250.32(A) Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the non-current-carrying parts of equipment. For the porpose of this section, a multiwire branch circuit shall be considered as a single branch circuit.

Question: Can that excepted branch circuit feed a panel, or is a grounded rod always required when a panel is installed? Article 210.2 specifically lists branch circuits feeding panelboards, so does a panelboard feeder count as a branch circuit?

[This message has been edited by SteveFehr (edited 10-23-2006).]

In a word, Steve....NO.

There are "services." There are "feeders." And, finally, there are "branch circuits".

A wire supplying an overcurrent device is a feeder, not a branch circuit.

Then why does 210.2 list switchboards and panels as specific kinds of branch circuits?

I'm not seeing anything in 210.2 that identify or list switchboards or panelborads as being fed by a branch circuit. I would agree with Reno on the hierarchy - Service> Feeder> Branch circut

Table 210.2 (referenced to by 210.2) near the bottom.

I see what you are talking about now. I was looking at 210.2 instead of Table 210.2. The table references 408.52 having to do with a circuit(s) that would be used for protecting instrument devices associated with a panelboard. The panelboard or switchboard would have in addition to this circuit, a feeder or service conductors that would be the actual feed for the panel or switchboard IMHO

ahh, that would be the difference then!

Next loophole. So, an electrode is required at the outbuilding- NEC 250.52(A)(5) and 250.32(G) permit a ground rod to be used, but do not set any restrictions on placement. (Other methods are similarly unrestricted) 250.58 requires seperate services and feeders to share a common electrode, explicitly allowing multiple services and feeders to share a common electrode. 250.64(C)(3) permits connections to busbar to be used vice a single continuous conductor. Would this not allow the outbuilding subpanel to ground to the main building electrode to satisfy 250.32?

[This message has been edited by SteveFehr (edited 10-24-2006).]

Steve- In 250.32 it tells us a grounding electrode is required per 250.50. When we go to 250.50 it tells us that all the electrodes that are present at that building or structure are to be tied together and if non are present we need to install one or more. I take that to mean that the Grounding electrode must be at or in the building or structure it serves.

Steve, separate electrodes simply must be connected to the grounding network; supplimentary electrodes, however, require a full size grounding electrode conductor.

In other words, if your 'ground wire' were #6AWG, and run without splicing all the way back to the service disconnect, you MIGHT have a hook to hang the argument on.

BUT- such a 'hook' would be a creature of grammar, not engineering. Remember, the 'ground rod' is there for lightning, and not for clearing faults. A separate structure is a separate target. Wouldn't you want to keep the lightning out at the shed?

Now, we can split hairs all day about what is, or is not, a separate structure. Without trying, I can think of several layouts that blur the line. I think the code simply uses the 'one branch circuit' rule as a threshold, a way of saying 'more electric than that, and it is, without a doubt, a separate structure.'

A 12x12' shed, in the shadow of a 2-story house and surrounded by trees? Seems as though the 12/2 feeder feeding a 2-circuit panel with two 15A circuits aught to be plenty with just the #12 Cu ground.

I do have a problem with this related to several real sites, too. In commercial/industrial construction, we generally have a power vault on a corner of the building, often with switchgear, generators and UPS. What 250.32 says is that this is fine so long as that CMU wall is shared, but move that power room 5' further away to create a fire gap, and suddenly, I've got a real grounding problem with every single one of my subpanels.

Granted, I prefer to use multipoint grounds as much as possible, but there are some cases when a 250.50 ground connection is impractical, otherwise unnecessary and very expensive.

[This message has been edited by SteveFehr (edited 10-24-2006).]

Steve, although not exactly like your vault, i have a similar situation with my house. The service disconnect is in the garage (200a panel) with a 150a feeder to the house 13' away. My ground electrode system is between the two. It is really only one system but one of the rods is under the meter base at the garage and the other (2) are under the LB where the feeder enters the house. They are tied together underground with a bare #2 (in the same 24" trench as the raceway). One might argue I only have one ground electrode system for 2 buildings. I don't see the problem.

If the 2 buildings are tied together with a common foundation I think they are considered to be one building. On the other hand if the two buildings only had a roof or car port type connection, my understanding they would be considered two buildings. This becomes an issue sometimes and a building inspector explained it to me this way. Makes sense to me.

Coming up in the 2008 code ,equipment grounding conductor will be required to be ran with the circuit conductors

I am confused. I dont do residential. But I helped a buddy out whou built a three car grage with a second story (game room)about 75' from the house. I ran conduit from the house service, to a 100a panel in the garage. Ran #2 SER in the conduit.

I than drove a ground rod, right outside the garage where the conduit came up, and bonded my garage panel (like a service) and ran a #6 grounding conductor to my electrode.

The inspector told me to disconnect the ground rod and use the grounding conductor in the SER for the ground only.

I did what he said, but do not agree.

Whom is right?

Not the inspector. Plus I find it hard to believe he allowed SER in conduit. Not listed for use in conduit.

If you read this thread you can see how inspector and contractor alike will say that your grounding electrode at the second building was accurate. You should have floated the neutral and fastened the wire from the grounding buss to the rod(s).

The neutral must be floated at the garage. NEC normally requires a grounding electrode for a detached garage, but the exceptions do allow you to use the main building's grounding electrode if the ground wire is continuous and spliced in the right way.

So, I don't think what the inspector told you is illegal, but there's no reason he should have had you disconnect the ground rod.

In either case, the neutral bus should be isolated & ungrounded in the garage panel, lest you couple current onto the ground wire connecting the garage subpanel to the main panel in the house.

Steve I need some code references here. When I read in the NEC 250.32 I don't see any exceptions allowing a second building to be without a Grounding Electrode unless it is a branch circuit and not a feeder supplying the second building. And I'm not reading anything in the NEC allowing the use of the Grounding Electrode at the Main building becoming the Grounding Electrode at the second building if it's "spliced in the right way" what am I missing?

I have a question about the 12' X 12' shed scenario. Isn't the minimum allowable feeder size #10? Since it was mentioned that it's feeding TWO overcurrent devices, doesn't that make the branch circuit feeding the shed become a feeder, thus rules for feeders and sub panels would apply? Hey, I am just asking.

I did the same thing with my shed, well sort of. I ran a 1" PVC with four THWN #6, to a 12 circuit sub panel with a 60 amp main breaker (kit). There was a ground rod lying on the ground that I just happened to have sitting there. The first thing the inspector said to me was "what's that rod for?" I explained that it had nothing to do with my sub panel and that I understood that the sub panel had to be fed with a separate EGC. He made me promise that I wouldn't come back and drive/connect it later as he signed off on the job.

In a recent continuing education course I took to maintain my license, we learned that a separate EGC must be provided for sub panels IF there is any chance that any form of other metallic connection between the buildings exists (water, gas, telephone, CATV), etc. If there is no metallic connection, then the sub panel may be wired like a service, with a bonded neutral to rods, etc.

I still stick with the separate EGC since you can't control someone coming in after the fact and adding a metal water line thus turning your installation into a violation.

On another note, SER in a pipe underground is a definite no-no. I don't know how that one passed inspection.


[This message has been edited by EV607797 (edited 11-28-2006).]

George, if you read up this thread a little ways, you'll see that even though a GEC is required for the garage, it doesn't need to be located at the garage, and can share the house rod.

250.64(C)(3) permits connections to busbar to be used vice a single continuous conductor. The grounding conductor run between the house and garage, and house's GEC thus satisfy 250.32.

EV607797,

I ran a 20A GFCI-protected circuit to my shed, which let me run it just 12" deep in PVC, so as to avoid trenching deeply into my septic field. Really, it should only be a single branch circuit for what I need (lights and receptacles), but I had previously wired it up with a panel which I had installed about 5 years ago with the intent of putting in a 240V 30A circuit for heat, AC and a bunch of shop tools. Of course, I never got around to actually running the feeder, and instead just spliced on a 3-prong plug into a backfed 15A breaker and plugged it into an extension cord... So, it's WAY better now!

NEC allows 20A feeders, but it can only have 2 circuits on it. So, I rewired it for 2 circuits.

I know I'm in violation of NEC as I did not drive a grounding rod, and the ground conductor is spliced in the GFCI box, violating 250.64(C). But the AHJ here didn't so much as bother to open the shed door when he inspected my addition, letalone look that hard at it, so I get the feeling they just don't care.

This brings up an interesting question. Isn't there a dual rated SE/USE cable?
I thought I heard about flame retardant, UV protected USE.

That's a good question. I recently asked the AHJ in my area about that and they said NO. SER is not rated for wet locations, as in within pipe underground but OK for damp locations. My understanding is that for a piece of SER running from an outdoor disconnect along a wall will be OK.

I agree. Anyone else have any thoughts on this? My guess would be that the cable consists of type XHHW conductors so it falls into a gray area; perhaps the outer jacket of the cable comes into play in making this determination. I really wouldn't do this kind of installation anyway, so I never even looked into the code book about it.

Out of UL White Book:
Steve- I'm not in agreement with your Buss-Bar anology for the second building. We need a grounding electrode for a second building

Article 215 doesn't give any minimum wire gauge for a feeder, only that it be large enough to carry the load.
As for the tool shed that needs 30a. It needs to comply with the feeder rules if there is to be mopre then one circuit. Either single circuit or multiwire branch circuit.

This is frustrating, I've been up and down NEC twice now, and can't find the paragraph that says a 20A feeder was OK but limited to 2 branch circuits, I know I didn't just imagine it! All I can find is 225.39 mandating feeder or branch circuit disconnecting means rated for a minimum of 30A- no mention of minimums for the OCP or the cabling with respect to the number of branch circuits, just that the disconnecting means are rated for at least 30A if there are 2 branch circuits. I'm pretty sure any circuit breakers used as a service or local disconnect are going to be rated for at least 10kAIC. Or, failing that, at least an interruption capability of 400% or so, thus well exceeding the 30A minimum. I believe this section of code relates more to simple mechanical switches- light switches and HVAC disconnects and the like, and doesn't apply so much to breakers. Does NEC place any actual restrictions on the feeder circuit itself? Again, I'm pretty dang sure I saw 20A somewhere in NEC, but I'm beating my head to find it!

225.39 Rating of Disconnect. The feeder or branch-circuit disconnecting means shall have a rating of not less than the load to be supplied, determined in accordance with Parts I and II of Article 220 for branch circuits, Parts II or IV of Article 220 for feeders, or Part V of Article 220 for farm loads. In no case shall the rating be lower than specified in 225.39(A), (B), (C) or (D).

(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the feeder or branch-circuit disconnecting means shall have a rating of not less than 30 Amperes.

-Again, this appears to be referring only to the rating of the disconnect means, and not the size of the feeder circuit itself. Article 215 gives other criteria for sizing the feeder circuit; the number of branch circuits is not part of that criteria. (A 12x12 shed would require just 432VA)

--------------------------------------

As to using the bus bar for grounding- I've yet to see anything that says it's illegal to ground a panel with a grounding electrode conductor spliced using a bus bar. NEC specifically allows it, and I'm pretty sure places no length or proximity restrictions on the conductor- if it does place a restriction, I've yet to see it.

[This message has been edited by SteveFehr (edited 11-29-2006).]

Steve- Been thinking about this issue today in my travels and you said:

I read that in NEC 250.50 the words "at each building served" and this tells me the electrode must be at each building. We can't say run a #6 cu wire from the second building and bring it back to the first building. IMHO


[This message has been edited by George Little (edited 11-29-2006).]

The only way I could see this is if you had the rod in the space between the buildings and ran the 2 building GEC directly to the rod. That is probably more work that just driving one.

I've been pondering this, too. Trying to think logically, what best engineering practice would be. If bonded/ground properly, either way would be safe for people. Driving a ground rod at each outbuilding would be better for lightning protection, though, as the bolt would be driven to ground with less impedance. For a garage, this is appreciable, but not so much for a shed surrounded by taller buildings and trees. For both a garage and a shed, the new local ground rod would be a better design, but I'd consider both to be acceptable unless there was substantial risk of a lightning strike.

As to your quote, it appears to me that 250.50 only refers to all grounding electrodes that are present at each building or structure served be bonded together. It does not imply that a grounding electrode must be present at the structure, just that if multiple ones are used, they need to be connected.

[This message has been edited by SteveFehr (edited 11-29-2006).]

Read all of 250.50, including the last sentence: "Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(7) SHALL be installed and used."

Well, that brings us back around to my original argument- that article 250, specifically including 250.50 and 250.52(A)(5), places no restrictions on the distance from the panel to the grounding rod; there are plenty of installations where the soil right up against the building is unsuitible for grounding and the ground is made a good distance away. There is quite simply nothing prohibiting use of the house grounding rod as the outbuilding electrode, if the conductor is sized properly and spliced IAW 250.64(C).

[This message has been edited by SteveFehr (edited 11-30-2006).]

I disagree. 250.50 says, "All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are PRESENT AT EACH BUILDING OR STRUCTURE SERVED shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(7) shall be installed."
At each building or structure means exactly what it says. If you feed a detached structure from another structure there must be one or more of the grounding electrodes described in 250.52(A)(4) through (A)(7) at each structure. This is exactly what 250.50 requires. I would like to know how you would justify utilizing the grounding electrode located at one building as the grounding electrode for a separate structure and still satisfy the requirement of 250.50. I don't care if the second building is only 1 foot away. If it is not attached, it is a separate structure.

Could you quantify the distance that "present" means? 1ft? 2ft? 20ft? 50ft? 500ft? NEC deliberately chose not to quantify this distance. They chose instead to dictate wiring methods and minimum sizes instead. So long as those methods and sizes are adhered to, the installation is safe and legal, regardless of it's "present" 1ft from the building or "present" 50ft away and shared with the primary structure.

I contend that "present" simply means that it exists at the site where each building is, not that it be located along the edge of the foundation.

[This message has been edited by SteveFehr (edited 11-30-2006).]

While the NEC doesn't give a measurment of the proximity of a grounding electrode to a building or structure, it does state "present at each building or structure" indicating more than one single grounding electrode. It says one of the electrodes at each building or structure, not one grounding electrode per parcel of land. A distance of 1-6 feet would be reasonable and as was stated in an earlier post, if that was the distance between the 2 buildings you're talking about I think it would be reasonable. But 50-500 feet of distance I believe is clearly not "at the building or structure". By your reasoning, why don't we just use the PoCo's incoming neutral? It's grounded to the copper on the pole which consists of a butt wrap 6-8' deep on the bottom of the pole and is probably a better ground than any 2 driven rods. Because it's not "at each building or structure", that's why. The earth is considered to be at zero potential. In some cases, the grounding electrode serves to ground the electrical system. In other instances, the electrode is used to connect noncurrent carrying metallic portions of electrical equipment to the earth. In both situations, the grounding electrode attempts to maintain the electrical equipment at the earth potential present at the grounding electrode. Earth potential can vary over a distance of, say 10'. What good does it do to maintain earth potential of one building at another, detached building? You would likely have objectionable current on the GEC at the second building. To appreciate and better understand the purpose and function of grounding electrodes, the Soares Book on Grounding is the best place to learn.

Fred- Here's your green sticker. I think you expressed the intent of the code and I applaud you (clap clap)