# Brain tease: Grounding and Bonding



## jar546 (Jan 4, 2011)

On a residential structure if you have a 200A overhead service with 4/0-4/0-2/0 Al SE cable, what is the minimum size conductors you can use for:

1) Connection to ground rods

2) Connection to a water pipe

3) Connection to a concrete encased electrode


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## chris kennedy (Jan 5, 2011)

1) Sole connection? #6cu. (250.66(A))

2) #4cu (T250.66)

3) #4cu (250.66(B))


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## peach (Jan 5, 2011)

#6, #4, #4... (copper of course) and I didn't need Chris' response first..


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## jar546 (Jan 5, 2011)

OK, no argument there but what if it were a 100A service with 2/2/4 SE cable?

1) Ground Rods

2) H2O pipe

3) CEE


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## peach (Jan 5, 2011)

even if you have a 2000 amp service, all the NEC requires is a #6 for a ground rod.  250.66(A) & .52 .. if the underwater H2O pipe qualifies at a grounding electrode, it looks like #6... CEE.. #4.


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## jar546 (Jan 5, 2011)

Are you sure the CEE would require a #4 for a 100A service?


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## Francis Vineyard (Jan 5, 2011)

Gotcha; "shall not be required to be larger than 4 AWG copper conductor"


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## peach (Jan 5, 2011)

go to IRC 3608.1.2 .. "bare copper conductor not smaller than 4 AWG...


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## Francis Vineyard (Jan 5, 2011)

peach said:
			
		

> go to IRC 3608.1.2 .. "bare copper conductor not smaller than 4 AWG...


Let's not confuse electrodes with grounding conductors; Table E3603.1 fn d

But I think it would be wise in use #4 cu


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## jar546 (Jan 5, 2011)

NEC 250.66(B) says:

(B) Connections to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.

The size is however in accordance with Table 250.66

The actual size of a concrete encased electrode would be a 1/2" rebar or a minumum 4awg copper

Do we arrive at the same conclusion for a 100A service if with use the NEC or the IRC?  riddle me that


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## jar546 (Jan 5, 2011)

Come on folks, little participation.

OK, so on my 100A service I want to run a #8cu to my water pipe and ground rods.  Can I?


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## raider1 (Jan 5, 2011)

jar546 said:
			
		

> Come on folks, little participation.OK, so on my 100A service I want to run a #8cu to my water pipe and ground rods.  Can I?


Yes, but the #8 would have to be installed in RMC, IMC, Schedule 80 PVC, EMT, or a cable armor.

(See 250.64(B))

Chris


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## jar546 (Jan 5, 2011)

Thanks Chris you party pooper.

My point in this exercise was that as inspectors, we always see #6 for 100A services, not because that is the minimum size but because it is the most economical size to install since you don't have to protect it.  If someone saw this for the first time, they may fail it because we rarely if ever see anyone use the #8 because of the protection requirement.


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## raider1 (Jan 5, 2011)

jar546 said:
			
		

> Thanks Chris you party pooper.


Sorry  



> My point in this exercise was that as inspectors, we always see #6 for 100A services, not because that is the minimum size but because it is the most economical size to install since you don't have to protect it.  If someone saw this for the first time, they may fail it because we rarely if ever see anyone use the #8 because of the protection requirement.


I agree.

Chris


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## Francis Vineyard (Jan 5, 2011)

jar546 said:
			
		

> Come on folks, little participation.OK, so on my 100A service I want to run a #8cu to my water pipe and ground rods. Can I?


And a #8 cu to the Ufer!

Here's one I see often; 4/0-4/0-2/0 Al SE cable; two 200 amp main disconnects with a single #6 grounding electrode conductor routed from one panelboard through the other unspliced to the ground rods.

What's the violation?

Jeff I hope you don’t mind. UB I could use some pop quizzes in plumbing.


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## TimNY (Jan 6, 2011)

Very informative, thanks jar et al.


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## raider1 (Jan 6, 2011)

Francis Vineyard said:
			
		

> And a #8 cu to the Ufer!


Correct, you can run a #8 to the UFER provided that it is protected.



> Here's one I see often; 4/0-4/0-2/0 Al SE cable; two 200 amp main disconnects with a single #6 grounding electrode conductor routed from one panelboard through the other unspliced to the ground rods.What's the violation?


How is the GEC connected to the 2 panels?

Chris


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## Francis Vineyard (Jan 12, 2011)

raider1 said:
			
		

> How is the GEC connected to the 2 panels? Chris


 Sorry for the delay; been running around like a cat in a room full of rocking chairs!  It's a shame to see this time and time again.
	

		
			
		

		
	

View attachment 334


View attachment 334


/monthly_2011_01/572953bcd01f8_2MainPB.jpg.6d348c67a34e2e86bef936b7d96c1095.jpg


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## jar546 (Jan 12, 2011)

There is nothing wrong with that grounding electrode system.  I don't like it, would not do it that way but it is code compliant.  I actually called the NFPA about this situation last year and yeah, not a problem


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## north star (Jan 12, 2011)

** * * **

Francis & jar,

I believe that Art. 250.130(A) allows it, as long as it is properly attached to the

grounding terminal, in each panelboard.

** * * **


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## Francis Vineyard (Jan 12, 2011)

I think this is not a sole conductor but a common conductor;



depending on the choices and edition chosen; 2008 250.64 D or 2006 250.64 (D) & (F)



and the primary water pipe electrode is not correct sized to Table 250.66 with the SE of 500 kcm



FYI the POCO won’t let us use grounding conductors in there equipment.


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## raider1 (Jan 13, 2011)

north star said:
			
		

> ** * * **Francis & jar,
> 
> I believe that Art. 250.130(A) allows it, as long as it is properly attached to the
> 
> ...


250.130 is dealing with equipment grounding and does not apply to the grounding electrode system.

Chris


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## raider1 (Jan 13, 2011)

Francis Vineyard said:
			
		

> I think this is not a sole conductor but a common conductor;


I agree, the conductor connecting the 2 panels is not the sole connection to the ground rods and therefore can't be size to the #6.



> depending on the choices and edition chosen; 2008 250.64 D or 2006 250.64 (D) & (F)
> 
> 
> 
> ...


The problem that I see with this set up is it does not follow one of the methods listed in 250.64(D)

The water pipe and the ground rods connect at different enclosures and do not connect to a single GEC as specified in 250.64(D)(1) and each electrode would need to be connect to each disconnecting means to comply with 250.64(D)(2) and they don't comply with 250.64(D)(3).

For this to comply with 250.64(D)(1) a single GEC should be run to the water pipe electrode then a bonding jumper run to the ground rods. The single GEC should be sized 1/0 based on the 500 Kcmil service entrance conductors and Table 250.66. Each service disconnecting means could then have a tap run to connect the GEC to the disconnect enclosure and the taps could be sized based on the service entrance conductors supplying each disconnect.

The easiest way to comply with 250.64(D) would be to connect the GEC for the water pipe and for the ground rods to the grounded conductor in the wireway above the disconnecting means in accordance with 250.64(D)(3). The GEC run to the ground rods would only need to be a #6 and the GEC run to the water pipe would have to be a 1/0 in accordance with Table 250.66.

Hope this makes sense.

Chris


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## north star (Jan 13, 2011)

** * * **



> 250.130 is dealing with equipment grounding and does not apply to the grounding electrode system.


Chris, I stand corrected sir!......You are correct!** * * **


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