Water pipe & supplemental electrode

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Dennis Alwon

Dennis Alwon

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Water pipe is an electrode-- now it needs a supplemental electrode- my choice rods. Now the question is 1 or 2 ground rods? Assume 25 ohms is not reachable.
 
Dennis Alwon said:
That doesn't make sense-- 2 rods would not be 25 ohms around here so why would that be an electrode.
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Because the NEC states that 2 rods qualify as an electrode regardless of the ohm value they can achieve. One rod also qualifies as an electrode if you can get down to the magical 25 ohms.
 
It is pretty clear that if you use a ground rod as your supplemental electrode it still has to meet the 25 Ohm test or have two rods.

250.53 Grounding Electrode System Installation.
***
(D) Metal Underground Water Pipe. If used as a grounding
electrode, metal underground water pipe shall meet the
requirements of 250.53(D)(1) and (D)(2).
***
(2) Supplemental Electrode Required. A metal underground
water pipe shall be supplemented by an additional electrode of
a type specified in 250.52(A)(2) through (A)(8). If the supplemental
electrode is of the rod, pipe, or plate type, it shall
comply with 250.53(A).
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250.53 Grounding Electrode System Installation.
(A) Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate
electrodes shall meet the requirements of 250.53(A)(1)
through (A)(3).
(1) Below Permanent Moisture Level. If practicable, rod,
pipe, and plate electrodes shall be embedded below permanent
moisture level. Rod, pipe, and plate electrodes shall be free
from nonconductive coatings such as paint or enamel.
(2) Supplemental Electrode Required. A single rod, pipe, or
plate electrode shall be supplemented by an additional electrode
of a type specified in 250.52(A)(2) through (A)(8). The
supplemental electrode shall be permitted to be bonded to one
of the following:
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Note that the water pipe is 250.52(A)(1) so is specifically excluded from being a supplemental electrode.

note also that the code does not differentiate between a single rod that is also connected to a water pipe and one that is not connected to a water pipe. 250.53(A)(2) applies regardless.
 
Under the 2008 NEC, the code section is 250.56 regarding ground rod resistance and whether or not one or two are required, and also covers the 6-foot minimum distance if two rods are used.

If you have one rod at 20 ohms, that is sufficient. If you have two rods, it qualifies as the supplemental electrode and resistance is irrelevant by the letter of the code. Doesn't matter if its 3 ohms or 30 quadrillion ohms or somewhere in between.

Edited to add... What Rob wrote, plus code citation.
 
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I have always used 2 rods but then I read the NC interpretation and they are saying only one is required. I started this thread to make sure I had always interpreted it correctly. I still don't get the fact that a single rod isn't an electrode. It is an electrode just not a good one
 
Dennis Alwon said:
I have always used 2 rods but then I read the NC interpretation and they are saying only one is required. I started this thread to make sure I had always interpreted it correctly. I still don't get the fact that a single rod isn't an electrode. It is an electrode just not a good one
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Unless the single rod is supplemented by another electrode or it's 25 ohms or less it's not an electrode in the eyes of the NEC.
 
So where does it say a single rod is not an electrode. In 250.52 it states electrodes and a rod or pipe is an electrode... it does not say 2 must be used to be an electrode. I get that 250.53 states you need 2 but does that doesn't mean one is not an electrode....What am I missing.
 
Dennis Alwon said:
So where does it say a single rod is not an electrode. In 250.52 it states electrodes and a rod or pipe is an electrode... it does not say 2 must be used to be an electrode. I get that 250.53 states you need 2 but does that doesn't mean one is not an electrode....What am I missing.
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I agree with Rob, one rod is not an electrode on its own unless it meets the 25 or less requirement.

Petersonra has the correct article section.

Roger
 
I do agree with the need for 2 rods but somehow I was looking for the exact wording that said one rod is not an electrode. It states that but indirectly. We have always added 2 rods when a water pipe electrode was also existing because if the water pipe got changed to plastic then the two rods would be the main electrode.
 
My interpretation is that one rod is an electrode, regardless of its resistance value. What matters is that a single rod does not comprise a code-compliant grounding electrode system unless it is under 25 ohms or unless you install a second rod.
 
Dennis Alwon said:
That doesn't make sense-- 2 rods would not be 25 ohms around here so why would that be an electrode.
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Suppose one rod tests at 80 Ohms. Then you drive an identical rod at the requisite minimum 6 ft away. I cannot fathom how the combination of the two rods in parallel in this condition is anything less than 40 Ohms. Is there something going on in the physics of ground rods, that makes the conductance of two rods better than the sum of their individual conductances?

What am I missing, about how "two rods and done" excuses you from any ohm requirements? And why you don't need to continue driving rods until it is 25 Ohms or less.
 
Dennis Alwon said:
I do agree with the need for 2 rods but somehow I was looking for the exact wording that said one rod is not an electrode. It states that but indirectly. We have always added 2 rods when a water pipe electrode was also existing because if the water pipe got changed to plastic then the two rods would be the main electrode.
Click to expand...

I agree that the wording is somewhat poor because they're calling the single rod an electrode even though it may not meet all of the conditions of being an electrode. If I have two rods pounded only 7' into the ground that's not an electrode either.
 
infinity said:
I agree that the wording is somewhat poor because they're calling the single rod an electrode even though it may not meet all of the conditions of being an electrode. If I have two rods pounded only 7' into the ground that's not an electrode either.
Click to expand...

It is not a code legal GE.

It could be an auxiliary electrode though.
 
infinity said:
. . . they're calling the single rod an electrode even though it may not meet all of the conditions of being an electrode.
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But it does. The definition of "grounding electrode" in article 100 only requires it to be a conducting object that provides a direct connection to planet Earth.

As I said earlier, the question is not whether any particular conducting object can be called a "grounding electrode." The question is whether any such object can, by itself, comprise a complete and compliant grounding electrode system.
 
Carultch said:
And why you don't need to continue driving rods until it is 25 Ohms or less.
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Because the number 25 is essentially arbitrary, and because some locations can never achieve that number regardless of the number of rods installed. They had to draw a line somewhere, and "two and done" is where they drew that line.
 
charlie b said:
But it does. The definition of "grounding electrode" in article 100 only requires it to be a conducting object that provides a direct connection to planet Earth.

As I said earlier, the question is not whether any particular conducting object can be called a "grounding electrode." The question is whether any such object can, by itself, comprise a complete and compliant grounding electrode system.
Click to expand...

Which was my point and I believe that is what Dennis is trying to convey as well. The wording is poor, it should state that it only becomes an electrode when all of the installation conditions are met.
 
Carultch said:
Suppose one rod tests at 80 Ohms. Then you drive an identical rod at the requisite minimum 6 ft away. I cannot fathom how the combination of the two rods in parallel in this condition is anything less than 40 Ohms. Is there something going on in the physics of ground rods, that makes the conductance of two rods better than the sum of their individual conductances?

What am I missing, about how "two rods and done" excuses you from any ohm requirements? And why you don't need to continue driving rods until it is 25 Ohms or less.
Click to expand...

I have no idea of the physics of it, but the spacing between ground rods can affect the efficiency.

(3) Supplemental Electrode. If 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.


Informational Note: The paralleling efficiency of rods is
increased by spacing them twice the length of the longest rod.
 
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