# Useless 8ft Ground Rods



## BBQ (Nov 16, 2010)

Cletis said:


> 1 - 8ft 1/2 ground rod is basically useless. The national avg (avg may vary location, seasonal) is around 40 ohms.
> 
> And by a quick ohms law eq. that would be
> 
> ...



I think you are wasting your time, drive two 1/2" x 8' rods 6' apart and connect them to the service with 6 AWG and call it a day. And only if there is no concrete encased electrode available.





> *250.4(A)(5) Effective Ground-Fault Current Path.* Electrical equipment
> and wiring and other electrically conductive material
> likely to become energized shall be installed in a manner that
> creates a low-impedance circuit facilitating the operation of
> ...


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## Cletis (Aug 20, 2010)

*6 and coupling*

I heard 6ft is bad. 12 is way better? 

good idea on coupling the rods. Are 2 x 8ft rods drove 16ft better than 2 - 8 ft rods 6ft apart or 2 -10 ft rods set 12 feet apart ??

Which one is better and creates lower resistance ?


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## rexowner (Apr 12, 2008)

I guess you are posting this an an exercise in pulling someone's chain since
you should know that faults go back to the source, not to "ground".
Staying in the fantasy world for a second, what if the load were 50amp
or 100amps - breaker no trip - also, what's the resistance back to the
source?

Ignoring the fact that your basic premise is incorrect, from what little
information you give, your math seems to be wrong as well. If an
8 foot ground rod were 40 ohms, since resistance should be proportional
to length, a 10 foot of the same diameter would be 32 ohms. Since surface
area is directly proportional to diameter (you must have used the square
or something else wrong), going to 5/8 from 1/2 would
bring this down to 25.6ohms. Two in parallel - 12.8 ohms.

Since your math is wrong, along with the premise, IMO the idea does not
make a whole lot of sense.


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## Cletis (Aug 20, 2010)

*?*



rexowner said:


> I guess you are posting this an an exercise in pulling someone's chain since
> you should know that faults go back to the source, not to "ground".
> Staying in the fantasy world for a second, what if the load were 50amp
> or 100amps - breaker no trip - also, what's the resistance back to the
> ...


Your operating on the premise that ground faults travel "ONLY" through the neutral (grounded conductor) to transformer back to breaker than trippy. That's a bad assumption because some of the currect "DOES" travel through ground back to transformer. And then there is typical lighting surges and static problems as well why is needs to be real low. ????


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## rexowner (Apr 12, 2008)

Cletis said:


> Your operating on the premise that ground faults travel "ONLY" through the neutral (grounded conductor) to transformer back to breaker than trippy.


Umm, no, current will take all available paths. You are "ass"uming what
I am thinking, and as you know "ass"uming often leads to misunderstanding.



> That's a bad assumption because some of the currect "DOES" travel through ground back to transformer.


Yep.



> And then there is typical lighting surges and static problems as well why is needs to be real low. ????


You will be just fine with two ground rods with static, and if lightning strikes
your electrical system, two ground rods will probably not prevent 
severe damage.


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## erics37 (May 7, 2009)

Cletis said:


> Your operating on the premise that ground faults travel "ONLY" through the neutral (grounded conductor) to transformer back to breaker than trippy. That's a bad assumption because some of the currect "DOES" travel through ground back to transformer. And then there is typical lighting surges and static problems as well why is needs to be real low. ????


I think Brian John nailed you on this yesterday by informing you that in his vast experience, he would consider the amount of current travelling through earth back to the transformer ground (in a properly wired system of course) to be almost negligible.


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## Cletis (Aug 20, 2010)

*Debated*



erics37 said:


> I think Brian John nailed you on this yesterday by informing you that in his vast experience, he would consider the amount of current travelling through earth back to the transformer ground (in a properly wired system of course) to be almost negligible.


Well, the percentages can be debated whether it's 1% to 99% or 10% to 90% but in any case it's probably somewhere in middle. You also have to account for rusty carpola meters with bad neutral connections, service drops high resistance connections and possibly high resistance poco transformer connections (which is hard to believe) which all add to returning more current via ground when a fault actually occurs.


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## Cletis (Aug 20, 2010)

*more*

Also, I"m not doubting B.J's findings at all. But, I have another reliable good source who has a bit higher avg. Maybe B.J can chime in but when were the test done (winter, summer,fall,etc..), after a rain, in new england, in the sahara dessert, in commercial, residential, industrial, etc....lot's of factors is all i'm sayin

Just sayin


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## BBQ (Nov 16, 2010)

Make sure the main bonding jumper is in place and sleep well.


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## chicken steve (Mar 22, 2011)

Cletis said:


> I hear through the grapevine and Tom that driving 1 - 8ft 1/2 ground rod is basically useless. The national avg (avg may vary location, seasonal) is around 40 ohms.
> 
> And by a quick ohms law eq. that would be
> 
> ...


120,000 volts of lightning /40 ohms of rod(s) = 3000Amps


~CS~


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## Cletis (Aug 20, 2010)

*120k*

how bout 120k 

with 0.5 ohm grounding system

120,000 = I (0.5)

240k amps


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## BBQ (Nov 16, 2010)

Average lightning bolt 5 miles long.

Makes it through 5 miles of high impedance air, I doubt a ground rod one way or the other is going to make much difference.


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## MDShunk (Jan 7, 2007)

Even if you had a very low resistance ground rod to earth, how far away is the PoCo's transformer from those rods, and how good is their butt ground or padmount rod ground reference? 

If anyone in their right mind is putting real effort into getting low earth ground references for the purposes of fault clearing, they're wasting their time. Consider it for only re-directing some of a lightning strike to a location outside of the structure or _maybe_ clearing a primary to secondary fault a few cycles quicker.


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## BuzzKill (Oct 27, 2008)

exactly... lightning only, dude; that's all they are for.


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## Meadow (Jan 14, 2011)

MDShunk said:


> Even if you had a very low resistance ground rod to earth, how far away is the PoCo's transformer from those rods, and how good is their butt ground or padmount rod ground reference?
> 
> If anyone in their right mind is putting real effort into getting low earth ground references for the purposes of fault clearing, they're wasting their time. Consider it for only re-directing some of a lightning strike to a location outside of the structure or _maybe_ clearing a primary to secondary fault a few cycles quicker.


Isnt another purpose of a ground rod to bring the soil at the same or near same potential as the ground and neutral. ie, some one using a drill thats grounded outside will be of similar potential as everything else around him or am I missing something?


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## chicken steve (Mar 22, 2011)

MDShunk said:


> Even if you had a very low resistance ground rod to earth, how far away is the PoCo's transformer from those rods, and how good is their butt ground or padmount rod ground reference?
> 
> If anyone in their right mind is putting real effort into getting low earth ground references for the purposes of fault clearing, they're wasting their time. Consider it for only re-directing some of a lightning strike to a location outside of the structure or _maybe_ clearing a primary to secondary fault a few cycles quicker.


perhaps it's not the ohmic value that's as important then

i'm told (by the 780 guys) a GEC installed in straighter and shorter lines mitigates the heavy charge (or discharge) of lightning better

~CS~


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## BBQ (Nov 16, 2010)

meadow said:


> Isnt another purpose of a ground rod to bring the soil at the same or near same potential as the ground and neutral. ie, some one using a drill thats grounded outside will be of similar potential as everything else around him or am I missing something?


That is one of the things said in the NEC but it really is not possible to do so.

You would have to be practically standing on the rod itself to be protected.


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## BuzzKill (Oct 27, 2008)

like you said BBQ, 250.4(a)(5) says it all...leave all the discussion to the scientists and theorists; as a practical value as a ground fault current path, rods have none.


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## McClary’s Electrical (Feb 21, 2009)

Cletis said:


> how bout 120k
> 
> with 0.5 ohm grounding system
> 
> ...


 

Don't forget this post from another thread but it makes sense.




raider1 said:


> Contrary to popular belief the earth itself is considered to have a resistance of 0. This is due to the infinite number of parallel paths once current enters the earth. Kirkoff's Current Law states that the total resistance of resisters in parallel will always be less then the smallest resister in the circuit.
> 
> The 25 Ohms that you are using in your example represents the resistance of the connection between the grounding electrode and the earth itself.
> 
> Chris





raider1 said:


> Contrary to popular belief the earth itself is considered to have a resistance of 0. This is due to the infinite number of parallel paths once current enters the earth. Kirkoff's Current Law states that the total resistance of resisters in parallel will always be less then the smallest resister in the circuit.
> 
> The 25 Ohms that you are using in your example represents the resistance of the connection between the grounding electrode and the earth itself.
> 
> Chris


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## chicken steve (Mar 22, 2011)

It really begs some sort of _Low R Earth Society_ to go lobby the nec McClary.....~CS~


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## Cletis (Aug 20, 2010)

*computing*



chicken steve said:


> It really begs some sort of _Low R Earth Society_ to go lobby the nec McClary.....~CS~


Stay tuned everyone...I plugged in chicken steve's comment above. I've been waiting for the new Intel 1 teraflop chip to process it. I'll post when it spits out english translation....


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## Zog (Apr 15, 2009)

rexowner said:


> Ignoring the fact that your basic premise is incorrect, from what little
> information you give, your math seems to be wrong as well. If an
> 8 foot ground rod were 40 ohms, since resistance should be proportional
> to length,


Doubling the length reduces resistance by about 40%



rexowner said:


> a 10 foot of the same diameter would be 32 ohms. Since surface
> area is directly proportional to diameter (you must have used the square
> or something else wrong), going to 5/8 from 1/2 would
> bring this down to 25.6ohms.


No, per UL testing diamater has very little effect on resistance, just a percent or two for 2x larger diameter. 



rexowner said:


> Two in parallel - 12.8 ohms.


Not really, due to many paths through earth the rule of parallel resistances does not apply to ground rods, 2 rods will reduce by about 40%, 3 rods by about 60%. Spacing makes a big difference as well.


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## Zog (Apr 15, 2009)

BBQ said:


> That is one of the things said in the NEC but it really is not possible to do so.
> 
> You would have to be practically standing on the rod itself to be protected.


Well, equipotential grounding systems are used to elliminate step voltages in switchyards all the time, so it is very possible. But as far as LV systems and a single rod, not gonna happen.


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## captkirk (Nov 21, 2007)

Cletis said:


> I hear through the grapevine and Tom that driving 1 - 8ft 1/2 ground rod is basically useless. The national avg (avg may vary location, seasonal) is around 40 ohms.
> 
> And by a quick ohms law eq. that would be
> 
> ...


 you seem to be a bit smarter than your average *******..:whistling2:


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## RIVETER (Sep 26, 2009)

BBQ said:


> Average lightning bolt 5 miles long.
> 
> Makes it through 5 miles of high impedance air, I doubt a ground rod one way or the other is going to make much difference.


What if lightning strikes in a farmer's field and there is no ground rod driven...will it go elsewhere?


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## BuzzKill (Oct 27, 2008)

captkirk said:


> you seem to be a bit smarter than your average *******..:whistling2:


gimme a break, 
anybody can read from an Ugly's.


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## BuzzKill (Oct 27, 2008)

RIVETER said:


> What if lightning strikes in a farner's field and there is no ground rod driven...will it go elsewhere?


are you f*cking serious?


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## RIVETER (Sep 26, 2009)

BuzzKill said:


> are you f*cking serious?


Oh you of limited working speech. Why don't you just say " What do you mean by that"? Does cursing, at work always get the results that you want?


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## chicken steve (Mar 22, 2011)

Cletis said:


> Stay tuned everyone...I plugged in chicken steve's comment above. I've been waiting for the new Intel 1 teraflop chip to process it. I'll post when it spits out english translation....


The nec doesn't believe the earth is, or can be a conductor Cletis

thus i eqaute their stance with the Flat Earth Society

~CS~


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## BBQ (Nov 16, 2010)

chicken steve said:


> The nec doesn't believe the earth is, or can be a conductor Cletis
> 
> thus i eqaute their stance with the Flat Earth Society
> 
> ~CS~



As far as fault clearing below 600 volts the NEC is 100% correct in it's assessment of the earths ability to carry current.

But by all means continue with your unfounded rantings. :laughing:


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## chicken steve (Mar 22, 2011)

BBQ said:


> As far as fault clearing below 600 volts the NEC is 100% correct in it's assessment of the earths ability to carry current.
> 
> .


 
i look forward to your validation of this point BBQ

~CS~


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## don_resqcapt19 (Jul 18, 2010)

Zog said:


> Well, equipotential grounding systems are used to elliminate step voltages in switchyards all the time, so it is very possible. But as far as LV systems and a single rod, not gonna happen.


You could do the same thing for LV...but it is not practical. It would probably require a grid of 6" squares less than 6" below the surface to bring the step and touch potential down to a safe level for a typical 120/240 volt system. 

With a single grounding electrode, you have ~85% of the full voltage when you are 3' away from the rod.


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## rexowner (Apr 12, 2008)

Zog said:


> Doubling the length reduces resistance by about 40%
> ....
> No, per UL testing diamater has very little effect on resistance, just a percent or two for 2x larger diameter.
> 
> ...


Yes, I was basically (wrongly) assuming that rod/earth contact resistance
was the largest component. Not true.

Your message prompted me to read Fluke's paper here:
http://support.fluke.com/find-sales/Download/Asset/2633834_6115_ENG_A_W.PDF
which had a little bit more detailed info consistent with your numbers.
If I may oversimplify what Fluke had to say, the largest component of
resistance is the "layers" of earth surrounding the rod, and that doesn't change
that much with a larger diameter. Was definitely worthwhile reading.

I appreciate it when the site helps me better understand something I hadn't
been thinking about clearly, so thanks Zog and the OP Cletis.


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## BBQ (Nov 16, 2010)

chicken steve said:


> i look forward to your validation of this point BBQ
> 
> ~CS~


Ohms law all day long.


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## Amish Electrician (Jan 2, 2010)

I'm going to somewhat disagree with Zog's post. My source is the data published in the American Electricians' Handbook.

One graph relates the length of the rod to the resistance. It's a graph with a pretty good curve; somewhere between 8-ft and 10-ft you clarly reach the point of diminishing returns, where adding length inproves the ground very little.

The other graph is for the distance between electrodes. From this graph you can see that there is a great improvement between, say, 5-ft separation and 6-ft, but not much improvement between 6-ft. and 7-ft. Ironic, isn't it, that 'farther' is better- though only to a point.

Ohams law? Well, if anything the math simply shows that the ground rod has NO role in clearing faults. That is, it does NOT help 'power company electricity' get back to the power company. All the ground rod can do is help static electricity get back into the earth; lightning is just one form of static.


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## Zog (Apr 15, 2009)

Amish Electrician said:


> I'm going to somewhat disagree with Zog's post. My source is the data published in the American Electricians' Handbook.
> 
> One graph relates the length of the rod to the resistance. It's a graph with a pretty good curve; somewhere between 8-ft and 10-ft you clarly reach the point of diminishing returns, where adding length inproves the ground very little.
> 
> .


We are looking at the same graphs, I should have metioned the point about length not improving resistance much after 8 feet. Good point. :thumbup:


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## chicken steve (Mar 22, 2011)

BBQ said:


> Ohms law all day long.


okay, lets roll BBQ

we've a pad mount Xformer w/G-ring & rods

it's only 30 or so feet from the building meter

which has a few G-rods

so.....

_soil wet_

_soil dry_

_soil akaliline_

_soil acidic_

ohmic values please....

_~CS~_


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## Cletis (Aug 20, 2010)

*?*



chicken steve said:


> okay, lets roll BBQ
> 
> we've a pad mount Xformer w/G-ring & rods
> 
> ...


I'll guess 0.5-140 ohms ? with 40 being avg


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## BBQ (Nov 16, 2010)

chicken steve said:


> okay, lets roll BBQ
> 
> we've a pad mount Xformer w/G-ring & rods
> 
> ...



CS, dont act like idiot. 

Same place six months later is the soil still wet?

If we were counting on the earth as a fault path in that spot would it be reliable?


And if the NEC did say we could use the Earth as a fault path I am sure you would find fault with that as that ia all you ever do.


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## frenchelectrican (Mar 15, 2007)

chicken steve said:


> okay, lets roll BBQ
> 
> we've a pad mount Xformer w/G-ring & rods
> 
> ...


 
Chicken Steve.,

Normally I don't useally say something about this but right now all I did say :blink:

You will not able get a constant answer due there is a infenity answer to get the excat numbers so try do the test one day and then do it again couple months run the test again with same methold as you did the first and the result will NOT be the same at all.

I am pretty sure someone did ran the test and the answer will kinda suprise ya it will really varies alot.

Merci,
Marc


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## chicken steve (Mar 22, 2011)

Our old 250.32(b) was modified a few code cycles ago, adressing the issue of multiple returns FrenchElectrician, most of us aware of the issues of earthing multiple nuetrals in proximity agreed 

the simple fact is, the_ physics_ of electricity do _not _change at any given voltage

the conductivity of any given substance is relative to it's dielectric properties, lesser voltages _merely_ means less prevelant qualities

Gustav Kirchoff detailed this phenomenon on the shoulders of his elder countryman Georg Ohms findings

the examples of earth _conductivity_ @ higher voltages bear this out

http://en.wikipedia.org/wiki/Single-wire_earth_return

@ Wardenclyffe Tesla made the assertion the earth is a charged body floating in space
http://en.wikipedia.org/wiki/Wardenclyffe_Tower

JP Morgan shut down the project when he realized that metering it all would be difficult

~CS~


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## swimmer (Mar 19, 2011)

What is the instrument called that the inspector uses to check resistance from the ground rod to the earth?


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## Zog (Apr 15, 2009)

swimmer said:


> What is the instrument called that the inspector uses to check resistance from the ground rod to the earth?


3 point fall of potential ground resiistant test set. This one is my favorite model. http://www.groundtesterstore.com/p3500/aemc_3620_(150ft_kit).php


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