Grounding rod conductor dimensions for 200amp service

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Old 11-30-14, 10:20 AM
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Grounding rod conductor dimensions for 200amp service

Hi,

I'm trying to understand Section 250.66 of the NEC 2014 (National Electrical Code) document for how to connect the ground of an electrical service to the electrode system.

So basically it says in Table 250.66 if I'm using 4/0 Aluminum wire to supply my 200Amp service and there is is a feeder between the Service Disconnect and the Breaker Panel that is 20 feet away (i'm using my case for an example), then the ground conductor in that bundle needs to be AWG #2 size (aluminum).

If I'm connecting the Service Disconnect panel ground bus to a grounding electrode system (ground rod or grounded metal water main), then that conductor never has to be thicker than AWG #6 Copper per 250.66.A.

Am I understanding this right?
 

Last edited by zootjeff; 11-30-14 at 10:21 AM. Reason: typo
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Old 11-30-14, 10:41 AM
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Your Grounding electrode will be #6 copper. You will ground the breaker panel as well as the disconnect to the grounding rod system.
 
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Old 11-30-14, 11:48 AM
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If I'm connecting the Service Disconnect panel ground bus to a grounding electrode system (ground rod or grounded metal water main), then that conductor never has to be thicker than AWG #6 Copper per 250.66.A.
#6 copper to the ground rod and #4 copper OR #2 aluminum to the water service.
 
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Old 11-30-14, 12:03 PM
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As others have mentioned, conductor to ground rod never is required to be larger than #6 copper.
 
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Old 11-30-14, 12:08 PM
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If you are using something like SER cable between panels the grounding conductor should be the correct size.
 
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Old 11-30-14, 02:09 PM
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Name:  200A Service Diagram.jpg
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Size:  40.8 KB

Here is what I'm proposing. Do I need a separate ground connection to the Breaker Panel (which would create a ground loop) or is the ground in the wire bundle sufficient for grounding the Breaker Panel?
 
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Old 11-30-14, 02:25 PM
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You need the 4 wire feeder, but there will not be a ground rod at the second panel.
 

Last edited by pcboss; 11-30-14 at 02:51 PM.
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Old 11-30-14, 02:39 PM
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You might need two ground rods at your meter/main depending on your local requirements as this is your main service.

The ground wire should go to one of the ground bars in the 200 amp panel, not to the neutral bar, since they are available. I never recommend removing the factory strap because it will cut your neutral holes in half.

While you do not need a ground rod at the 200 amp panel, you can add one if you want, I would still bond your water service to the house panels ground bar.

Check to make sure you are wiring to the LINE side of the meter, which in most cases is on the top of the meter. Also, check that the meter/main panel is approved by your local power company.
 
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Old 11-30-14, 02:47 PM
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Is this the SER wire you are talking about between the Meter Main and the Breaker Panel?

http://platt.com/pl/4A3SERGX500

This is (3 insulated) 4/0 and (1 bare stranded) 2/0.

Am I correct in interpreting the NEC in that I only need #2 AWG for the ground, but they don't really make a SER cable with 4/0 and #2 Aluminum so I just get the 4/0-4/0-4/0-2/0 bundle?

-Jeff
 
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Old 11-30-14, 02:56 PM
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The ground wire should go to one of the ground bars in the 200 amp panel, not to the neutral bar, since they are available. I never recommend removing the factory strap because it will cut your neutral holes in half.
So you are saying I should use both isolated bus bars (over the black plastic) for Neutral, and not bond either of them to the panel, and have the stranded ground cable from the SER cable attach to the bus bars on either side (mounted directly on the metal of the enclosure) that are otherwise unused? I don't really terminate into a hex lug on the ground wire, but take a few strand bundles and go to the side bus-bars..

There are ~30 connections for each isolated bus bar, so I either do this, or I double up in some of them if I fill the panel to 40 circuits.. Since I will likely have quite a few ganged breakers, It's unlikely I'll use all 40 of them for neutral and ground connections..

Seems like that makes a lot of sense because the Romex would have to route all the way around the breaker section if I try to do it like I've drawn... I'll update the drawing..
 
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Old 11-30-14, 03:13 PM
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Here is the updated drawing with dual ground rods, and optimal ground bus-bar usage for the breaker panel
Name:  200A Service Diagram v2.jpg
Views: 31474
Size:  39.0 KB

The 50kB image limit sucks, here is a close-up:

Name:  200A Service Diagram v2 detail.jpg
Views: 20668
Size:  38.5 KB
 
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Old 11-30-14, 03:14 PM
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The bars shown may both be neutral bars. What brand panel are you using?
 
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Old 11-30-14, 03:19 PM
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Breaker Panel: Siemens-P4040B1200CU
Meter Main:Siemens-MC0816B1200ESN
 
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Old 11-30-14, 03:53 PM
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Looks good. Use this for connecting the #2 AL to the ground bar:

[ATTACH=CONFIG]42556[/ATTACH]
 
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Old 11-30-14, 03:59 PM
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Use this for connecting the #2 AL to the ground bar:
So is it #2 AWG or is it 2/0? I can't seem to find SER cable that has 4/0-4/0-4/0-#2. It looks like it is all 4/0-4/0-4/0-2/0. Is that right?

Table 250.66 of the 2014 NEC seems to indicate that I need #2 AWG, but doesn't look like they make it.. Am I missing something? Do you just split it into a few sets of strands, or do you just cut off the excess to an equivalent #2 out of the 2/0?
 
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Old 11-30-14, 04:04 PM
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I doubt you will find more than one version of 4/0 SER..
 
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Old 11-30-14, 04:07 PM
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Table 250.122 shows you only need #4 aluminum for 200 amp. You can go larger if that is all you can find. 2/0 is fine.
 
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Old 11-30-14, 04:09 PM
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Do you just split it into a few sets of strands, or do you just cut off the excess to an equivalent #2 out of the 2/0?
Neither is an approved method. You use the corect size of the adapter shown in post #14.

Examples: http://www.homedepot.com/catalog/pdf...cfe1ab0987.pdf
 
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