Hi All. When installing a sub panel at a garage using 4 6 awg's and driving a ground rod bonding it to the grounded conductor at the sub panel, can this ground rod be considered part of the grounding system at the house? Would it still be necessary to drive a second rod at the detached structure when there are 2 more at the house service location? For the longest time I have driven only 1 untill a recient inspection failed for not having a second at the garage. Am I missing something? I want to be sure I install them correctly.
Mark- It appears that we may have a couple of issues with your question. My answer would be we need an electrode at the separate building based on 250.32 and this points us to Part III and 250.52 now an electrode consisting of a rod needs to be <25 ohms based on 250.56 and if not less than 25 ohms, most contractors will simply add another rod. Now for the second issue. You stated that you ran 4 number 6 AWG conductors to the garage leading me to think that you ran an equipment ground wire along with a "Grounded" conductor and 2 ungrounded conductors. If this the case, you would be "floating" the grounded conductor by leaving the bonding screw out of the neutral bus and your # 6 equipment grounding conductor along with your conductor going to your rod(s) will be terminated on a grounding bus that is fastened to the enclousure. (assume metal enclousure)
#96090 - 11/02/0511:30 PMRe: 2 Ground Rods at Garage
Thanks George, I understand. Driving a second rod is no big deal. Especially with a Hilti rod attachment. I misunderstood the code section.(Go figure). When driving grounding electrodes at a separate structure we DO NOT bond the neutral bar to the equipment ground when wunning 4 wire feeders. Then it may have been simpler to run 3 wire and bond at the subpanel. Thanks
P.S. Good segment at the RECI Update. Somehow the whole course didn't seem as boring as it used to be. Maybe I'm just getting older.
#96091 - 11/03/0512:30 PMRe: 2 Ground Rods at Garage
From a code perspective, I think you can make a good case that a second rod anywhere on the property that is bonded to the primary rod with an appropriate sized wire should be sufficient for the "augmenting" rod. This augmenting rod is required when you can't get 25 ohms from the primary rod. The only restriction i see in the code is that the rods must be at least 6 feet apart. The #6 EGC in your feeder would be sufficient bonding for a rod on any size of service or feeder.
I tried this once, and the inspector wouldn't buy it. I had enough other issues to challenge him on that I didn't press it, but I think the concept was just foreign to him.
Mark Kent, WA
#96092 - 11/04/0510:14 AMRe: 2 Ground Rods at Garage
Originally posted by George Little My answer would be we need an electrode at the separate building based on 250.32 and this points us to Part III and 250.52 now an electrode consisting of a rod needs to be <25 ohms based on 250.56 and if not less than 25 ohms, most contractors will simply add another rod.
Let’s take a closer look at 250.32
250.32(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 250.50. 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.
The only referral to a grounding electrode found in 250.32 is to 250.50. In 250.52 we are instructed to install one of the electrodes found in 250.52.
No where in either section 250.50 or 250.52 does it refer us to 250.56 for 25 ohms or less nor to 250.53 for the supplemental electrode for a metal water pipe.
I have submitted a proposal to have the reference to 250.50 removed and replaced with (Part III of 250). As presently worded only one rod at a second building can be enforced.
[This message has been edited by jw electric (edited 11-04-2005).]
#96093 - 11/04/0512:21 PMRe: 2 Ground Rods at Garage
JW Electric - Seems kind of nit-picky. With that reasoning, I think you could say you don't have to scrape any non conductive coatings off the rod (250.53A), don't have to drive it deep enough or straight in (250.53G), an aluminum GEC could be in the earth (250.64A), don't have to protect the GEC from damage (250.64B), ...
This isn't rational. To me, once you've been forced to install a ground electrode system as in 250.50, all of the sections of 250 Part III should be applicable. That being said, I think your code proposal does add clarity and reinforce what we all "know".
[This message has been edited by markp (edited 11-04-2005).]
Mark Kent, WA
#96095 - 11/04/0509:15 PMRe: 2 Ground Rods at Garage
Thanks All, Great responses. I, too think that it is unclear. Which is why I wonder why I was not cited from other municipalities before. Driving a second rod is no big deal. Hopefully it will be clarified in the next code cycle as JW has proposed. Blessings, Mark
#96096 - 11/04/0511:34 PMRe: 2 Ground Rods at Garage
JW- I was using the '02 code because that's the code we are on in Michigan. I looked in the '05 at your reference and if I'm going to agree with you then I guess the code words at 250.54 are ridiculous.