ECN Forum Forums Code Related Discussion NEC & other Code issues Grounding rod for outbuilding branch circuit?

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)

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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.