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2 ground rods

ICE

ICE

Oh Well
Joined
Jun 23, 2011
Messages
12,918
Location
California
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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How does your jurisdiction treat that code section? Do they require a second rod whenever a single rod is required?

When I write the correction, I always spell out the word "feet" as in "a minimum 6 feet away from the first rod"

I still get these:

 
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For service changes and upgrades or new installations that don't have rebar in the footer, we always see 2 ground rods because of the same reasons stated above. 1) Not many have the equipment necessary to test and 2) Those that do have a hard time getting 25 ohms or less with our soils.

Here is a short story that I will make long.

I was always under the impression that if you had a water pipe that qualified as a grounding electrode, then if you added a rod outside, that was the 2nd electrode IF you could not prove the 25 ohm rule. In my little head, we had 2 grounding electrodes and since the water pipe was larger and longer and tied into a system underground, it was the main grounding electrode and the single rod added as the supplemental for the 25 ohm rule. I was corrected in person by Michael Johnston who sits on a few CMPs.

Of course, me being me, I had to question him and I asked: "So let me get this straight. If I have a house that has a plastic water main coming in and plastic pipe through out, I have to have 2 ground rods and agree. But, you are telling me that if I have a metallic water pipe that is considered a grounding electrode, I have to add 2 rods (if I don't meter the one) in addition to the water pipe?". His answer was "Yes, that is the intent."

I love to learn right from the source when possible. It make the humbling experience more bearable.
 
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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How does one know that the electrode does not have less than 25 ohms resistance to ground? The only way to know is an expensive three point test performed by a recognized agency.

Requiring a second rod is a knee-jerk reaction to a code section. A ground rod of unknown resistance to ground gets augmented with another rod because there is that possibility that there is more than 25 ohms resistance to ground. The possibility of a code violation results in not a little bit of effort and expense.

This sounds a lot like a jumper between the hot and cold pipes at the water heater.

Well in principle only because we're talking about a little bit of work and not much expense with the jumper.
 
ICE said:
How does your jurisdiction treat that code section? Do they require a second rod whenever a single rod is required?
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Each and every time. At a temp pole, remote building, service, or any place that a rod, pipe, or plate electrode is installed except as outlined in 250.54. The 2011 cycle cleared this up quite a bit by requiring two rods plain and simple (250.53(A)(2).
ICE said:
This sounds a lot like a jumper between the hot and cold pipes at the water heater.
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Bonding of metal water pipes comes from a different part of Article 250 than the installation of electrodes. The bonding of cold to hot metal water pipes is not found in the NEC.
 
Even if those rods were 6' apart the installation is not compliant. The way it is can cause a choke on the grounding electrode conductor. The metal cable must be bonded to the clamp
 
Dennis said:
Even if those rods were 6' apart the installation is not compliant. The way it is can cause a choke on the grounding electrode conductor. The metal cable must be bonded to the clamp
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You should have seen the rest of the work.
 
It doesn't take much to get a license in California. Most of what I see is some guy passing himself off as a licensed electrician. A lot of it is a general contractor that hires anybody that doesn't have burnt fingers to do electrical work.

This was presented as a water pipe bond. They were serious.



This had a general contractor behind it.



I had nothing to do with this job until they requested a final inspection. The job card had approvals through lath. All that was left was a final.
 
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ICE said:
A lot of it is a general contractor that hires anybody that doesn't have burnt fingers to do electrical work.
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Any electrician worth his salt I know wears readin glasses, has weathered wrinkled skin, grey hair and whiskers and burnt fingers.

And the best tree killer I know is missing a finger.
 
Here in Pueblo Colorado we have very dry soil with poor conductivity. By default the inspectors out here require two 8' rods driven a minimum of 6' apart.
 
RJJ said:
Dennis: Not sure I understand the comment on choke hold above? please explain?
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RJJ,

The metal sheath of the cable armor protecting the grounding electrode conductor must be bonded to the GEC at both ends. (See 250.64(E))

If you do not bond the cable armor and the grounding electrode conductor at both ends effectively making them a parallel path then during a lightning event any current flowing through the GEC would induce counter EMF in the cable armor. The resulting magnetic field will in essence "Choke" the grounding electrode conductor and resist the flow of current through the GEC to the earth. It has been estimated that not bonding both ends of a raceway or cable armor that contain a GEC could result in a 90% choke. The lightning induced currents would then try to find another path to the earth and may damage the electrical system or building.

This only affects ferrous cable armor and raceways, aluminum, stainless steel, red brass and PVC raceways and cable armor need not be bonded.

Chris
 
raider1 said:
RJJ,The metal sheath of the cable armor protecting the grounding electrode conductor must be bonded to the GEC at both ends. (See 250.64(E))

If you do not bond the cable armor and the grounding electrode conductor at both ends effectively making them a parallel path then during a lightning event any current flowing through the GEC would induce counter EMF in the cable armor. The resulting magnetic field will in essence "Choke" the grounding electrode conductor and resist the flow of current through the GEC to the earth. It has been estimated that not bonding both ends of a raceway or cable armor that contain a GEC could result in a 90% choke. The lightning induced currents would then try to find another path to the earth and may damage the electrical system or building.

This only affects ferrous cable armor and raceways, aluminum, stainless steel, red brass and PVC raceways and cable armor need not be bonded.

Chris
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thanks chris- that's a better explanation then I could have done...
 
"I was corrected in person by Michael Johnston who sits on a few CMPs."

We have a signed copy of his book here in the office....his father still lives in town...Nice man....
 
ICE said:
How does one know that the electrode does not have less than 25 ohms resistance to ground? The only way to know is an expensive three point test performed by a recognized agency. Requiring a second rod is a knee-jerk reaction to a code section. A ground rod of unknown resistance to ground gets augmented with another rod because there is that possibility that there is more than 25 ohms resistance to ground. The possibility of a code violation results in not a little bit of effort and expense.

This sounds a lot like a jumper between the hot and cold pipes at the water heater.

Well in principle only because we're talking about a little bit of work and not much expense with the jumper.
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Does your jurisdiction require a 3rd party test?

I allow the electrical contractor to perform the test if they have the proper equipment.

Chris
 
raider1 said:
Does your jurisdiction require a 3rd party test?I allow the electrical contractor to perform the test if they have the proper equipment.

Chris
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It has to be done by an approved agency.
 
ICE said:
It has to be done by an approved agency.
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Wow, is that a State rule or a local rule?

I can understand requiring an approved agency to perform the required performance test of a GFPE equipment in 230.95© but a simple ground resistance test to comply with 250.53(A)(2) Exception should be able to be done by an electrical contractor with the proper meter.

Chris
 
IMO, it is not worth the time or money to drive one rod and try and prove 25ohms. In fact around here it just won't happen and even if it were possible I would waste more time proving it then the job would be worth. If you don't use the concrete encased electrode then we just drive 2 rods and be done with it. Can't imagine getting an outside agency to do that
 
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