8' ground rod

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electrofelon said:
Unfortunately the only way this would work is to have an elaborate conductive grid or mat. A bunch of rods is not going to do anything no matter how long they are. That is not their purpose.
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You're right about that. Two ground rods is essentially worthless but it's the principle that matters.

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I dare you to try this experiment:

Run a 300 ft long feeder out to a detached garage, which is about 500 ft away from the transformer at the pole (which has it's neutral grounded). Now disconnect all your grounding electrodes from your system.

Now that those useless buggers are gone, wet your hands and feet and touch the neutral bus if your sub panel.

Just make sure you have a buddy with a defibrillator nearby.

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DrSparks said:
I dare you to try this experiment:

Run a 300 ft long feeder out to a detached garage, which is about 500 ft away from the transformer at the pole (which has it's neutral grounded). Now disconnect all your grounding electrodes from your system.

Now that those useless buggers are gone, wet your hands and feet and touch the neutral bus if your sub panel.

Just make sure you have a buddy with a defibrillator nearby.

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The electrodes will not make any difference, the earth has too high a resistance. The grounding electrodes will not "pull" the potential from neutral to earth any closer.
 
electrofelon said:
The electrodes will not make any difference, the earth has too high a resistance. The grounding electrodes will not "pull" the potential from neutral to earth any closer.
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What does that matter? Think of what the resistance of your body through your feet on a concrete slab, through the earth and back to the transformer is... it's quite evidently low enough to cause death. Would you say a copper rod driven 8 ft into the earth would have less resistance than a human body standing on concrete?

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DrSparks said:
What does that matter? Think of what the resistance of your body through your feet on a concrete slab, through the earth and back to the transformer is... it's quite evidently low enough to cause death. Would you say a copper rod driven 8 ft into the earth would have less resistance than a human body standing on concrete?

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The contact resistance of the ground rod to earth is too great to make any difference. Ground rods do nothing to make an electrical system safe.
 
DrSparks said:
What does that matter? Think of what the resistance of your body through your feet on a concrete slab, through the earth and back to the transformer is... it's quite evidently low enough to cause death. Would you say a copper rod driven 8 ft into the earth would have less resistance than a human body standing on concrete?

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I dont understand what you are saying or proposing.
 
electrofelon said:
Because I am wearing rubber shoes, and even if I wasnt, the difference in potential between that conductor and whatever I am standing on wouldnt be more than a few volts.
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So you're saying the earthing of the neutral bus has absolutely nothing to do with that potential difference?

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DrSparks said:
Run a 300 ft long feeder out to a detached garage, which is about 500 ft away from the transformer at the pole (which has it's neutral grounded). Now disconnect all your grounding electrodes from your system.

Now that those useless buggers are gone, wet your hands and feet and touch the neutral bus if your sub panel.
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Nobody here would expect a neutral in a sub-panel to be at zero volts to earth.

A rod does not "force" the nearby earth to be at the same potential as the bus to which it's connected.

Do a bit of research on step potential.
 
LarryFine said:
Nobody here would expect a neutral in a sub-panel to be at zero volts to earth.

A rod does not "force" the nearby earth to be at the same potential as the bus to which it's connected.

Do a bit of research on step potential.
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instrumentationtools.com

Methods to Reduce Step Potential and Touch Potential in Substation

Step Potential and Touch Potentials are very important in substations because during ground faults all the ground current returns to
instrumentationtools.com instrumentationtools.com

Methods to Limit Step Potential and Touch Potential:
Step potentials and touch potentials can be reduced by employing one of the following methods:

By proving low resistance path to ground

By providing insulation layer between operating personnel and earth

By proper placing of ground conductors



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Multi-grounded neutral helps to reduce the dangerous step potential and touch potential during line-to-ground faults. By creating low impedance path back to the source, faults are quickly cleared by fault interrupters. Multiple grounding electrodes tied together helps to reduce the touch potentials at the fault point. With multiple neutrals, step potentials are usually not dangerous since fault currents spreads between several grounding electrodes



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DrSparks said:
Multi-grounded neutral helps to reduce the dangerous step potential and touch potential during line-to-ground faults. By creating low impedance path back to the source, faults are quickly cleared by fault interrupters. Multiple grounding electrodes tied together helps to reduce the touch potentials at the fault point. With multiple neutrals, step potentials are usually not dangerous since fault currents spreads between several grounding electrodes



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Except the code only allows you to ground the neutral at one point. Any grounding electrodes at separate structures regardless of how remote are not allowed to be tied to neutral. They are tied to the equipment grounding conductor bus.
 
One other statement I've seen as to reasoning for 8 ft of ground rod drivin as near to vertical as possible was to get the rod into more perminantly damp soil, as wet soil has lower resistance than dry soil.
Also, it used to be 10 ft rods, but I guess it was determined that the potential improvement in resistance was negligible between the 8 ft and 10 ft rods?
 
Buck Parrish said:
I know an electrician in Durham, The city inspector (Rowland) called him up and asked. Did you cut that ground rod off ? He said no way. The inspector says. Well I was wondering because their is half of one here leaned up against the house.
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Hahaha that's classic!

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Fred B said:
One other statement I've seen as to reasoning for 8 ft of ground rod drivin as near to vertical as possible was to get the rod into more perminantly damp soil, as wet soil has lower resistance than dry soil.
Also, it used to be 10 ft rods, but I guess it was determined that the potential improvement in resistance was negligible between the 8 ft and 10 ft rods?
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When was it that 10' rods were required?
 
infinity said:
When was it that 10' rods were required?
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Don't know if it was code, I was just starting in the field and just a grunt back in the early 80's and my boss told to us to drive in these 10 ft rods. Also used 10ft X 3/4in galvanized pipe. End would get smashed pretty good and have to cut off the smashed end with a hacksaw before clamping cable on.
 
DrSparks said:
So you're saying the earthing of the neutral bus has absolutely nothing to do with that potential difference?

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Correct. Take a look at this link and the graphic in post #6:

Step potential????

First off give me a laymens definition of Step Potential. When grounding inplant industrial substations,when does step potential come in to play and how do you combat it? ie: How do you calculate the fault current and how do you design a safe system???? dick
forums.mikeholt.com

Dirt is such a poor conductor that that it forms a steep voltage gradient when voltage imposed on it. If you try to "bond dirt" you will literally only bond a very small area like a square foot or less and then you are back to square one again. In high risk areas like substations, you essentially need a continuous conductor everywhere which is why they often employ these grids or mats so you are essentially always standing on a bonding conductor.
 
Fred B said:
Don't know if it was code, I was just starting in the field and just a grunt back in the early 80's and my boss told to us to drive in these 10 ft rods. Also used 10ft X 3/4in galvanized pipe. End would get smashed pretty good and have to cut off the smashed end with a hacksaw before clamping cable on.
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Sounds like one of those we always did it that way. I took a peek at the 1965 NEC and that still only required an 8' rod or pipe electrode.
 
Greentagger said:
For starters, where does one find a 4’ ground rod? Come on people, seriously.
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Telephone companies used to use them around here. Only 3/8" diameter as well

I have one that I welded a T handle to one end and use as a probe when excavating to help find other buried utilities and such.
 
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