25 ohms

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quandaklin

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The great state of Texas
I am in disagreement with several coworkers concerning NEC requirements for ground rods. I say if you have 1 rod with a resistance of more than 25 ohms then you add 1 more rod and that is it. No mater what the resistance is you are in compliance with the NEC. They say you keep adding electrodes untill you get below 25 ohms no mater how many it takes. 10, 15 or what ever it takes to get below 25 ohms.
 
You are correct and win the bet if you had one.

250.56 Resistance of Rod, Pipe, and Plate Electrodes.
A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.
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Roger
 
Taking my inspector hat off, I say.

Install one ground rod and if it has a resistance of 400-ohm, who cares, walk away satisfied.

Putting my inspetor hat back on, I say.

Drive the two ground rods and don't worry about it. Don't worry about 25-ohms. It means nothing.
 
Inspectorcliff said:
Would that be the same as infinitely means something? Or what would that mean?:mad:
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Just a heads up bphgravity has taken a lot of time researching lightning protection, grounding, and the 25 ohm requirement. :smile:
 
I am going to take a wild guess that you are in Iraq and there is a bunch of idiots screaming about 25 ohms. Could I be correct?
 
jes25 said:
I am going to take a wild guess that you are in Iraq and there is a bunch of idiots screaming about 25 ohms. Could I be correct?
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He says he's in Texas.

Roger
 
A large majority of workers there are recruited from TX. And his situation is one I went through, in Iraq.
 
jes25 said:
A large majority of workers there are recruited from TX. And his situation is one I went through, in Iraq.
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But, I know where he posted from by his IP. :wink:

Roger
 
So I am wrong then. I guess Iraq is not the not the only place with misinformed workers.

I've only been back a couple months, so I got Iraq on the brain.
 
I remember reading that in a fault condition, 25% of the fault current typicaly travels down through the electrode, while the remainder of the current, 75%, goes up the system neutral back to the transformer and its system grounding methods, ie: butt rap,etc. I've also read that a typical 8ft rod, in best conditions, barely falls in the 25ohm range.

IF this information is correct, I think the electrode system is very important, BUT I've NEVER had a inspector question a electrodes resistance.

I also think that using the reinforcement steel and a footer ground is much, much lower resistance to ground than a rod....but who wants to bust a footing with a lighting bolt?
 
I just got a legit offer to go to Iraq for a one year tour as an electrical consultant but the money just wasnt enough to leave the family for a year. If it would pay off the mortgage I would reconsider.
 
quogueelectric said:
I just got a legit offer to go to Iraq for a one year tour as an electrical consultant but the money just wasnt enough to leave the family for a year. If it would pay off the mortgage I would reconsider.
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To each their own, but you couldnt pay me enough....I'd flip humburgers, mop floors, pick up pop bottles, and eat P&J sandwiches...first
 
Mule said:
To each their own, but you couldn't pay me enough....I'd flip hamburgers, mop floors, pick up pop bottles, and eat P&J sandwiches...first
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They could make me an offer that would pay off my mortgage, but then I just found out this evening that I have 12 months left on my mortgage.
 
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