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Old 10-24-2008, 03:26 PM   #1
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I am getting conflicted information on the topic of wiring a sub panel to a remote building. 1. Some say to use three wires (2 conductors and 1 neutral) from the main panel run to the sub. Run a ground wire from the sub to an 8' ground rod. 2. Others say to run three wires with a ground from the main panel to sub, both ground wire and neutral wire connected to the neutral bar in the main, and then seperated in the sub panel. Ground wire to a ground bar and neutral to an unbonded neutral bar. 3. Some say the same as #2 but, with the addition of an 8' ground rod also connected to the sub panel ground bar. Which is best? Any help is huge!! I shut my eyes and all I see is balls of tangled copper wire of all sizes and types!
I built a work shop to roast coffee from. I installed a square D QO box. 100 amp with main breaker. I just finished digging my trench 16" deep, and ran my conduit. I purchased 4 runs of #6 thhn 100' in length. Sub panel is 75' from the main panel. Main is 200amps. I am installing 60amp double pole breaker in the main to feed the sub panel. I will use the 100 amp breakers in the sub as my safety disconnect. I am ready to run my wires through the conduit, but want to know if it's best to run three or all four wire setup? Thanks for your reply, Brian

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Old 10-24-2008, 03:51 PM   #2
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Four wires, in conduit, 18" deep, ground bar in panel bonded to can. Unbonded neutral. TWO 8 foot ground rods, flush to the ground, at least 6 feet apart, #8 copper between them and to the ground in panel.

This the required method. Older codes allowed a three wire feed, but it is not a good idea. In either case you are still required to have ground rods.

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Old 10-24-2008, 04:12 PM   #3
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Ok! Sounds good! Two ground rods it is! Thanks, Brian
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Old 10-24-2008, 04:14 PM   #4
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And four wires from the main!
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Old 10-24-2008, 04:17 PM   #5
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can a use a piece of the #6 thhn for my ground rod wire. I will have a bunch left over. Or is it better to use bare copper? Thanks again, Brian
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Old 10-24-2008, 07:40 PM   #6
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can a use a piece of the #6 thhn for my ground rod wire. I will have a bunch left over. Or is it better to use bare copper? Thanks again, Brian
Has to be green or bare. Stip it and you should be OK.
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Old 10-24-2008, 07:47 PM   #7
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Has to be green or bare. Stip it and you should be OK.
Should be fine with out going through the hassle of stripping all the insulation off the wire just for a ground rod....
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Old 10-24-2008, 08:04 PM   #8
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Should be fine with out going through the hassle of stripping all the insulation off the wire just for a ground rod....
"should" is not the issue. rules are rules.
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Old 10-24-2008, 08:07 PM   #9
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I have to question the " two " ground rods . That might just be a local code rather than NEC . I'm from south La. and one ground rod is all they require here . More won't hurt
And definitely , I would go with four wires . Two hots and one( white ) to isolate the neutrals ( not bonded to the panel ) and one for the grounds only and to bond with the panel . ( green ) . Rather or not it is required in your area , you already purchased them anyway .
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Old 10-24-2008, 08:29 PM   #10
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"should" is not the issue. rules are rules.

I believe an insulated #6 green grounding wire is acceptable for use in connecting to a ground rod(s). It is my understanding that only the water pipe bond has to be bare copper wire; and of course the wire must be un-broken the entire distance from panel to the bond point (no connections or splices).

Read the quote from InPhase on the issue of two ground rods.... (this was found in another thread here in the forum)

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...IF you can verify that the electrode has a resistance of 25 ohms or less to earth. But the code says that if we can't meet the 25 ohms, then another electrode shall be installed, with no further requirement for resistance verification. So electricians started driving two rods. It was easier than having a single rod verified.

If you put it in a metal raceway, then you need to connect it to both ends of the raceway.
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Old 10-24-2008, 08:49 PM   #11
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The color of the wire for the grounding electrode is not addressed, as far as I know, in the code. The only wires that have to be green or bare are equipment grounding conductors.
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Old 10-24-2008, 08:50 PM   #12
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By code the ground wire can be green or bare . Taped #6 is technically not allowed , if you want to nit-pick . Bare wire through a metal raceway has to be bonded on both ends ,but with PVC it doesn't matter . You are probably right about the 25 ohms thing , but here in Louisiana , it is not an issue .
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Old 10-24-2008, 09:01 PM   #13
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I believe an insulated #6 green grounding wire is acceptable for use in connecting to a ground rod(s). It is my understanding that only the water pipe bond has to be bare copper wire; and of course the wire must be un-broken the entire distance from panel to the bond point (no connections or splices).

Read the quote from InPhase on the issue of two ground rods.... (this was found in another thread here in the forum)
The water bond does not have to be bare, FYI.
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Old 10-24-2008, 10:35 PM   #14
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Ok, lots of answers about the ground wire. To be safe, I will get a bare copper wire. The ground from my main panel is bare, so I will just maintain consistency. However, when I built an addition on my house, the elecrtical code official had me drive a secondary ground rod within 8' feet from the first. He did not mention that the ground wire path couldn't be broken. I just clamped a piece from the first rod to the second rod. He didn't make me replace the wire with a continuios piece. Thanks for all the input. I just finished running all of the wire through the conduit and filled in the trench. I was working with flood lights. I hope my neighbor didn't think I was burying my wife!
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Old 10-24-2008, 10:36 PM   #15
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By code the ground wire can be green or bare . Taped #6 is technically not allowed , if you want to nit-pick . Bare wire through a metal raceway has to be bonded on both ends ,but with PVC it doesn't matter . You are probably right about the 25 ohms thing , but here in Louisiana , it is not an issue .
I do love to nit pick! So, any ground wire has to be bonded to the ends of the conduit, not just bare. Green ones too. When you connect the EGC to the box at both ends, then you've accomplished this.

But, Equipment Grounding Conductors aren't the same as Grounding Electrode Conductors. GEC's do not have to be any specific color. Sure it's nice to see that it's green, but it can also be black or bare or whatever.

As far as the 25 ohms. It is likely in the code in your area, but it's not a subject the inspectors have bothered to enforce. It was only about 5 years ago that cities and counties around Atlanta started to pay it any attention. Several counties in North Georgia, last time I checked, still didn't. In fact, it was required in the oldest code I have every put my eyes on: 1915 or thereabouts.

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