Can a ground fault through dirt trip the OCPD?

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George Stolz

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Staff member
Location
Windsor, CO NEC: 2017
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I maintain this for a long time but the majority here is mislead by the general 'understanding' of grounding as it is propagated by the MHE.
I don't believe I have ever seen anyone say "Dirt is not conductive" and not be corrected.

When it comes to safety, I believe it's a good idea for people to crawl before they walk. That is, if we get it into someone's head the simple message, that the earth is a lousy conductive path for our purposes (i.e. for people that work with up to 480V) then after that has been established then there's no harm in exploring the specifics.

If someone were to come away from this discussion thinking they could omit the EGC of a circuit and drive a ground rod, that would be no good.
 

tryinghard

Senior Member
Location
California
?The earth shall not be considered as an effective ground-fault path?, 250.4(A)(5), if used as such will be in violation. This is just the fact, neither positive nor negative, for or against. :cool:
 

crossman gary

Senior Member
I sure hope I made that point like 15 times in the 2 threads on this subject.

Do the grounding and bonding according to the NEC!!!!!
 

crossman gary

Senior Member
It's like Laszlo said, and I will paraphrase, while the conductive charactaristics of the wiring and electrical components is known, the conductivity of the dirt is an unknown, and changes depending on conditions, therefore it would not be prudent to rely on it for the safety of people and property.
 

dereckbc

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Location
Plano, TX
Crossman Gary, I am intrigued with your experiments. You remind me of myself when I was a young ambitious engineer, especially when I worked for a POCO as a substation engineer with some cool toys at my disposal.

I am not one bit surprised by the un ordinary low impedance readings you are getting in Houston Black Gumbo soil. I have took part in design of two large telephone offices and one very large data center in the Houston Metro area and had similar results. On the first encounter I did not believe my contractors results and hired another one. All sites I have done in the area involved a ring and chemical rod combinations and we were getting well below 1 ohm. So low we could not really make a measurement.

It caused us some significant problems, mainly very large return currents on the GEC/GES connection which was solved with transformers.

It does sound like you are coming away with the right conclusions, you cannot rely on earth as a conductor for low voltage applications, or I should say NEC applications. However you found an excellent location for a future SWER power station.
 
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crossman gary

Senior Member
I am not one bit surprised by the un ordinary low impedance readings you are getting in Houston Black Gumbo soil. I have took part in design of two large telephone offices and one very large data center in the Houston Metro area and had similar results.
Sorry for the delayed response. Thank you for the data which backs up my findings.

On the first encounter I did not believe my contractors results and hired another one. All sites I have done in the area involved a ring and chemical rod combinations and we were getting well below 1 ohm. So low we could not really make a measurement.
I can easily believe that if my 4 foot deep pipes had good conductivity, then an enhanced electrode system would be very low resistance.

It caused us some significant problems, mainly very large return currents on the GEC/GES connection which was solved with transformers.
I never thought of that... with the electrode and dirt path in parallel with the neutral back to the utility xfmr, the impedance was so low that significant neutral current was flowing through the ground path? Makes sense. I need to put a clmp-on ammeter on my GEC to see if we have the same "problem".

It does sound like you are coming away with the right conclusions, you cannot rely on earth as a conductor for low voltage applications, or I should say NEC applications. However you found an excellent location for a future SWER power station.
I hope any misunderstandings have been cleared up. As mentioned, I never championed the idea of using earth as part of any feeder or branch circuit. I just wanted to show that the earth is sometimes a better conductor than is normally taught.

Again, thanks for the informative post.
 

gpedens

Member
can dirt trip an OCPD

can dirt trip an OCPD

yep in theory given a big enough volume even glass or any other insulator can trip an ocpd. its just a matter of area versus length. If you deal in AC dont forget capacitve and inductive coupling too. it works it just aint practical sometimes
 
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