Auxiliary Ground Electrode, Grounding Electrode System, where is the line

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W@ttson

W@ttson

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The NEC has the requirement that if a ground electrode is present at the time of construction, then it MUST be used. This can be seen in 250.50 below.

250.50 Grounding Electrode System.
All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. If none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)⁠(8) shall be installed and used.

However, 250.54 says that if you add Auxiliary Grounding Electrodes, they do not need to comply with 250.50. See below:
250.54 Auxiliary Grounding Electrodes.
One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and (B)(4).

Here is a thought experiment I have been running through my head:

If I have my ground electrode system and I do all my bonding near my service (GEC, MBJ, electrode bonding jumpers, the works), but I also have some remote equipment, say on opposite side of a river, for whatever reason my heart desires, I want to drive a few ground rods there at the time of construction. I assume these to be auxiliary ground electrodes. I plan to install a large terminal cabinet on the opposite side of the river and have a ground bus bar that is 1⁄4 in. thick × 2 in wide x length as required. I plan to land my ground electrode bonding jumpers from the auxiliary electrodes to the ground bus bar in the terminal cabinet. I also plan to land my EGC from my feeder that traverses from one side of the river to the remote equipment terminal cabinet.

At what point do those auxiliary electrodes stop being auxiliary electrodes? Section 250.64(F) allows you to interconnect your ground electrode system electrodes via a ground bus bar. I assume since my interconnection across the river is through an EGC, that is what determines the auxiliary status of those remote electrodes? What if the EGC was of sufficient size to be a ground electrode bonding jumper, say due to upsizing as a result of voltage drop? Do those auxiliary ground rods stop being auxiliary? Does the fact that they were available at the time of construction mean that I need to treat them to meet 250.50?

Taking this thought experiment 1 step further:
Suppose you are wiring a detached garage. You install a 30A "subpanel" in the garage. You send a feeder of #10/3. You land your EGC in the panel from the feeder, you run a Ground electrode bonding jumper from 2 ground rods that you drove near the detached garage to the ground bar in the panel. Can it be thought of that the ground electrodes at the garage are auxiliary ground electrodes in the eyes of the main service ground electrode system (complying with 250.54 in reference to the main service GES) and the actual ground electrodes of the ground electrode system of the garage (complying with 250.50 in reference to the garage)?

If you read down this far, thank you. 😃
 
As pton pointed out auxillary electrodes have nothing to do with a grounding electrode system which is why the aren't required to comply with the rules for a GES.
 
W@ttson said:
The NEC has the requirement that if a ground electrode is present at the time of construction, then it MUST be used. This can be seen in 250.50 below.
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That applies to all structures with more than one circuit, not just the one with the service.

I assume these to be auxiliary ground electrodes.
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That is an incorrect assumption. The separate structure requires a "real" electrode system.

At what point do those auxiliary electrodes stop being auxiliary electrodes?
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The moment you left the main structure with a feeder to another, separate structure.

I assume since my interconnection across the river is through an EGC, that is what determines the auxiliary status of those remote electrodes?
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It is not. That would apply to extra, non-required electrodes within the same structure.

What if the EGC was of sufficient size to be a ground electrode bonding jumper, say due to upsizing as a result of voltage drop? Do those auxiliary ground rods stop being auxiliary? Does the fact that they were available at the time of construction mean that I need to treat them to meet 250.50?
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Doesn't matter, as made-electrode GECs are usually smaller than the feeders' EGCs.

They never were auxiliary electrodes, so no.

Yes, but not the only reason.

Can it be thought of that the ground electrodes at the garage are auxiliary ground electrodes in the eyes of the main service ground electrode system (complying with 250.54 in reference to the main service GES) and the actual ground electrodes of the ground electrode system of the garage (complying with 250.50 in reference to the garage)?
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From the service's point of view, you could say that.
 
Suppose one has two ground rods at a service. That is all you have for a GES.

Suppose one adds a third ground rod that is not needed but is compliant with all the requirements for being part of a GES. Is it an auxiliary electrode?
 
petersonra said:
Suppose one has two ground rods at a service. That is all you have for a GES.

Suppose one adds a third ground rod that is not needed but is compliant with all the requirements for being part of a GES. Is it an auxiliary electrode?
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If that third rod is connected to the first two, it is simply part of the grounding electrode system. Auxiliary electrodes are only connected to an EGC, and not to a GEC.
 
So let's say an auxiliary ground rod was connected to a subpanel in a home. The home is remodeled, and I redo all the electrical, and in the process I disconnect the auxiliary rod because I remove the subpanel completely. I also replace the service equipment. Am I required to bond the disconnected ground rod to the GES (if the GC doesn't pull it out of the ground for me)? ;-)
 
jaggedben said:
So let's say an auxiliary ground rod was connected to a subpanel in a home. The home is remodeled, and I redo all the electrical, and in the process I disconnect the auxiliary rod because I remove the subpanel completely. I also replace the service equipment. Am I required to bond the disconnected ground rod to the GES (if the GC doesn't pull it out of the ground for me)? ;-)
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No, you could just bond it to any circuit's EGC. Auxiliary ground rods don't need to be associated with a panelboard.

Cheers, Wayne
 
W@ttson said:
Suppose you are wiring a detached garage. You install a 30A "subpanel" in the garage. You send a feeder of #10/3. You land your EGC in the panel from the feeder, you run a Ground electrode bonding jumper from 2 ground rods that you drove near the detached garage to the ground bar in the panel. Can it be thought of that the ground electrodes at the garage are auxiliary ground electrodes in the eyes of the main service ground electrode system (complying with 250.54 in reference to the main service GES) and the actual ground electrodes of the ground electrode system of the garage (complying with 250.50 in reference to the garage)?
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I will say yes to the above.

Cheers, Wayne
 
ptonsparky said:
Auxillary ground rods would be those installed at equipment. CNCs came with requirements for rods at the machine. Code does not require them.

A GES is required at certain points. Those are not auxillary.
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They don't have to be at equipment. They can be at light poles, junction/pull boxes, etc. If it is connected to an EGC and not to the GES it is an auxiliary electrode.
 
LarryFine said:
You're welcome.

As a separate structure, the remote sub-panel location would require a legitimate electrode system.
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There is no building or structure on the other side of the river in my thought experiment. Say on the other side of the river was a large outdoor projector to shine at a mountain (getting pretty creative here). That is where the equipment is located, it is out in the open. I want to drive a ground rod there. I have a large terminal cabinet there. That terminal cabinet has a 1/4" thick bus bar. I land my EGC from my feeder there. I land my bonding jumper from the ground rod there.

There are two scenarios:
1. My EGC is just an EGC and does not qualify to interconnect the main GES and the remote ground rod.
2. My EGC does qualify as a ground electrode bonding jumper. Since it is landing on an approved location to interconnect ground electrodes, I believe that remote rod seizes to be an auxiliary rod.
 
don_resqcapt19 said:
If that third rod is connected to the first two, it is simply part of the grounding electrode system. Auxiliary electrodes are only connected to an EGC, and not to a GEC.
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Yea, I that is where I am trying to push the envelope. If I can make my EGC also be qualified as a ground electrode bonding jumper, I think I can make it not be an auxiliary ground electrode, but an electrode that is part of the GES. OR if it is convenient for me, do I just keep it as an auxiliary so that I don't have to comply with all of the other requirements that come along with real ground electrodes.
 
So the reasoning for my thought experiment, is because in the Engineering field there are specifications and requirements all the time that are on the side of - the more ground rods the better! Things can get pretty convoluted with many electrodes all over the place in an attempt to reach some sort of low ohmic value for the ground electrode system.

The NEC has certain requirements and those requirements are long met before even coming close to meeting the requirements of the jobs engineered specifications. My thought was that these auxiliary electrodes could be a way to ultimately lower the whole ground systems ohmic value without having to go into the tighter requirements of treating them as ground electrodes within the GES.

For example, if you are constructing a new structure, you have access to the CEE. That is your electrode. You have a water line, that is another one. You add a ground rod to supplement the water line. At this point you have 3 ground electrodes and I believe have met all requirements of the NEC regarding the quantity and ohmic value requirements. Now if the specification requires 1ohm ground resistance? You will need to keep added electrodes and tying them together as defined in 250.50 and 250.66. If you put some auxiliary electrodes throughout your distribution system, say at panelboards here and there and you use a clamp on ground resistance meter reading at the service location, I bet your ground resistance reading will be lower with those auxiliary ground electrodes connected than without them. They may not be connected all together via 250.66 sized electrode bonding jumpers, but they are at the end of the day interconnected via EGCs that ultimately end up at the main switch.

Then I thought to myself, well if the electrode is there in the beginning I usually make a big deal about making sure it gets added to the GES system (so to be compliant with 250.50) so I was thinking about when and where does the line get drawn? If I take my "Metal In-ground Support Structure" and connect it to a panelboard or a EGC somewhere, do I eliminate it from being required to be connected to the GES? After all, 250.54 doesn't require the auxiliary electrode to be a ground rod. It leaves it as "ground electrode".
 
W@ttson said:
There is no building or structure on the other side of the river in my thought experiment. Say on the other side of the river was a large outdoor projector to shine at a mountain (getting pretty creative here). That is where the equipment is located, it is out in the open. I want to drive a ground rod there. I have a large terminal cabinet there. That terminal cabinet has a 1/4" thick bus bar. I land my EGC from my feeder there. I land my bonding jumper from the ground rod there.
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If you have a sub-panel there, you have a feeder and need electrodes there.

If you only have a circuit there, you don't need but may install electrode(s).

There are two scenarios:
1. My EGC is just an EGC and does not qualify to interconnect the main GES and the remote ground rod.
2. My EGC does qualify as a ground electrode bonding jumper. Since it is landing on an approved location to interconnect ground electrodes, I believe that remote rod seizes to be an auxiliary rod.
Click to expand...
1. It does not need to be sized to act as a GEC; it's only an EGC. You may still have an electrode or more if you wish to.
2 You mean "ceases" to be? No, a conductor between structures, etc., is not a GEC. That's why a new electrode system must be established at a remote location.
 
LarryFine said:
If you have a sub-panel there, you have a feeder and need electrodes there.

If you only have a circuit there, you don't need but may install electrode(s).


1. It does not need to be sized to act as a GEC; it's only an EGC. You may still have an electrode or more if you wish to.
2 You mean "ceases" to be? No, a conductor between structures, etc., is not a GEC. That's why a new electrode system must be established at a remote location.
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Yes, "ceases".

I was trying to make a nuanced reference to 250.118(B) of the 2023 NEC (or 250.121 in earlier versions of the NEC):

2023 NEC version:
(B) Not Permitted.
The following shall not be used as equipment grounding conductors.
  • (1)
    Grounding electrode conductors
    Exception:
    A wire-type equipment grounding conductor installed in compliance with 250.6(A) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding conductor and a grounding electrode conductor.
  • (2)
    Structural metal frame of a building or structure

ENHANCED CONTENT
Equipment grounding conductors (EGCs) and grounding electrode conductors (GECs) have specific functions. GECs are required to be a wire- or busbar-type conductor in accordance with 250.62, whereas EGCs are permitted to be any of the types listed in 250.118. This exception permits a wire-type conductor to be used for both purposes if it satisfies all applicable requirements for both the EGC and the GEC and it does not carry current during normal operating conditions.

Earlier NEC versions:
250.121 Use of Equipment Grounding Conductors.
An equipment grounding conductor shall not be used as a grounding electrode conductor.
Exception:
A wire-type equipment grounding conductor installed in compliance with 250.6(A) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding conductor and a grounding electrode conductor.


The point was IF it became compliant with both EGC and GEC and is permissible to be used for both as allowed in the exception under 250.118(B) or 250.121 (depending on year), what happens to the classification of that electrode.

Also, I said that it is a large terminal cabinet, one of these: https://hoffman.nvent.com/products/free-stand-single-and-dual-access-type-4x

Its not a building or a structure. I do not believe the requirements of 250.32 apply. Unless the terminal cabinet is considered a structure.
 
If the terminal cabinet is 'large' as you say then it could definitely be a structure. The definition of structure is extremely broad and basically up to the AHJ. Arguably any size cabinet could be called a structure if someone wants to call it one.

I don't understand the point of all this. What is your motivation to claim the electrode at the remote location is auxiliary or not? The code requires the GES at the remote structure (if that's what it is) if fed by a feeder, etc. If the code does not require it and it's only connected to the circuit EGC then it's auxiliary. If people want to put further requirements in job specs then that's their own perogative.
 
Do you consider its supply to be a branch circuit or a feeder?

If it's a branch circuit, no electrodes are required, but are permissible.

If it's a feeder, an electrode system is required.

In neither case is the supply's bare wire a GEC; it's only an EGC.
 
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