Deep Ground Rods

[hurk27]

My only point is that there is no evidence that a 20-ohm grounding system is any safer than a 100-ohm or even higher system...

I would guess there are millions of structures with grounding systems well above the magical 25-ohm threshold that have never been exposed to a hazard that could have been reduced or eliminated with a lower resistance grounding system.

And at the same time, there are probably millions of Lightning Protection Systems and other grounding systems that are completely successful with relatively high grounding resistance...

My thoughts exactly, and the results of this thread:
http://forums.mikeholt.com/showthread.php/116358-Earth-Shells-Experiment-time-to-eat-crow!

I see requirements for ground rods all the time, and in most all cases are not based upon any kind of scientific evaluation, but are put in the requirements just because thats what been done for so many years, now this is not talking about true lightning protection systems, or ground planes for broadcast radio, or short wave antennas, which are of a whole different design and effect.

Some of the books I was studying from my Ramsay test had instructional chapters identifying the purpose of grounding electrodes as for the safety from shock hazards, and even had questions and answers to the same effect, it even in one place stated that it is for the operation of OCPD, and of course we know the difference (or should) there are many from all walks of life who don't, including engineers who put these requirements into their design thinking they have done something to make the world a safer place, when we know this is false.

I don't know how the change this kind of thinking, but I try when ever the opportunity come up.

 

[brian john]

My only point is that there is no evidence that a 20-ohm grounding system is any safer than a 100-ohm or even higher system...

...

And as much as the electrode system is stressed over by engineers, electricians and inspectors IMO, it is one of the least important items in the overall grounding system.

The major grounding issues are often overlooked.

 

[saadt]

Ground rod 3/4" x 10 ft at 40 ft

Ground rod 3/4" x 10 ft at 40 ft

Hello Every one....

Can we install a 3/4" X 10ft ground rod at 40ft deep? I read this requirement and I'm not sure if it's possible.

Also, I read in the specification if we did not get the required resistance, that we should install 30ft long ground rod, do they make ground rods that long, or you think they meant the depth?

Thanks you........

A 3/4" X 10 ft ground rod at 40 ft deep has a resistance of 28,59 Ohms in a homogeneous soil of 100 Ohms. m resistivity. This same rod at 2 ft deep has a resistance of 30,39 Ohms in the same soil.

 

[saadt]

Hello Every one....

Can we install a 3/4" X 10ft ground rod at 40ft deep? I read this requirement and I'm not sure if it's possible.

Also, I read in the specification if we did not get the required resistance, that we should install 30ft long ground rod, do they make ground rods that long, or you think they meant the depth?

Thanks you........

A 3/4" X 10 ft ground rod at 40 ft deep has a resistance of 28,59 Ohms in a homogeneous soil of 100 Ohms. m resistivity. This same rod at 2 ft deep has a resistance of 30,39 Ohms in the same soil.

 

[don_resqcapt19]

A 3/4" X 10 ft ground rod at 40 ft deep has a resistance of 28,59 Ohms in a homogeneous soil of 100 Ohms. m resistivity. This same rod at 2 ft deep has a resistance of 30,39 Ohms in the same soil.

It seems unlikely that the soil would be homogeneous between 2' and 40'. I believe the only reason that you would use deep driven rods would be to get into soil with a lower resistivity than what you would be in with a standard 8' or 10' rod.

 

[saadt]

3/4" X 10 ft ground rod at 40 ft deep

3/4" X 10 ft ground rod at 40 ft deep

The figures a gave for the different depths serve only to show that you gain a little for a much expensive alternative of 40 ft deep. Notwithstanding, you are right when you say that in practice there no such thing as a homogeneous soil.

 

[defears]

I can see elaborate grounding systems for a high voltage service, like 13Kv. At least the earth assists with clearing faults at high voltages. But when the copper wire, rods, and time costs the same as the whole 208/120 volt 400 amp service, on a 10,000 sqft retail space, I think the engineer is not paying attention the actual job at hand.

 

[K8MHZ]

I can see elaborate grounding systems for a high voltage service, like 13Kv. At least the earth assists with clearing faults at high voltages. But when the copper wire, rods, and time costs the same as the whole 208/120 volt 400 amp service, on a 10,000 sqft retail space, I think the engineer is not paying attention the actual job at hand.

Actually, the most elaborate grounding systems are found in communications, not medium or high voltage transmission.

Check out the grounding of a cell phone tower or even a POTS MESA box. They are rather complicated and designed to not only take hits, but to minimize the inductive effects of the hit to the equipment on the site.

A pole with 138kV will have one ground rod and a #6 wire connected to it. I have pics to prove that, by the way.

 

[K8MHZ]

At least the earth assists with clearing faults at high voltages.

Really?

That's gotta be hard on the cattle.

 

[defears]

K8MHZ,
So then explain how SWER systems work.
And yes, it would be hard on the cattle.:roll:

I was just saying it would be more usefull on a higher voltage system, than any low voltage system.

 

[arknack]

Deep Ground Rods

Interesting thread. I work for a Gas and Electric utility company and our standard on the electric side is 40 feet. I am now on the gas side and we drive the rods as deep as they will go. Our goal is not 25 ohms but 5 ohms. The reason is noise and lighting damage to our computer equipment out in the field. When I first moved into this department my task was to stop our lighting damage. One sight was really bad. It would fail in every storm. At that location I drove 128 foot rod into the ground. Notice I did not say deep because I am sure it veered but it was long. After that fix I am still waiting (17 years) for that unit to fail.

As for cost, driving ground rod is cheap. My cost is getting the crew out there and set up. The rods we use have a slip coupling that cold welds itself together as it is being driven. We use a similar process that the U-tube video showed except it is a jack hammer with a boom truck.

ps: At new station we now put in ground grids