# of ground rods required at a residential detached storage building?

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suemarkp

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Kent, WA
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Retired Engineer
Really, what code book are you reading? I don't see that at all in 250.50 which talks about using all the electrodes present.

NEC 250.32 says each structure shall have a ground electrode or ground electrode system installed in accordance with...

Sinking one rod would meet the requirement of 250.32. I don't see how picking up your aux rod from another system would violate that.
 

hurk27

Senior Member
Really, what code book are you reading? I don't see that at all in 250.50 which talks about using all the electrodes present.

NEC 250.32 says each structure shall have a ground electrode or ground electrode system installed in accordance with...

Sinking one rod would meet the requirement of 250.32. I don't see how picking up your aux rod from another system would violate that.

My bad as I was remembering the 2002 250.50 wording:
If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system.

As you can see in the red kind of says the electrodes we use have to be "at each building or structure served" this was where I was coming from, but I see it was reworded in the 2008. but still kind of says the same thing?:?

To me (and I been wrong before) this tells me its not ok to grab an electrode from another building and use it?
 
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suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
As you can see in the red kind of says the electrodes we use have to be "at each building or structure served" this was where I was coming from, but I see it was reworded in the 2008. but still kind of says the same thing?:?

To me (and I been wrong before) this tells me its not ok to grab an electrode from another building and use it?

I don't see having to use all electrodes present at a building as prohibiting using electrodes elsewhere too (but you certainly must use all the electrodes at the building). Where this two rod thing really gets me is if you have a detached structure or even just a pole/pedestal that is 10' from the main building. Seems kind of silly to mandate 4 rods all 6' from each other but yet only allowing two per building (no sharing). Wouldn't three rods provide more protection than two?

In the case of two buildings far apart, I don't think having the second rod 50 to 100 feet away is going to be very effective. But I still don't see any code prohibiting it.
 
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iwire

Moderator
Staff member
Location
Massachusetts
I agree with hurk27s view on this.

But also new for the 2011 NEC

250.121 Use of Equipment Grounding Conductors. An
equipment grounding conductor shall not be used as a
grounding electrode conductor.
 

renosteinke

Senior Member
Location
NE Arkansas
Well, I see that some folks continue to assume that I'm doing things wrong, etc. Well, that's far easier to assert than to support your own bias with the code. Maybe I wasn't clear enough, so I'll try to develop (explain) my reasoning, using smaller words and shorter sentences.

I'm not going to reopen the "25 ohm" debate. This was made irrellevant when the 2011 code added 250.53, which mandates that a single rod be supplimented. Yet, this addition has further relevance, and I'll return to it later.

Let's first look at the the requirements for services. Our GEC has to go back to the first OCPD, where we bond the neutral to the GEC. After then, we keep the two completely separate. This works fine, at least when there is only one building. The question arises: what to do when there is a second building served by the same service?

At one time it was common to treat the feeder to the second building as if it were its' own service. These days, for all practical purposes, we can't do that anymore. Instead, we are required to run a ground wire with the feeder, and to continue to keep the 'grounds' separate forn the neutral.

As a reminder, there are two types of "grounds.' There are the equipment grounds, which help breakers trip, and there is the GEC- the wire from the ground rod.

The next question we need to ask is whether ANY 'ground rod' is required. I'd like to point out that the NEC does not require that any building have a 'ground rod.' One could - and probably would- rebuild the World Trade center without there being a single ground rod anywhere. Think about that for a moment.

We are required to have a grounding 'electrode,' not a 'rod.' A 'rod' is but one of the alternatives if none of the other grounding electrodes are used. If our detached building has a slab, one might easily make that slab into a concrete-encased electrode ("Ufer") and not need any ground rod at all. If the detached building has a metal water line, that might be the only electrode we need (as the pipe is not under the control of the water department).

If someone wished to suppliment the water pipe (or any other electrode) with another electrode, by banging in a rod .... I don't see any requirement that they use two rods. Instead, I see 250.53, which requires a single rod to be supplimented.

Now, let's look at 250.53 in greater detail. How do we suppliment the single rod? Well, 250.53(2)(5) says we can bond it to any grounded service enclosure. That sounds a lot like the panel for the detached building to me.

This might appear as if we are using the green wire of the feeder as both the 'grounding electrode conductor' and the 'equipment grounding conductor.' I submit that the NEC needs to clarify this point, as it's my view that the 'equipment grounding conductor' ends with the branch circuit. As I see it, the green wire with the feeder is simply a 'grounding conductor.'

The alternative to accepting my understanding is to not tie the ground rod into the panel at all, but to instead run a completely separate wire from our new ground rod to a ground rod at the first building.

What about the size of the green wire we run with the feed? Well, we size that by 'neutral' rules, which gives us a larger wire than if we were to size it by 'GEC' rules. I will concede that it's possible that a small panel in the detached building might have a feeder smaller than #6, so it is possible that the green wire will be smaller than the #6 that the NEC might require for the GEC of the main service.

That might present us with a problem. As long as the GEC for the detached building is large enough to serve the entire service, I see the grounding electrodes of the two structures as forming one single grounding network. In electrical terms, the two are not 'detached' at all.

Unorthodox view? I don't think so. After all, this is exactly what we've been doing with swimming pools, and the area around them, for years. Indeed, if you compare the 'equipotential plane' requirements, you will find that it also qualifies as a grounding electrode.

To sum up my view .... as long as that green wire for the feeder is #6 .... the rods at the separate buildings are part of the same grounding system, and fulfill any need there might be for a second electrode. Just think of them as being more -way more than- six feet apart.
 

iwire

Moderator
Staff member
Location
Massachusetts
To sum up my view .... as long as that green wire for the feeder is #6 .... the rods at the separate buildings are part of the same grounding system, and fulfill any need there might be for a second electrode. Just think of them as being more -way more than- six feet apart.

You are still mistaken and this has been made very clear in the 2011 NEC



250.121 Use of Equipment Grounding Conductors. An equipment grounding conductor shall not be used as a grounding electrode conductor.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
250.121 Use of Equipment Grounding Conductors. An equipment grounding conductor shall not be used as a grounding electrode conductor.

Hmmm, that's a new one I haven't seen. But is an electrode bonding conductor a GEC? Even if you say no, I think 250.121 is putting even more intent on keeping the GES at each structure separate.
 

LWFLASH

Member
Location
Colorado
Supplemetal Electrode Required

Supplemetal Electrode Required

Excuse me, I have read the post in this Forum questions it eludes me as to why would you even need a ground rod at a garage if you only had one branch circuit for the Light Fixture, Receptacle, and Garage door opener. The wire itself carries the ground back to the panel.
Is it now the contention of the code to be forced to install a 30Amp 1 Phase Disconnect to shut off one 15Amp Circuit to the garage, as well as drive another ground rod or use another approved grounding method. If this is the case I need to retire and get out of this business it is becoming insane.
The code is very presice about grounding on seperate buildings however does that building have a panel being fed from another panel with a branch circuit or a set of feeders?? If so it requires grounding re-established at the seperate building. If not ???????
I could use some input here. Thanks
LWFLASH
Denver, CO:ashamed1:
 

iwire

Moderator
Staff member
Location
Massachusetts
If you run just a single branch circuit* to a separate building or structure you do not have to add or connect any additional grounding electrodes.


(*A muiltiwire branch circuit can count as one)

If you run two or more branch circuits, or a feeder to a separate building or structure you do have to add or connect additional grounding electrodes at that new location



250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s).

(A) Grounding Electrode.
Building(s) or structure(s) supplied
by feeder(s) or branch circuit(s) shall have a grounding
electrode or grounding electrode system installed in
accordance with Part III of Article 250. The grounding
electrode conductor(s) shall be connected in accordance
with 250.32(B) or (C). Where there is no existing grounding
electrode, the grounding electrode(s) required in 250.50
shall be installed.


Exception: A grounding electrode shall not be required
where only a single branch circuit, including a multiwire
branch circuit, supplies the building or structure and the
branch circuit includes an equipment grounding conductor
for grounding the normally non–current-carrying metal
parts of equipment.
 

jumper

Senior Member
You also do not need a 30 amp disconnect for a single circuit. I think a MWBC is counted as one.

225.39(A) One-Circuit Installation. For installations to supply
only limited loads of a single branch circuit, the branch
circuit disconnecting means shall have a rating of not less
than 15 amperes
 

renosteinke

Senior Member
Location
NE Arkansas
Iwire- I might very well be 'wrong.' If so, then the OP was on the right track is assuming he might need more than one rod.

I still see a difference between the ground wire for a branch circuit and the ground wire that accompanies a feeder. If you 'can't' consider it as a means to bond the various electrodes together, then Article 250 still need a LOT of work. (Just consider what happens when we ground a transformer to building steel). One might go so far as to say 250 is beyond editing, and needs a complete re-write.

That, however, is a topic for another thread.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Iwire- I might very well be 'wrong.' If so, then the OP was on the right track is assuming he might need more than one rod.

I still see a difference between the ground wire for a branch circuit and the ground wire that accompanies a feeder.
How are they different? They are both intentional low impedance paths for clearing faults.

If you 'can't' consider it as a means to bond the various electrodes together, then Article 250 still need a LOT of work.
Since earthing is for a completly different reason than bonding it does make some sense (there could be some exceptions IMO) to keep the two seperated except for where they connect at the Main Bonding Point.
(Just consider what happens when we ground a transformer to building steel).
Which has nothing to do with fault clearing, it serves the same purpose as a GE.
One might go so far as to say 250 is beyond editing, and needs a complete re-write.
I don't see an issue with it the way it is, I think the biggest problem is that Earthing and Bonding are two seperate animals and many have some confusion with that.

Roger
 

paul

Senior Member
Location
Snohomish, WA
Hmmm, that's a new one I haven't seen. But is an electrode bonding conductor a GEC? Even if you say no, I think 250.121 is putting even more intent on keeping the GES at each structure separate.

Mark,

At this time, due to budget restraints, WA state is not adopting any new code changes for building trades. We will continue to be under the 2008 for awhile. Normally we would already have adopted the 2011 code.
 

gndrod

Senior Member
Location
Ca and Wa
2011 bypass

2011 bypass

Mark,

At this time, due to budget restraints, WA state is not adopting any new code changes for building trades. We will continue to be under the 2008 for awhile. Normally we would already have adopted the 2011 code.

It really is a challenge to write about applicable current codes and not confuse a reader that needs to stay focused on the local adopted code cycle. (I.e. Adopting the usage of the new AFCI receptacles for remod extensions instead of a complete new AFCI BC. I believe there is leeway in some cases.)
 

RichardR

New member
Location
Lebanon, PA USA
Exception to article 250.32

Exception to article 250.32

There are exceptions to Article 250.32. Read your Nec 2011 book on page 232 & 233 and also refer to exhibit 250.18 where it shows an installation not requiring a GES and why it is not required. Some of these questions are not warranted if the Nec is consulted prior to asking the question. However, it appears that some don't have a Nec book in their possession and in my opinion it sure be a requirement tha t if the person is an electrician he should carry one. There is some confusion in the fact that some appear to shoot from the hip rather than consult the Nec before answering questions. However, there are some who give reference to Nec articles and those most times are quality answers. I also believe that Mike Holt should clarify the correct answer to these questions since it is his forum!
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
I also believe that Mike Holt should clarify the correct answer to these questions since it is his forum!
If Mike did chime in his opinion would not constitute a formal interpretation, his answer would hold no more official weight than those who haven already given a correct answer or even those who have not given a correct answer. :)

Roger
 
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