffer many surges with each thunderstorm. Protection is defined by earth ground. With minor exceptions, earthing installed in COs was sufficient to protect even transistors from direct lightning strikes. That electrode does the protection.
> 
> ...


The resistance of a filament is at operating temperature, not ambient temperature.


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## westom (Nov 12, 2011)

drsparky said:


> The resistance of a filament is at operating temperature, not ambient temperature.


 So you agree. Resistance is not linear as many assume. In fact, it varies significantly. In many devices (ie fluorescent bulbs, transistors, and even earth), resistance changes with electrical parameters. A constant resistance over many currents requires special design constraints that does not exist here.

What measures 25 ohms at milliamps is not 25 ohms at significantly higher currents. That 25 ohm number is a crude ballpark number. Even the NEC (safety code) does not define how it should be measured.

What are functions of an earth ground? In coal mines, also so that a mine explosion does not happen. But again, in every case, the underlying concept remains constant: conductivity and equipotential.


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## Big John (May 23, 2010)

swimmer said:


> ...If ground rods provide such terrible return paths then why was the Single Wire Earth Return system so effective?


 I don't have a solid understanding of SWER, but I think it works out that after a certain distance from the electrode system, the earth resistance drops off drastically, because you basically have an infinite number of parallel paths through the soil. 

So, if the electrode system is good enough to get over the initial high-resistance hump and make solid contact, the earth is a very good conductor. With distribution the voltages are often high enough to make it easy to overcome that resistance.

I dunno, maybe someone can clarify that?


drsparky said:


> The resistance of a filament is at operating temperature, not ambient temperature.


 I think that's what he was driving at, that maybe in a high current fault the impedance of an electrode increases significantly? Not sure if that's accurate or not. Electrode system resistance increases with temperature, but I don't know how quickly that would occur during a fault.


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## Wirenuting (Sep 12, 2010)

Ground rods were invented to Nail the soil to the earth.. 
If you don't use them you will have a floating ground... Right?


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## drsparky (Nov 13, 2008)

Wirenuting said:


> Ground rods were invented to Nail the soil to the earth..
> If you don't use them you will have a floating ground... Right?


The Navy uses a floating ground, except submarines.:jester:


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## Semi-Ret Electrician (Nov 10, 2011)

westom said:


> So you agree. Resistance is not linear as many assume. In fact, *it varies significantly*. In many devices (ie fluorescent *bulbs*, transistors, and even earth), resistance changes with electrical parameters. A constant resistance over many currents requires special design constraints that does not exist here.
> 
> What measures 25 ohms at milliamps is not 25 ohms at significantly higher currents. That 25 ohm number is a crude ballpark number. Even the NEC (safety code) does not define how it should be measured.
> 
> What are functions of an earth ground? In coal mines, also so that a mine explosion does not happen. But again, in every case, the underlying concept remains constant: conductivity and equipotential.


Because the resistance varies even with ambient temperature, I've heard an ordinary bulb can be used to measure temperature.


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## RIVETER (Sep 26, 2009)

The sole purpose of a ground rod on an electrical system is to take a larger than expected current because of a larger than expected voltage to EARTH. That is it. It isn't even mystical.


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## backstay (Feb 3, 2011)

RIVETER said:


> The sole purpose of a ground rod on an electrical system is to take a larger than expected current because of a larger than expected voltage to EARTH. That is it. It isn't even mystical.


So if I expected 10 amps but got 12, 2 go to the ground rod? How does that work?


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## someonespecial (Aug 31, 2012)

westom said:


> In one house, the transformers neutral slowly failed. The homeowner saw and ignored bulbs changing intensity. And did not inspect his defective earth electrodes. Eventually that neutral failed. Without an essential earth electrode ground connection, current used a gas meter as an electrical conductor. Fortunately no one was home when the house exploded.


Why would it just explode? I would think 3/4 black pipe would have excellent ampacity and natural gas is not conductive.


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## hardworkingstiff (Jan 22, 2007)

westom said:


> So you agree. Resistance is not linear as many assume. In fact, it varies significantly. In many devices (ie fluorescent bulbs, transistors, and even earth), resistance changes with electrical parameters. A constant resistance over many currents requires special design constraints that does not exist here.


We were talking about ground rods. I don't think it is an accurate comparison, light bulb filaments or CFLs to resistance in a ground rod.

How much resistance change would there be in that ground rod between 0 amps and 5 amps? I don't believe it would be significant. I don't understand why you are making a point about resistance change of the ground rod. Now, if you want to say the resistance changes because of moisture in the ground, then I think that has merit. But since a direct connection from a phase conductor (120V to neutral with the neutral grounded) to a ground rod that has it's reference to neutral removed would at best (at 25 ohms) be close to 5-amps, the resistance change in the ground rod would be pretty insignificant.


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## hardworkingstiff (Jan 22, 2007)

swimmer said:


> If ground rods provide such terrible return paths then why was the Single Wire Earth Return system so effective?


Probably because 25 ohms of resistance does not offer much restriction on a 19kVA voltage.


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## westom (Nov 12, 2011)

hardworkingstiff said:


> How much resistance change would there be in that ground rod between 0 amps and 5 amps? I don't believe it would be significant.


 Resistance does not change much between milliamps and 5 amps. But then it does not have to. Because the resulting voltage differences beneath a house is also trivial. Meaning 120 VAC does not exist between what a human hand and human foot touch.

Meanwhile, when that current is thousands, then soil is significantly more conductive. When earthing severe transients, soil has different parameters.

Is it near zero? No. We can never make soil sufficiently conductive. In some venues, better grounds such as Ufer are needed. To not only increase conductivity. But to also increase equipotential.

What happened when they ignored dimming lights and did not inspect their earth ground? Gaskets in the gas line eventually failed resulting in an explosion. Gas lines are electrically isolated so as to not conduct electricity. Had earthing existed, a significant voltage would not have damaged gaskets.


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## Meadow (Jan 14, 2011)

westom said:


> Resistance does not change much between milliamps and 5 amps. But then it does not have to. Because the resulting voltage differences beneath a house is also trivial. Meaning 120 VAC does not exist between what a human hand and human foot touch.
> 
> Meanwhile, when that current is thousands, then soil is significantly more conductive. When earthing severe transients, soil has different parameters.
> 
> ...


Gaskets as in the Teflon coating?


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## Meadow (Jan 14, 2011)

swimmer said:


> A pipe network may very well have been the path since the break was upstream from the ground buss where cold water bond and the GEC were attached.
> 
> If ground rods provide such terrible return paths then why was the Single Wire Earth Return system so effective?


SWER works well because it does not rely on a one or two 8ft ground rods, it relies on a mesh, often with roads driven well below 10ft. The depth and the multiple rods cut resistance down significantly. This of course is done at the other end as well. Doing such a thing on a less than 600 volt service would be financially impractical, costing probably the service itself. 



westom said:


> Resistance does not change much between milliamps and 5 amps. But then it does not have to. Because the resulting voltage differences beneath a house is also trivial. Meaning 120 VAC does not exist between what a human hand and human foot touch.
> 
> Meanwhile, when that current is thousands, then soil is significantly more conductive. When earthing severe transients, soil has different parameters.
> 
> ...


I get current generating heat and resistance going up, or higher voltage pushing more current through the same resistance, but how does a high voltage surge cause resistance to go down in a ground rod?


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## westom (Nov 12, 2011)

meadow said:


> I get current generating heat and resistance going up, or higher voltage pushing more current through the same resistance, but how does a high voltage surge cause resistance to go down in a ground rod?


 Resistance changes with different materials. How does resistance go to and remains closer to zero in low pressure inert gases such as a fluorescent bulb? Resistance so low that voltage across that bulb is maybe tens of volts. But when measured with a meter, resistance exceeds 10 megohms.


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## hardworkingstiff (Jan 22, 2007)

westom said:


> Resistance changes with different materials. How does resistance go to and remains closer to zero in low pressure inert gases such as a fluorescent bulb? Resistance so low that voltage across that bulb is maybe tens of volts. But when measured with a meter, resistance exceeds 10 megohms.


I give up, how?


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## brian john (Mar 11, 2007)

someonespecial said:


> Why would it just explode? I would think 3/4 black pipe would have excellent ampacity and natural gas is not conductive.


There has to be more than just the current on the pipe.

Most residentials have low KW usage, the neutral being even lower do single phase, so there has to be something else that lead to a bad connection or spark.


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## Big John (May 23, 2010)

westom said:


> Resistance changes with different materials. How does resistance go to and remains closer to zero in low pressure inert gases such as a fluorescent bulb...?


 Very different scenario. You're ionizing gas.

In an electrode system the only obvious change I know of is heating due to current flow causing evaporation of moisture. But on most low-voltage systems that can't clear faults, this is a non-issue, and I would say that high voltage systems that are designed to clear faults take that into account.


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## brian john (Mar 11, 2007)

Big John said:


> Very different scenario. You're ionizing gas.
> 
> In an electrode system the only obvious change I know of is heating due to current flow causing evaporation of moisture. But on most low-voltage systems that can't clear faults, this is a non-issue, and I would say that high voltage systems that are designed to clear faults take that into account.


Moisture content
Soil type
Temperature of the soil.


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## Semi-Ret Electrician (Nov 10, 2011)

Big John said:


> I don't have a solid understanding of SWER, but I think it works out that after a certain distance from the electrode system, the earth resistance drops off drastically, because you basically have an infinite number of parallel paths through the soil.
> 
> So, if the electrode system is good enough to get over the initial high-resistance hump and make solid contact, the earth is a very good conductor. With distribution the voltages are often high enough to make it easy to overcome that resistance.
> 
> I dunno, maybe someone can clarify that? I think that's what he was driving at, that maybe *in a high current fault the impedance of an electrode increases significantly*? Not sure if that's accurate or not. Electrode system resistance increases with temperature, but I don't know how quickly that would occur during a fault.


John, look at your avitar, IMO just the opposite occurs. Before the "fault" what was the resistance between two phases in dry air. Once the air is ionized that space becomes a very good conductor.

Same with a lightning bolt, welders arc, charred wiring and grounding electrodes to earth during a lightning strike.

The 25 ohm DC resistance from a GE to earth IMO depends on many factors including height of the water table & surface moisture, temperature & Ph of the soil, number & length of the electrodes etc.

During a strike DC resistance is only a part of the equation. Impedance play's a much greater part, even sharp turns and proximity to building structure of the GEC and EGC's is important. If a loop is placed in wiring in a grounded panel a portion of the lightning has been known to leap to the panel.

Even the distance between phase and neutral/grounded conductors, in panels & wiring devices, acts as mini-spark gaps during a strike, and helps suppress the damage. Just as the SPD's and every surge strip helps the cause.

What I don't know about this subject far exceeds what I do know.


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## swimmer (Mar 19, 2011)

westom said:


> Gas lines are electrically isolated so as to not conduct electricity.


Westcom, how do resolve your statement (above) with 250.104(B)?

*250.104(B*) Other Metal Piping. Where installed on or attached to a building or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used.....


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## chicken steve (Mar 22, 2011)

Wiki echos your points SRE....http://en.wikipedia.org/wiki/Lightning ~CS~


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## Big John (May 23, 2010)

Semi-Ret Electrician said:


> ...During a strike DC resistance is only a part of the equation. Impedance play's a much greater part, even sharp turns and proximity to building structure of the GEC and EGC's is important. If a loop is placed in wiring in a grounded panel a portion of the lightning has been known to leap to the panel....


 No argument. But the 25Ω number is the connection between the electrode itself and remote earth, not the total impedance of the elelctrode system. And it read to me like he was saying that earth impedance could rise during a fault.

I've got a pretty weak understanding of what actually happens in the earth around the electrode, but my gut says that impedance doesn't change much during a fault.


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## Semi-Ret Electrician (Nov 10, 2011)

John, one would think by now we would know so much about lightning we would harness it as an energy source.

BTW, have you ever wondered why lightning seems to be a much greater problem where there are fewer poco customers?

I suspect the more interconnected EC's, from each customer, the more poco likes it. They only have a ground rod every 100 ft, if that. Unfortunately, much of the neutral current returned to them is via earth.


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## Meadow (Jan 14, 2011)

Semi-Ret Electrician said:


> John, one would think by now we would know so much about lightning we would harness it as an energy source.
> 
> BTW, have you ever wondered why lightning seems to be a much greater problem where there are fewer poco customers?
> 
> I suspect the more interconnected EC's, from each customer, the more poco likes it. They only have a ground rod every 100 ft, if that. Unfortunately, much of the neutral current returned to them is via earth.


 
Much of what we know of grounding and bonding at services is influenced by the POCO. Said fact.


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## Meadow (Jan 14, 2011)

Big John said:


> No argument. But the 25Ω number is the connection between the electrode itself and remote earth, not the total impedance of the elelctrode system. And it read to me like he was saying that earth impedance could rise during a fault.
> 
> I've got a pretty weak understanding of what actually happens in the earth around the electrode, but my gut says that impedance doesn't change much during a fault.


 
Under fault conditions its not uncommon for resistance to gradually go up around the ground rod due to water evaporating from heat. Saw it once where a guy grounded his faulted welder through a ground rod. Soil was much dryer around the rod, guy couldn't figure out why he was still getting shocked.


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## ohmontherange (May 7, 2008)

Semi-Ret Electrician said:


> John, look at your avitar, IMO just the opposite occurs. Before the "fault" what was the resistance between two phases in dry air. *Once the air is ionized that space becomes a very good conductor.*
> 
> Same with a lightning bolt, welders arc, charred wiring and grounding electrodes to earth during a lightning strike.
> 
> ...


Correct. Ever experience a " brownout" during a lightning storm when a recloser operates? Lightning causes a flashover on the primary distribution which creates an ionized path for 60hz current to flow until the reclosure opens and disrupts the current. They are designed to clear non persistent faults or lock out after a few tries on a persistent fault resulting in an outage. 

There is a difference between 60HZ fault current and lightning induced transients the latter which can have extremely high potential, very fast risetime voltage / currents.

Low _impedance_ ground systems are designed with these parameters in mind. To provide a low impedance path to ground for these destructive over voltages / currents.

PANI grounding systems are common in telecom / data facilities for these reasons.

Not what you see in resi or common commercial applications.


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## Semi-Ret Electrician (Nov 10, 2011)

Good post Ohm.

http://www.spgs-ground.com/information/types-of-grounding-designs is also a good source.


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## chicken steve (Mar 22, 2011)

ohmontherange said:


> PANI grounding systems are common in telecom / data facilities for these reasons.
> 
> Not what you see in resi or common commercial applications.












very interesting Ohm 

so would this be an option for those _'high lightning concern_' resi installs?

mountaintop home?

big CB ant in the yard?

etc....?

~CS~


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## brian john (Mar 11, 2007)

chicken steve said:


> very interesting Ohm
> 
> so would this be an option for those _'high lightning concern_' resi installs?
> 
> ...


CS- Not the conductor bends are sweeping in lieu of a tight bend, tight bends are seen as an open by high voltage, high frequency events.


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## ohmontherange (May 7, 2008)

chicken steve said:


> very interesting Ohm
> 
> so would this be an option for those _'high lightning concern_' resi installs?
> 
> ...


Sure as long as your installation is code compliant. Question is do you think the customer is going to buy it?

These type systems may reek of overkill to some but the companies who use them are attempting to protect very expensive and vital infrastructure and provide for continuity of service under adverse conditions. Nothing is surefire but it provides another layer of protection...


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## brian john (Mar 11, 2007)

ohmontherange said:


> Sure as long as your installation is code compliant. Question is do you think the customer is going to buy it?
> 
> These type systems may reek of overkill to some but the companies who use them are attempting to protect very expensive and vital infrastructure and provide for continuity of service under adverse conditions. Nothing is surefire but it provides another layer of protection...


And take a direct hit of a high enough magnitude and/or duration and all bets are off. I have seen a few sites totally fried, EVERYTHING, including the ground connections, every insulator supporting the bare halo ground conductor that was mounted on a conductive surface had a major flash over.


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## Big John (May 23, 2010)

brian john said:


> And take a direct hit of a high enough magnitude and/or duration and all bets are off. I have seen a few sites totally fried, EVERYTHING, including the ground connections, every insulator supporting the bare halo ground conductor that was mounted on a conductive surface had a major flash over.


 I always wondered about that. I know these places have ridiculous grounding standards, but it still seemed incredible to me that these towers could take direct lightning strikes with no damage. That's a lot of energy to dissipate.


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## papaotis (Jun 8, 2013)

Semi-Ret Electrician said:


> John, look at your avitar, IMO just the opposite occurs. Before the "fault" what was the resistance between two phases in dry air. Once the air is ionized that space becomes a very good conductor.
> 
> Same with a lightning bolt, welders arc, charred wiring and grounding electrodes to earth during a lightning strike.
> 
> ...


 which goes back to my earlier post that electricity is stupid, it doesnt always follow the path its supposed to:no:


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## ohmontherange (May 7, 2008)

Big John said:


> I always wondered about that. I know these places have ridiculous grounding standards, but it still seemed incredible to me that these towers could take direct lightning strikes with no damage. That's a lot of energy to dissipate.


And that is the point. The electronics that do all the magic usually keep humming away...


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## brian john (Mar 11, 2007)

Big John said:


> I always wondered about that. I know these places have ridiculous grounding standards, but it still seemed incredible to me that these towers could take direct lightning strikes with no damage. That's a lot of energy to dissipate.


The one site took a direct hit on the tower, damaged the tower, blew holes in the COAX, fried all the equipment in the 7-11 next door, and the adjacent Comcast site lost over 1/2 their equipment.

This one site was hit 3 times in one year and the other two times sustained limited damage.


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## Dennis Alwon (May 9, 2009)

Drive a ground rod in the earth and don't attach it to the grounding electrode system. Now take a #12 wire and hook it to a 20 amp breaker and turn it on. What will happen?

Do you think the breaker will trip? In most cases the breaker will not trip unless you get less than 6 ohms. That is often impossible with a rod in most areas of the country. I really don't expect you to try it but I know someone who did it because they didn't believe it. They were very careful and drove the rod far from their home so no one would get hurt. He was amazed,

Unless you have incredibly conductive soil and you are near the transformer then the rod will not trip the breaker. The purpose of the rod is to minimizes the effects from lightning and surges.


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## Shockdoc (Mar 4, 2010)

Dennis Alwon said:


> Drive a ground rod in the earth and don't attach it to the grounding electrode system. Now take a #12 wire and hook it to a 20 amp breaker and turn it on. What will happen?
> 
> Do you think the breaker will trip? In most cases the breaker will not trip unless you get less than 6 ohms. That is often impossible with a rod in most areas of the country. I really don't expect you to try it but I know someone who did it because they didn't believe it. They were very careful and drove the rod far from their home so no one would get hurt. He was amazed,
> 
> Unless you have incredibly conductive soil and you are near the transformer then the rod will not trip the breaker. The purpose of the rod is to minimizes the effects from lightning and surges.


Would a 100' + well casing act as a better ground that the rod, would the NEC recognize it as one?


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## Dennis Alwon (May 9, 2009)

IMO it would be better than a rod and I believe the well casing would qualify since 3/4" rigid is satisfactory-- That does not mean it will carry a neutral load of a building. Even if it did that is not it's function


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## ohmontherange (May 7, 2008)

Typical MGB installation in a small hut and some of the equipment it is meant to protect.

This building has a 2/0 CU perimiter ground ring.


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## kevink1955 (Apr 25, 2012)

We drive 30 foot rods for tower grounding and I once tryed to run a 3/8" drill using a rod as the neutral. The drill ran about 3/4 speed but had no power at all. I would have to guess it was good for about 1/2 amp at 120V.

Also these 30 foot rods are in sandy soil with at least 20' of them in the water table

See my Thanks LIPA thread, while I have 20 amps on the water pipe ground, I have nothing on the GEC (1 8' rod), or at least not readable on a 6a amprobe scale.


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## ceb58 (Feb 14, 2009)

brian john said:


> It cracks trees, so it seems possible but not sure if there are any documented cases, maybe with the large surface area in contact with the Earth the energy and temperature is limited somewhat?


We have had direct strikes on our towers that blew fist size chunks of concrete out.


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## piperunner (Aug 22, 2009)

Well i have seen it hit first hand a few times in Florida we have more strikes then any other state in the USA. In the summer its common to see it twice a week with rain or with out rain . Ive have seen lighting strike down during a sunny day in florida .

Story time we were doing a state prison project a little rain that day lightning hit a 50 foot concrete lighting pole it took off 5 feet of the top .We could not find one piece of the fixture that was on top vaporize to say the least .

This pole was 180 feet from the relay cabinet it burnt the wire which was 6 wire 3 conductor all the way back to the surge arrestor junction box plus the pole arrestor was vapor history .

Ground rod the 6 wire ground was gone the ground clamp gone 5 inches of ground rod gone because we pulled it back up to see .

This was a direct hit on the pole . 


Once standing in a electrical room on another project the crane was hit this was a 250 foot topped out tower crane . 

The ground system which was tied to everything in the building was completed guess it did its job but a fire ball came out of the conduits from underground and for that one second we all looked at each other and didnt know what the hell happened .

We only found out about the strike later thats when we knew what the hell happen . 

From what i have read lightning is not 60 cycles its a high frequency 
its mega volts and mega power . 

And its my thought that nothing can help when its a direct hit your done cooked its over Rod or no Rod .:laughing:

One of our electricians playing golf here in sunny Florida can tell you whats its like he was struck play golf and lived . But the guys with him not holding a club didnt get hit go figure .


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## brian john (Mar 11, 2007)

piperunner said:


> Well i have seen it hit first hand a few times in Florida we have more strikes then any other state in the USA. In the summer its common to see it twice a week with rain or with out rain . Ive have seen lighting strike down during a sunny day in florida .
> 
> .



From the Observer News

Florida leads the nation in deaths caused by lightning. The reasons for that are straightforward – Florida has both a high population and typically a large amount of lightning. In Hillsborough County, 32 people were killed by lightning between 1959 and 2003 – a number matched only by Miami-Dade County.

Only South and Central America, tropical Africa and Asia tend to have more lightning than Florida. Rwanda in Africa is generally considered to be the lightning capital of the world. But that is a fine distinction as Florida – and more specifically Hillsborough County – is thought to be the lightning capital of the U.S.

In many ways it is a matter of being in the right place at the right time. The right place, of course, is indoors away from things that draw lightning. When thunder is heard and lightning is visible, many experts recommend that people seek shelter inside of a home or vehicle. Trees and bodies of water – even canals – are considered dangerous. The "right time" is problematic as most lightning strikes occur in the month of July – a time when school is out and more people are out of doors. As a result, teenage boys tend to be the most likely victims, followed by people in the 30s and 20s, respectively.


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## RIVETER (Sep 26, 2009)

backstay said:


> So if I expected 10 amps but got 12, 2 go to the ground rod? How does that work?


In actuality you really hope not to have to use your grounding electrode. In that case it really would not be expected; It would be UN-anticipated.


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## RIVETER (Sep 26, 2009)

brian john said:


> The one site took a direct hit on the tower, damaged the tower, blew holes in the COAX, fried all the equipment in the 7-11 next door, and the adjacent Comcast site lost over 1/2 their equipment.
> 
> This one site was hit 3 times in one year and the other two times sustained limited damage.


I have never done tower work but was wondering why they could not place orbs, verses lightning rods at the top in order for the neg ions, or positive, depending on your belief, to NOT accumulate and the strike might possibly go to an adjacent tree or just to the ground. I guess they would not need a rod because of the structure, itself.


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## brian john (Mar 11, 2007)

RIVETER said:


> I have never done tower work but was wondering why they could not place orbs, verses lightning rods at the top in order for the neg ions, or positive, depending on your belief, to NOT accumulate and the strike might possibly go to an adjacent tree or just to the ground.


Because these negative ion have never been proved and generally are considered to be equal to Power Savers. VOODOO...

I can't locate the article I was lookng for regarding these.


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## RIVETER (Sep 26, 2009)

brian john said:


> Because these negative ion have never been proved and generally are considered to be equal to Power Savers. VOODOO...
> 
> I can't locate the article I was lookng for regarding these.


So you are saying that lightning arresters...verses lightning rods is unproven technology?


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## ohmontherange (May 7, 2008)

RIVETER said:


> So you are saying that lightning arresters...verses lightning rods is unproven technology?


Are you referring to a lightning deterrrent system?


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## brian john (Mar 11, 2007)

ohmontherange said:


> Are you referring to a lightning deterrrent system?


I beleve so.


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## Semi-Ret Electrician (Nov 10, 2011)

brian john said:


> And take a direct hit of a high enough magnitude and/or duration and all bets are off. I have seen a few sites totally fried, EVERYTHING, including the ground connections, every insulator supporting the bare halo ground conductor that was mounted on a conductive surface had a major flash over.


Very true Brian.
Lightning is sort of like a tornado if it's got your name on it ...all bets sure are off.

I noticed they cut about a foot of wire out of the halo, I suppose so that it's no longer a "pick-up coil". And, they're no longer bare wire.

Stong argument not to have a ground "ring" outside. Radials to a single point, IMO, are the way to go.


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## RIVETER (Sep 26, 2009)

ohmontherange said:


> Are you referring to a lightning deterrrent system?


Yes, in a way. The bottom line is that lightning does not say "I am going to earth, and that tree looks like a good place". The strike happens over time from an accumulation of the opposite charges and the resultant voltage is sufficient enough to ionize the path in between each other and the closest thing to earth which is the only way it can dissipate itself. It is my understanding that there are devices such as orbs that do not allow an accumulation of a charge but I am not in that business. I DO, however, have a power saver.


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## ohmontherange (May 7, 2008)

RIVETER said:


> Yes, in a way. The bottom line is that lightning does not say "I am going to earth, and that tree looks like a good place". The strike happens over time from an accumulation of the opposite charges and the resultant voltage is sufficient enough to ionize the path in between each other and the closest thing to earth which is the only way it can dissipate itself. It is my understand that there are devices such as orbs that do not allow an accumlation of a charge but I am not in that business. I DO, however, have a power saver.


I have seen dissipation arrays that were installed on top of towers. I don't know if they work or not.

I think the long and short of this thread is a low impedance ground and solid bonding (equipotential ground plane) in critical facilities will reduce the risk to an acceptable level.

I do work in carrier facilities and this is common practice and has been for a long time. 

I have copies of Telcordia standards as well as certain entities grounding DOC's which are confidential. But they are all based on the same principles.

Google Telcordia general requirements or even USDA RUS requirements (I know - you're thinking what the hell does the USDA have to do with grounding telecom installations)


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## RIVETER (Sep 26, 2009)

ohmontherange said:


> I have seen dissipation arrays that were installed on top of towers. I don't know if they work or not.
> 
> I think the long and short of this thread is a low impedance ground and solid bonding (equipotential ground plane) in critical facilities will reduce the risk to an acceptable level.
> 
> ...


Probably the same reason that they regulate Ferris wheels and roller coasters here in Kentucky.


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## Semi-Ret Electrician (Nov 10, 2011)

I was asked to provide a ground system on a mountaintop for a future celltower. Had to be <1 ohm

One rod tested >600 ohms. So, the site was passed over.

Since then, I can almost look at the soil and predict how it will test.

IAEI did a ground rod study all over the US and almost none achieved <25 ohms. So, drive the second one and move on.


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## RIVETER (Sep 26, 2009)

Semi-Ret Electrician said:


> I was asked to provide a ground system on a mountaintop for a future celltower. Had to be <1 ohm
> 
> One rod tested >600 ohms. So, the site was passed over.
> 
> ...


Where were your test points...from the electrode, etc. to where?


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## Semi-Ret Electrician (Nov 10, 2011)

RIVETER said:


> Where were your test points...from the electrode, etc. to where?


I have a three point tester. Where I drive two spikes at a distance from the rod being tested.


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## westom (Nov 12, 2011)

So many posts based in speculation, insufficient education, or confusion. Missing are well proven facts from over 100 years ago. And always defined by numbers. 

For example how does a surge incoming to an appliance create damage when an outgoing path to earth does not exist? It doesn't. And yet many know a surge was incoming on a cable ONLY because that cable input was damaged. An example of junk science reasoning.

A 200 watt transmitter connects to a long wire antenna. Touch one part of that copper wire to feel no voltage. Touch another part to be shocked by over 100 volts. Why two completely different voltages on the same wire? Those who don't know have no business making recommendations. Unfortunately, many who do not know how electricity works will even post accusations and speculation to avoid a fundamental fact. Knowledge was from advertising and popular myths; not from science. A statement not tempered by numbers is probably a lie.

Concepts such as impedance and E-M field theory apply. Knowledge without numbers is best called junk science. A majority never learn that well proven principle. 

Surges are not dumb. When damage happens, a misguided human is the reason for that damage. We thought we got it right everytime. And then the exception occurs. Lightning found a destructive path to earth we never knew. Well proven science discovers why we humans made a mistake. Concepts did not change. Either electricity connects harmlessly to earth. Or a human mistake connected that current to earth destructively via appliances. Some examples of damage averted when earthing is properly installed - exceeds code.

Why can two completely different voltages exist on the same copper wire? A concept taught in basic EM Fields. And that defines some purposes of the earth ground rod.

Keep reality in perspective. Electricians are not taught concepts that explain two completely different voltages on the same wire. Code discusses 60 hertz electricity. Code does not discuss different functions of an earth ground rod.

Question is purpose of a ground rod. It does human safety (defined by code). It does transistor safety (defined by other electrical concepts). It does other functions. How well? Underlying factor common is defined by two words - conductivity and equipotential. Concepts that explain why transistor protection requires a single point earth ground. And a low impedance (ie 'less than 10 foot') connection, have no sharp bends, no splices, and separated from other non-grounding wires. Where does code discuss any of this? It doesn't. Because code is only about human safety. Earth also for purposes not addressed by code.


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## bkmichael65 (Mar 25, 2013)

............


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## bobelectric (Feb 24, 2007)

Celtic said:


> ...it'd be real hot too


 Then, we can say "Ground Rods cause Global Warming."


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## uconduit (Jun 6, 2012)

Vincent3elly said:


> Ground rods and readily accesible GEC's provide a means of supporting a crack addiction here in Florida


Is the kind of copper that magnets stick to worth more????


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## chicken steve (Mar 22, 2011)

westom said:


> > Where does code discuss any of this? It doesn't.
> 
> 
> NFPA70 doesn't discuss theory, I don't know if NFPA780 addresses any of the conceptual points you've made
> ...


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## Big John (May 23, 2010)

westom said:


> ...Electricians are not taught concepts that explain two completely different voltages on the same wire. Code discusses 60 hertz electricity. Code does not discuss different functions of an earth ground rod....


 Because for the vast majority of electricians the rods are not installed primarily for lightning protection. That was already addressed early on in this thread: They're providing a system voltage reference and the NEC doesn't particularly care if they're 5Ω or 5,000Ω. 

There is a whole different field of lightning protection that requires separate training and certification, and the installations are drastically different than the grounding electrode systems needed in 99% of buildings.


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## chicken steve (Mar 22, 2011)

Yeah, but those lightning guys are like druids John....~CS~


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## chicken steve (Mar 22, 2011)

brian john said:


> CS- Not the conductor bends are sweeping in lieu of a tight bend, tight bends are seen as an open by high voltage, high frequency events.


Because higher hz has a skin effect, heavier charges seek straighter lines?

This opens a whole new realm of electrical theory , when we get outta the 120-480V 60HZ we're used to calculating within.....~CS~


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## chicken steve (Mar 22, 2011)

Semi-Ret Electrician said:


> I have a three point tester. Where I drive two spikes at a distance from the rod being tested.


Interesting

so would this reveal the 'step potential' we're always reading about SRE?

~CS~


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## piperunner (Aug 22, 2009)

brian john said:


> From the Observer News
> 
> Florida leads the nation in deaths caused by lightning. The reasons for that are straightforward – Florida has both a high population and typically a large amount of lightning. In Hillsborough County, 32 people were killed by lightning between 1959 and 2003 – a number matched only by Miami-Dade County.
> 
> ...


Well you are correct Brian you must be in the right place at the right time . There is a place in Florida that actually well check this out . I dont think a surge arrestor would help this or a ground rod LOL. They actually play with lightning in Gainsville Florida


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## Semi-Ret Electrician (Nov 10, 2011)

chicken steve said:


> Interesting
> 
> so would this reveal the 'step potential' we're always reading about SRE?
> 
> ~CS~


Theory of the 3 point system can be found at: 

http://www.esgroundingsolutions.com...-induced-frequency-ground-resistance-test.php

CS, I believe it's more a test of how effective the ground rod is in a particular soil. 

IMO, there will always be step potential around a ground rod, equipotential grid etc. If you have a downed 1000V line 100 ft from a ground rod I would expect to read about 500V from the rod to a point 50 ft in-between.

This assumes both the downed line and the ground rod both have the same earth to electrode resistance. And, the same soil conditions exist in-between.

Which is why one should take small steps if trapped in-between. 

My tester is an Ideal/Sperry mod 4105 and does not require as much thought, as talked about above.


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## RIVETER (Sep 26, 2009)

Semi-Ret Electrician said:


> I have a three point tester. Where I drive two spikes at a distance from the rod being tested.


Okay, then you are talking "Fall of potential". How far apart? How can you be sure of the result if you were even ten feet away with your rods? It seems to me to be arbitrary.


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## RIVETER (Sep 26, 2009)

westom said:


> So many posts based in speculation, insufficient education, or confusion. Missing are well proven facts from over 100 years ago. And always defined by numbers.
> 
> For example how does a surge incoming to an appliance create damage when an outgoing path to earth does not exist? It doesn't. And yet many know a surge was incoming on a cable ONLY because that cable input was damaged. An example of junk science reasoning.
> 
> ...


Wow! You said a lot, and you DO sound reasonably educated. Sit back for a second and think. Lightning rods...electrodes are not intended for human safety. They are intended for the "as quick as possible" path for a current that was not intended on that electrical system. Don't get me wrong . If a person is drunk inside a structure and a rod dissipates an abberrant current to earth he make wake up in the morning.


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## Semi-Ret Electrician (Nov 10, 2011)

RIVETER said:


> Okay, then you are talking "Fall of potential". How far apart? How can you be sure of the result if you were even ten feet away with your rods? It seems to me to be arbitrary.


The rod being tested is 20m from the last "spike". Current is imposed between these points.

Measurement is taken between the rod being tested and another "spike" half way between the first two. 

The digital meter calculates the driven rod's resistance.


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## RIVETER (Sep 26, 2009)

Big John said:


> Because for the vast majority of electricians the rods are not installed primarily for lightning protection. That was already addressed early on in this thread: They're providing a system voltage reference and the NEC doesn't particularly care if they're 5Ω or 5,000Ω.
> 
> There is a whole different field of lightning protection that requires separate training and certification, and the installations are drastically different than the grounding electrode systems needed in 99% of buildings.


I am not sure that I agree with you. A transformer does not need a ground reference in order to supply the utilization voltage for the devices that utilize that particular voltage. All electrical devices operate because of a potential difference in voltage. It should never rely on ground unless a fault occurs... and then only if the common is attached to ground.


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## RIVETER (Sep 26, 2009)

Semi-Ret Electrician said:


> The rod being tested is 20m from the last "spike". Current is imposed between these points.
> 
> Measurement is taken between the rod being tested and another "spike" half way between the first two.
> 
> The digital meter calculates the driven rod's resistance.


Are you saying that if you don't get the correct...or close resistance then a rod will have to be driven 60 feet away, and then call that good enough?


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## Semi-Ret Electrician (Nov 10, 2011)

RIVETER said:


> I am not sure that I agree with you. A transformer does not need a ground reference in order to supply the utilization voltage for the devices that utilize that particular voltage. All electrical devices operate because of a potential difference in voltage. It should never rely on ground unless a fault occurs... and then only if the common is attached to ground.


In an EPRI meeting it was disclosed that up to 60% of all neutral current back to the POCO is via earth.

Hard to get them to admit that in print.


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## RIVETER (Sep 26, 2009)

Semi-Ret Electrician said:


> In an EPRI meeting it was disclosed that up to 60% of all neutral current back to the POCO is via earth.
> 
> Hard to get them to admit that in print.


They are incorrect.


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## Semi-Ret Electrician (Nov 10, 2011)

RIVETER said:


> Are you saying that if you don't get the correct...or close resistance then a rod will have to be driven 60 feet away, and then call that good enough?


According to the NEC if you measure <25 ohms on the first rod you don't have to drive a second. Which I've done many times.

If you don't use an earth tester, just drive two. Which I usually do.

If it's a cell tower, telco, TV, Radio etc. NEC hardly applies, they like <1 ohm.


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## RIVETER (Sep 26, 2009)

Semi-Ret Electrician said:


> According to the NEC if you measure <25 ohms on the first rod you don't have to drive a second. Which I've done many times.
> 
> If you don't use an earth tester, just drive two. Which I usually do.
> 
> If it's a cell tower, telco, TV, Radio etc. NEC hardly applies, they like <1 ohm.


Still...60 feet away???


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## Semi-Ret Electrician (Nov 10, 2011)

RIVETER said:


> They are incorrect.


If you say so, but it would sure explain why farmers are having so much trouble with step potential.


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## dmxtothemax (Jun 15, 2010)

Dennis Alwon said:


> but a ground rod is highly unlikely to provide a path back to a transformer when the neutral is broken.


Quite wrong my friend !

In most cases the earth will provide a return path to the trannys.

In exceptional cases, if the ground is very dry, then it might not be so effective,


But it is a return path.


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## hardworkingstiff (Jan 22, 2007)

dmxtothemax said:


> Quite wrong my friend !
> 
> In most cases the earth will provide a return path to the trannys.
> 
> ...


A path with high resistance. The NEC seems to recognize 25 ohms as a reasonable resistance to ground. So, in a service with a grounded conductor and the ungrounded conductors operating at 120V to the grounded conductor we have the following path back to the tranny through the earth ground.

120/25= 4.8 amps. 

That is not sufficient enough to trip any breaker we use. So, based on that best case scenario (25 ohms is probably best case), the earth grounding does not provide a reasonable path for current flow.


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## chicken steve (Mar 22, 2011)

Semi-Ret Electrician said:


> Theory of the 3 point system can be found at:
> 
> http://www.esgroundingsolutions.com...-induced-frequency-ground-resistance-test.php
> 
> ...



grand link (with options) & explanation SRE :thumbsup: 

and i can recall having a similar conversation about _step potential_ decades ago with firemen who would roar up onto the scene of downed HV wires

that , and trying to impart the idea that rubber , at certain voltages, is merely dielectric 

~CS~


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## Semi-Ret Electrician (Nov 10, 2011)

hardworkingstiff said:


> A path with high resistance. The NEC seems to recognize 25 ohms as a reasonable resistance to ground. So, in a service with a grounded conductor and the ungrounded conductors operating at 120V to the grounded conductor we have the following path back to the tranny through the earth ground.
> 
> 120/25= 4.8 amps.
> 
> That is not sufficient enough to trip any breaker we use. So, based on that best case scenario (25 ohms is probably best case), the earth grounding does not provide a reasonable path for current flow.


I think everyone agrees such a situation would not operate the OCP or go un-noticed or be the only path back to POCO.

But it could be one of many paths and 120V at 4.8A divided between your ground rod(s) and the ones at the poles and your neighbors rods means a lot of earth could be energized.

Last week I had a situation where people were shocked touching a hose connection with bare feet. When I put a voltmeter on the hose connection and stuck it in the ground a few feet away I read over 60V. 

The house had un-grounded wiring and water lines, and a faulty water heater, which was easily found in minutes by monitoring the the voltmeter and turning breakers on and off.


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