HOW FREQUENTLY GROUNDING RESISTANCE NEEDS TO BE INSPECTED ??

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ActionDave said:
What does that have to do with low voltage systems?
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Please reread post #37. What did post #37 have to do with low voltage systems? My post #39 was meant only as an added informational note for substations. Though in the broader context I suggested to pay attention to touch as well as step potentials.

In low voltage systems do you think touch and step potentials could be an issue? Example, the differences where the earth grounding electrode system resistance is 25 ohms compared to 5 ohms?

Just curious what does your statement in post #34 have to do with low voltage systems for the purposes of the OPs original posted message?
Somewhere there is a scientist working at the South Pole with some sensitive electronic equipment. How deep is his ground rod?

What about the Navy submarines? How do they manage?
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You forgot airplanes.....

If you want answers to these questions you should start your own thread. I would then be glad to post an answer.



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Jamesco said:
In low voltage systems do you think touch and step potentials could be an issue? Example, the differences where the earth grounding electrode system resistance is 25 ohms compared to 5 ohms?

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Low system earth resistance will not help with step and touch potentials. You cant "out earth" your way out of step and touch potentials. The only way to do that is with a equipotential grid.
 
ActionDave said:
I think the difference between 25 ohms and 5 ohms is of no value at all in a low voltage system.
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I think the key thing to realize is you can't bond the earth. I don't think we would gain anything even with, say, a super low .25 ohm resistance. You only can "bond " the dirt within a few feet of the electrode. Go to great lengths to get a low resistance, and unfortunately you have to do it all over again once you move a few feet away.
 
electrofelon said:
I think the key thing to realize is you can't bond the earth. I don't think we would gain anything even with, say, a super low .25 ohm resistance. You only can "bond " the dirt within a few feet of the electrode. Go to great lengths to get a low resistance, and unfortunately you have to do it all over again once you move a few feet away.
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I think of Dirt Worshipers like the aliens it Toy Story,
The-claw.jpg

only they all chant "The Ground" instead of "The Claw".
 
Ohms Law.

Please take the time and watch the entire video.
https://www.youtube.com/watch?v=Yg6G5VUSsWA

For Power Quality of sensitive equipment in a facility which would do a better job, during a lightning storm, to limit excessive voltage caused by lightning from entering the facility an causing damage and or system failure to sensitive equipment? An electrode ground resistance of 50 ohms or an electrode ground resistance of 3 ohms? Use Ohms Law.


Please post your thoughts.


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For most installations, it just does not make any real difference what the resistance to ground is as long as there is some connection.

For a very few situations it is important. I am not sure it is as important as they make it out to be though. I suspect that like many people they are afraid to change their standards becasue what they have works and if they change it and something bad happens the change will be blamed.
 
petersonra said:
For most installations, it just does not make any real difference what the resistance to ground is as long as there is some connection.
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Agree.
For a very few situations it is important. I am not sure it is as important as they make it out to be though. I suspect that like many people they are afraid to change their standards becasue what they have works and if they change it and something bad happens the change will be blamed.
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I know for sure that's true. I've done a lot of work on cell sites. Talking with the techs about what works and what doesn't after the site has been up for a while was quite interesting.
 
GoldDigger said:
As an illustration of how ground electrode impedance can vary with rod length, Mike H. worked his way up one 10' segment at a time to 50' ground rods in his Florida soil in a nice video on measuring ground electrode impedance.
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I remember watching that some while ago. As I recall, he still couldn't get the resistance below 25 ohms even with 50 feet of rod.
 
gadfly56 said:
I remember watching that some while ago. As I recall, he still couldn't get the resistance below 25 ohms even with 50 feet of rod.
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Actually I just looked again. At 40 feet of rod he had the resistance down to 22.5 ohms and the current at 5.6 amps. In the end, he had two ground rods, each at 50 feet for a total resistance of 10.8 ohms and a current of 13.24 amps. Not enough to trip the breaker.

My area is near the glacier terminal moraine. You'd be lucky to get down 10 feet. Fifty feet would be a pipe dream.
 
redundant

redundant

gadfly56 said:
Actually I just looked again. At 40 feet of rod he had the resistance down to 22.5 ohms and the current at 5.6 amps. In the end, he had two ground rods, each at 50 feet for a total resistance of 10.8 ohms and a current of 13.24 amps. Not enough to trip the breaker.
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I have a question about this thread.

The electrical system in a structure is bonded to the grounded conductor at the service? The grounded conductor returns to the power plant and along the way it is connected to earth at multiple points? I believe there is a ground rod next to the pole near my house and many other poles along the way to the power plant?

At the house or structure the GES is connected to the earth via a #6 copper conductor. It would appear the grounded conductor would be a much better return to earth than the small conductor that connects to the ground rod at the structure? Therefore, what is the benefit of the GES?
 
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Greg1707 said:
I have a question about this thread.

The electrical system in a structure is bonded to the grounded conductor at the service? The grounded conductor returns to the power plant and along the way it is connected to earth at multiple points? I believe there is a ground rod next to the pole near my house and many other poles along the way to the power plant?

At the house or structure the GES is connected to the earth via a #6 copper conductor. It would appear the grounded conductor would be a much better return to earth than the small conductor that connects to the ground rod at the structure? Therefore, what is the benefit of the GES?
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You are absolutely correct in that the network of electrodes all over the place is a lesser resistance then what you will typically get out of a driven rod or two at just one location. And that is good enough for most applications. Some sensitive equipment applications it may be more important to have a low resistance electrode at the building/structure served.
 
gadfly56 said:
Actually I just looked again. At 40 feet of rod he had the resistance down to 22.5 ohms and the current at 5.6 amps. In the end, he had two ground rods, each at 50 feet for a total resistance of 10.8 ohms and a current of 13.24 amps. Not enough to trip the breaker.
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In the end, he had two ground rods, each at 50 feet for a total resistance of 10.8 ohms and a current of 13.24 amps. Not enough to trip the breaker.
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That's not the purpose of the system ground. That's what the equipment ground is for.
 
Greg1707 said:
I have a question about this thread.

The electrical system in a structure is bonded to the grounded conductor at the service? The grounded conductor returns to the power plant and along the way it is connected to earth at multiple points? I believe there is a ground rod next to the pole near my house and many other poles along the way to the power plant?

At the house or structure the GES is connected to the earth via a #6 copper conductor. It would appear the grounded conductor would be a much better return to earth than the small conductor that connects to the ground rod at the structure? Therefore, what is the benefit of the GES?
Click to expand...

The purpose of the system ground is, "to limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines and that will stabilize the voltage to earth during normal operation."
NEC 250.4(A)(1) Electrical System Grounding.
 
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