GEC sizes

[Grouch1980]

Hi all,
Let's say I have multiple grounding electrode conductor taps, originating from several service switches. All GEC taps terminate in a grounding bus bar. Then, from the grounding bus bar I have one GEC going to the cold water pipe, another GEC going to a ground rod, and a 3rd GEC going to building steel,

1. Can the GEC to the pipe be only a #6 AWG? Since after the pipe, the GEC doesn't extend further, I'm assuming that #6 is all that is needed, as opposed to fully sized.
2. Can the GEC to the ground rod also be sized for #6 AWG? For the same reason, since it doesn't extend further.
3. And the GEC to building steel would be fully sized, based on the size of the largest service entrance conductor.

Thanks for the help.

 

[Dennis Alwon]

The size of the grounding electrode conductor depends on the service conductor sizes T.250.66 so we can't tell if the #6 is correct.

The ground rod never has to be larger than #6. The water pipe and steel would be #4 if you have a standard 200 amp service

 

[infinity]

The GEC to a water pipe electrode is sized according to Table 250.66. Maximum size required is #3/0.

 

[Grouch1980]

So when do you apply 250.66(A)? It mentions where the GEC doesn't extend to other types of electrodes, #6 is the largest that is needed. That's where I got the size for 1 and 2 above. Or does this section not apply when you have GEC taps?

 

[augie47]

250.66(A) references rod and "pipe" but that does not refer to water pipe grounding electrode.
Metal water piping as an electrode or not must be bonded per 250.104.

 

[Grouch1980]

why is it located at 250.104? this whole article 250 zig zags everywhere way too much.

So it's full size to the cold water pipe then at all times. What about to the ground rod? can I use a #6 based on 250.66(A) or does that have to be full size based on my example in Post #1?

 

[infinity]

Ground rod max required #6, water pipe electrode max required #3/0, CEE max required #4.

 

[Dennis Alwon]

why is it located at 250.104? this whole article 250 zig zags everywhere way too much.

So it's full size to the cold water pipe then at all times. What about to the ground rod? can I use a #6 based on 250.66(A) or does that have to be full size based on my example in Post #1?

Read the heading on T250.102... that is for bonding and grounded conductors

I already stated the ground rod info. The largest size is #6 to a rod unless you bond thru to other electrodes that may need a larger bond. For instance, if you went to the rod and jumped to the water pipe then the conductor would be sized for the water pipe to the rod. Stand alone the rod only needs #6

 

[don_resqcapt19]

why is it located at 250.104? this whole article 250 zig zags everywhere way too much.

So it's full size to the cold water pipe then at all times. What about to the ground rod? can I use a #6 based on 250.66(A) or does that have to be full size based on my example in Post #1?

The grounding electrode connection to the water pipe is sized per 250.66 and required by 250.50 which sends you to 250.52(A)(10 through (7). The rule in 250.104, is for bonding the interior metal water piping where there is no metal underground water pipe used as a grounding electrode.

 

[augie47]

I can see where it might be confusing in that "water pipe" is not directly addressed in 250.66 as it is not an "except as permitted"in (A) thru (C)",however (A) includes "Pipe" electrodes. You seldom see a driven pipe as an electrode, so it's an understandable mistake.
On the other hand, I have never understood why bonding metal water piping requires a full size 250.66 conductor where other piping does not,.
(That was the reason I mentioned 250.104 earlier)

 

[Grouch1980]

Thanks guys for the feedback. I'll read through this tomorrow, with the 2017 NEC next to me. Just a really busy day today.

 

[don_resqcapt19]

I can see where it might be confusing in that "water pipe" is not directly addressed in 250.66 as it is not an "except as permitted"in (A) thru (C)",however (A) includes "Pipe" electrodes. You seldom see a driven pipe as an electrode, so it's an understandable mistake.
On the other hand, I have never understood why bonding metal water piping requires a full size 250.66 conductor where other piping does not,.
(That was the reason I mentioned 250.104 earlier)

Yes, there is no reason for the bonding connection to interior metal piping to be larger than the EGC for the largest circuit in the building.