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Old 05-07-2011, 05:14 PM   #1
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Ground Location and Wire Size


New member; first post. Thanks in advance for reading and responding.

Although Iíve read many posts here related to this subject, Iím still confused.

I have a rural property with 200A meter loop on pole. This includes Milbank socket and 200A Siemens load center (W0816B1200CT) w/ 200A main disconnect and feed-through lugs. Of course the neutral and ground are bonded together there and connected to driven ground rod.

Hereís where my confusion beginsÖ I was told by one electrician that from the main to sub-panel(s), I could run triplex URD cable, and then at the sub-panel I could drive another ground and split the neutral and ground there. In other words, I didnít need to run a separate ground wire from the main to the sub-panel. Several posts here (and a guy at the big box) however, seem to indicate that a separate ground must be run from the main to any sub-panel in addition to the phase conductors and neutral. Which is correct?

If I need to run a separate ground, then what AWG? I will be running to 2 separate sub-panels; one using 4/0-4/0-4/0 via the feed-through lugs and another using 1/0-1/0-1/0 via a 100A breaker in the main (or maybe a 2-pole lug kit). I assume the size of the ground wire is proportional to the conductor size, so what size for each run? Also, if Iím running a separate ground, do I need to drive another ground rod at each sub-panel or is the ground back at the main sufficient for everything? What about plumbing or gas lines? Can they just be grounded through the sub-panel back to the ground at the main? Would separate ground wires need to be sheathed or bare? Iíll be burying the cable in 2Ē or 2.5Ē PVC.
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Old 05-07-2011, 05:37 PM   #2
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Ground Location and Wire Size


the code exception that allowed the 3 wire system has been removed. You are now required to run 4 wires no matter what. You may still need a ground rod at the outbuilding.
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Old 05-07-2011, 05:39 PM   #3
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Ground Location and Wire Size


size of EGC is proportional to the feeder size. all thing in the out building must be bonded, but only to the sub ground bar.
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Old 05-07-2011, 05:45 PM   #4
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Ground Location and Wire Size


sch 40pvc is fine for underground, but your uprisers will need to be sch80. 4-1/0s and ground will fit fine in 2"pvc. And 4-4/0 and ground will fit in 2 1/2" pvc,but you might find it hard to pull and worth going to a larger pipe.


Equipment Grounding Conductors- are sized by table 250.122.
200a-#6
100a-#8

Can somebody confirm that I'm using the right table.
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Old 05-08-2011, 07:55 AM   #5
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Ground Location and Wire Size


Quote:
Originally Posted by Saturday Cowboy View Post
Equipment Grounding Conductors- are sized by table 250.122.
200a-#6
100a-#8

Can somebody confirm that I'm using the right table.
For EGC's, yes you are.
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Old 05-08-2011, 12:29 PM   #6
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Ground Location and Wire Size


Thanks.

Regarding the ground size, is that for copper? I plan to run Al URD for the phase conductors and neutral. Can I run a copper ground in the same conduit or should I use Al for the ground as well? Isn't there some sort of chemical reaction between Cu and Al? I know the URD is sheathed, but over time is it an issue having unlike metals? If I use an Al ground wire, does it become 200A = #4 and 100A = #6? Does the ground need to be sheathed or can it be bare?

You indicated that I may still need a ground rod at the sub-panel location. What would the determining factor be for that?
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Old 05-08-2011, 12:48 PM   #7
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Ground Location and Wire Size


A ground rod is required at the subpanel
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Old 05-08-2011, 09:08 PM   #8
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Ground Location and Wire Size


Quote:
Originally Posted by LHB_Texas View Post
Thanks.

Regarding the ground size, is that for copper?
Yes it was. 100A= #8 Cu or #6 Al, 200A= #6 Cu or #4 Al

Quote:
Originally Posted by LHB_Texas View Post
I plan to run Al URD for the phase conductors and neutral. Can I run a copper ground in the same conduit or should I use Al for the ground as well?
Either. But Al is cheaper.

Quote:
Originally Posted by LHB_Texas View Post
Isn't there some sort of chemical reaction between Cu and Al? I know the URD is sheathed, but over time is it an issue having unlike metals?
The chemical reaction comes when the two metal are in direct contact with each other. There is no direct metal connection between a bare copper wire laying on top of an insulated aluminum wire (or vice versa).

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If I use an Al ground wire, does it become 200A = #4 and 100A = #6?
See above.

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Originally Posted by LHB_Texas View Post
Does the ground need to be sheathed or can it be bare?
In conduit, copper or aluminum can be bare or insulated, though insulated is less likely to damage the other conductors during the pull if all 4 don't move as a group. It can act like a saw in the worst case scenario. Not always likely, but possible. In direct burial, either is allowed if insulated, bare copper is allowed, but bare aluminum is not. Bare aluminum cannot be in direct contact with masonry or the earth or where subject to corrosive conditions, and cannot be terminated within 18' of the earth. Personally, I'd just stay with aluminum...cost issues.

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You indicated that I may still need a ground rod at the sub-panel location. What would the determining factor be for that?
In general, if the sub-panel (feeder panel) is not in the same, attached building as the main service disconnect, it needs a ground rod(s).
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Last edited by SD515; 05-08-2011 at 09:10 PM.
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Old 05-21-2011, 08:47 AM   #9
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Ground Location and Wire Size


I now understand that I need to run a separate ground wire from the main to the sub-panel. I have installed a separate ground bar in the subpanel and driven another ground rod. I will tie the ground bar to the ground rod and any loads will also be tied to the ground bar.

My question is about the ground coming into the subpanel from the main. Since it's bonded to the neutral at the main, do I connect it to the neutral bus at the subpanel, or do I split at that point and attach it to the separate ground bar?

Thanks.
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Old 05-21-2011, 09:12 AM   #10
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Ground Location and Wire Size


The ground wire from the main terminates on the ground bar in the sub-panel. Do not install any bonding strap or screw from the neutral bar to the sub-panel enclosure, or remove them if they are installed already. In the sub-panel, the neutrals and the grounds will be isolated from each other. Only in the service disconnect (the equipment that houses the first breaker after the meter) are the neutral and the grounding wires connected.
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Old 05-23-2011, 01:11 PM   #11
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Ground Location and Wire Size


Thanks again. Seems like every time I get an answer, I think of more questions.

Regarding connecting phase conductors in the sub-panel. I will be running from a 100A double pole breaker in the main to a 100A main lug subpanel using 1/0-1/0-1/0 triplex cable. The neutral has a yellow stripe, so no problem identifying it and connecting properly at the subpanel. The two phase conductors are both black. Do I need to be concerned about which phase conductor is connected to which lug in the subpanel? For instance does the conductor connected to the left lug in the main panel have to be connected to the left lug in the subpanel or could they be connected on opposite lugs. There will be one 240V load at the subpanel (well pump). If they have to be connected the same, how do I tell which is which when both conductors are black? Remember that this is a triplex cable rather than separate conductors, so it's going to be hard to visually trace an individual conductor from end to end.

Thanks again.
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Old 05-23-2011, 01:27 PM   #12
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Ground Location and Wire Size


you also need a ground conductor.4 wires total.as for identifing,with no power on,tie neutral to a black wire,go to other end and look for continuity between one of the black wires and neutral wire.put some red tape on black wire at both ends.if wire is just coiled up and not installed it would be eaiser.
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Old 05-23-2011, 01:29 PM   #13
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Ground Location and Wire Size


Quote:
Originally Posted by NJMarine View Post
A ground rod is required at the subpanel
Can you quote the NEC location where it requires a ground rod at a sub panel. Please quote the NEC location you are using.
I don't believe you are correct.

Last edited by wareagle; 05-23-2011 at 01:44 PM.
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Old 05-23-2011, 02:02 PM   #14
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Ground Location and Wire Size


Quote:
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Can you quote the NEC location where it requires a ground rod at a sub panel. Please quote the NEC location you are using.
I don't believe you are correct.
We are believe the OP is installing the sub-panel in a building separate from the service disconnect, as his serv discon is on a pole. 250.32
Of course, additional grnd rods aren't required if the feeder panel is in/on the same structure the main discon is.
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Old 05-23-2011, 02:15 PM   #15
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Ground Location and Wire Size


Quote:
Originally Posted by LHB_Texas View Post
Thanks again. Seems like every time I get an answer, I think of more questions.

Regarding connecting phase conductors in the sub-panel. I will be running from a 100A double pole breaker in the main to a 100A main lug subpanel using 1/0-1/0-1/0 triplex cable. The neutral has a yellow stripe, so no problem identifying it and connecting properly at the subpanel. The two phase conductors are both black. Do I need to be concerned about which phase conductor is connected to which lug in the subpanel? For instance does the conductor connected to the left lug in the main panel have to be connected to the left lug in the subpanel or could they be connected on opposite lugs. There will be one 240V load at the subpanel (well pump). If they have to be connected the same, how do I tell which is which when both conductors are black? Remember that this is a triplex cable rather than separate conductors, so it's going to be hard to visually trace an individual conductor from end to end.

Thanks again.
On a single phase system, no you don’t need to know which ‘hot phase’ is connected to which main lug in the sub-panel.

You mentioned you’re using a main-lug panel? You know that if this panel is in a separate building, it also requires a disconnect? You should be able to get a 100A breaker and a hold down kit for that panel. You would attach your 1/0 to the breaker and not to the lugs (backfeed the breaker).
You are running a ground wire too, right?
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