Supplemental Ground rod

[opes at askronald]

How does NEC 250.53(E) and NEC 250.66(A) apply? Very confusing but the way I interpret this to mean is that with a ground rod at my service, the connection between the service neutral and the ground rod(s) do not need to be larger than a no 6AWG copper when there are no additional grounding connections. Every AHJ I know requires that we size the GEC per table 250.66. Even though I do it some how this does not make sense as the ground rods for the most part maintain equal potential between the building and earth. I question how this larger conductor to earth would create a low impedance ground path without knowing dielectric of the soil. There is a method of checking the dielectric of the soil but would take probably miles between test probes to get an accurate reading. I have been there and done that and there is no practical way to measure the resistance of our earth. How does the larger conductor per NEC table 250.66 help? I can see NEC table 250.66 applying to bonding building steel to the service. Who can clarify this for me? Thanks in advance

 

[ActionDave]

I don't know what's confusing. 250.66 says "shall not be less than given in
Table 250.66, except as permitted in 250.66(A) through (C). Can't be written any clearer than that.

250.66(A) is titled Connection to a Rod and the words "shall not be required to be larger than 6 AWG copper" are as clear as can be written as well.

 

[jaggedben]

The connection to a single rod does not need to be larger than #6. If you have two rods connected to each other, and you run a single GEC to them from the service, then that GEC must be sized to 250.66.

 

[tom baker]

We tend to focus too much on Table 250.66, and not Section 250.66. Section 250.66 has parts A, B, C, which tells us the sizes to three type of electrodes, and then of course Table 250.66
The larger conductor in T 250.66 makes not difference as the impedance of a ground rod is typically quite high.
I have a slide chart from PolyPhaser Corp "lightning ground conductor voltage drop calculator"
10 ft of 6 AWG is instantaneous volt drop is 90 KV
10 ft of 0 is instantaneous volt drop 80 KV, so even a large wire does not drop the volt drop

 

[ActionDave]

The connection to a single rod does not need to be larger than #6. If you have two rods connected to each other, and you run a single GEC to them from the service, then that GEC must be sized to 250.66.

And 250.66 (A) says that grounding electrode conductor going to ground rods doesn't need to be any larger than 6AWG copper.

 

[tom baker]

The connection to a single rod does not need to be larger than #6. If you have two rods connected to each other, and you run a single GEC to them from the service, then that GEC must be sized to 250.66.

Sorry, no the wire between the rods is not a GEC and its bonding jumper, 253.53 5 C, and D 2

 

[wwhitney]

Sorry, no the wire between the rods is not a GEC and its bonding jumper, 253.53 5 C, and D 2

With a continuous conductor connected service -- rod 1 -- rod 2, you could certainly call that a GEC to rod 2. Regardless the sizing is the same when the only electrodes connected are ground rods.

Cheers, Wayne

 

[LarryFine]

The connection to a single rod does not need to be larger than #6. If you have two rods connected to each other, and you run a single GEC to them from the service, then that GEC must be sized to 250.66.

It (#6) applies to all rods, not just the last one.

 

[infinity]

How does NEC 250.53(E) and NEC 250.66(A) apply? Very confusing but the way I interpret this to mean is that with a ground rod at my service, the connection between the service neutral and the ground rod(s) do not need to be larger than a no 6AWG copper when there are no additional grounding connections. Every AHJ I know requires that we size the GEC per table 250.66.

Then you know quite a few AHJ's who don't know the NEC. As stated in this thread a #6 is all that's required to a ground rod, 200 amp service or 4000 amp service. Could be a single #6 GEC to the first rod, through the clamp unbroken and then on to the second rod or the GEC could end at the first rod and a bonding jumper would connect to the second rod.

 

[tom baker]

Then you know quite a few AHJ's who don't know the NEC. As stated in this thread a #6 is all that's required to a ground rod, 200 amp service or 4000 amp service. Could be a single #6 GEC to the first rod, through the clamp unbroken and then on to the second rod or the GEC could end at the first rod and a bonding jumper would connect to the second rod.

Good point.
Some AHJs want one wire and two clamps
But two wires and three clamps are ok and Art 250 now makes that clear.

 

[GoldDigger]

Then you know quite a few AHJ's who don't know the NEC. As stated in this thread a #6 is all that's required to a ground rod, 200 amp service or 4000 amp service. Could be a single #6 GEC to the first rod, through the clamp unbroken and then on to the second rod or the GEC could end at the first rod and a bonding jumper would connect to the second rod.

And that bonding jumper may well have to be larger than the GEC itself.
But you still save on wire overall.
If you run separate GECs to each rod you may be able to avoid that? Or would one of them still be considered a bonding jumper.

 

[wwhitney]

And that bonding jumper may well have to be larger than the GEC itself.

A bonding jumper run between ground rods is sized the same as a GEC run to a single ground rod. They are both sized per 250.66 (in particular, subsection (A)), as 250.53(C) indicates in the case of the bonding jumper.

Cheers, Wayne

 

[hillbilly1]

Then you know quite a few AHJ's who don't know the NEC. As stated in this thread a #6 is all that's required to a ground rod, 200 amp service or 4000 amp service. Could be a single #6 GEC to the first rod, through the clamp unbroken and then on to the second rod or the GEC could end at the first rod and a bonding jumper would connect to the second rod.

Exactly, I had a large 480 volt service where the inspector wanted to turn me down on the ground rod, I had a #4 bare copper to it, which was larger than it needed to be, which I told him. He said “Show me where it’s legal” pulled out the code book, and shown him. He said “I learned something today” and passed my installation! Been on many a job where the EE called for a 3/0 to a ground rod.

 

[jaggedben]

And 250.66 (A) says that grounding electrode conductor going to ground rods doesn't need to be any larger than 6AWG copper.

It (#6) applies to all rods, not just the last one.

I see now that this was changed in the 2017 NEC and I never caught up. What I said would be true under the 2014 NEC. Sorry for out of date info. That could be our OPs inspectors' problem, too.

 

[jaggedben]

Sorry, no the wire between the rods is not a GEC and its bonding jumper, 253.53 5 C, and D 2

I didn't say anything about the wire between the rods.

 

[opes at askronald]

Guys thanks for the many replies that confirm my understanding. I live in Florida what can I say. I used to do designs for healthcare projects and the subject of supplemental ground rods and the GEC came up. We all agreed in the office that the GEC between the service neutral bus and supplemental ground rods do not have to be larger than what is noted in NEC 250.66(A). We used NEC table 250.66 to bond the building steel to the service which frankly makes more sense. But in every instance the AHJ makes us size the GEC based on NEC table 250.66. I guess what I need to do is get an official ruling from NFPA and settle it once and for all. Thanks again

 

[electrofelon]

Guys thanks for the many replies that confirm my understanding. I live in Florida what can I say. I used to do designs for healthcare projects and the subject of supplemental ground rods and the GEC came up. We all agreed in the office that the GEC between the service neutral bus and supplemental ground rods do not have to be larger than what is noted in NEC 250.66(A). We used NEC table 250.66 to bond the building steel to the service which frankly makes more sense. But in every instance the AHJ makes us size the GEC based on NEC table 250.66. I guess what I need to do is get an official ruling from NFPA and settle it once and for all. Thanks again

The inspectors are dead wrong. I don't see any need for an official ruling, as action Dave pointed out in post #2 the wording is very clear.

 

[opes at askronald]

I know and I appreciate all the comments. If you lived in Florida you would understand where I am coming from. I fight with the plans reviewers and the building inspectors often about stuff like this and have gone to the state regulators about code issues being enforced by the local AHJ that is a life safety issue or simply wrong and they said the local AHJ is the law and I have to comply. I was told the AHJ has jurisdiction over the registered engineer and architect and my only recourse is to send a letter of protest to local code enforcement. This makes zero sense to me how a lay person can control what a licensed engineer does or doesn't do and not be held liable. If I had something in hand that exactly interprets the code from the horses mouth it will shut these people up, maybe. Thank you

 

[infinity]

I know and I appreciate all the comments. If you lived in Florida you would understand where I am coming from. I fight with the plans reviewers and the building inspectors often about stuff like this and have gone to the state regulators about code issues being enforced by the local AHJ that is a life safety issue or simply wrong and they said the local AHJ is the law and I have to comply. I was told the AHJ has jurisdiction over the registered engineer and architect and my only recourse is to send a letter of protest to local code enforcement. This makes zero sense to me how a lay person can control what a licensed engineer does or doesn't do and not be held liable. If I had something in hand that exactly interprets the code from the horses mouth it will shut these people up, maybe. Thank you

If they have the power to make up their own rules and enforce whatever they want then you'll have to do what they say. Doesn't mean that you cannot tell them that they're an idiot if they can't follow the written wording of the NEC.

 

[roger]

If they have the power to make up their own rules and enforce whatever they want then you'll have to do what they say. Doesn't mean that you cannot tell them that they're an idiot if they can't follow the written wording of the NEC.

And it's sad when idiots are supervised by idiots.

Roger