250.66 grounding electrode conductor

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M

mhanson

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Location
Redwood City, CA
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General Journeyman Electrician
Good day all.
Our company has recently installed a 400amp 1ph resi. Service.
While on site I noticed a #3 cu GEC had been installed from the service entrance to the UFER Grounding electrode.
I was under the impression this is to be sized per
T 250.66 ( 1/0 cu )
In looking over 250.66 (B) it looks as though we are not required to be larger than #4AWG cu.

Am I reading this correctly?
Thank you
Michael Hanson
 
Yes, the GEC to a CEE is sized according to T250.66 but it is not required to be larger than #4. A #3 is therefore code compliant.
 
infinity said:
Yes, the GEC to a CEE is sized according to T250.66 but it is not required to be larger than #4. A #3 is therefore code compliant.
Click to expand...

This is great news for the project planner.
I'm curious, under what circumstance would one use 1/0 as stated in T250.66?

Additional note: I find it odd that an equipment
grounding cond. as stated in T250.122 is sized larger (#3) than the G.E.C. (#4).
Thanks
Michael H.
 
mhanson said:
This is great news for the project planner.
I'm curious, under what circumstance would one use 1/0 as stated in T250.66?

Additional note: I find it odd that an equipment
grounding cond. as stated in T250.122 is sized larger (#3) than the G.E.C. (#4).
Thanks
Michael H.
Click to expand...
GEC's are not intended to handle system ground fault current.
 
mhanson said:
This is great news for the project planner.
I'm curious, under what circumstance would one use 1/0 as stated in T250.66?

Additional note: I find it odd that an equipment
grounding cond. as stated in T250.122 is sized larger (#3) than the G.E.C. (#4).
Thanks
Michael H.
Click to expand...
The #4 is an exception to Table 250.66 for ufer grounding electrodes. There is an exception for ground rods, #6 is all that's required for them.

Water bonds, building steel all have to be full size.
 
ActionDave said:
The #4 is an exception to Table 250.66 for ufer grounding electrodes. There is an exception for ground rods, #6 is all that's required for them.

Water bonds, building steel all have to be full size.
Click to expand...

I can imagine a ground rod has greater resistance than the the UFER. I'm obviously not clear on these exceptions.
So in my case, the GEC is installed from the service equipment to the UFER and then continues unspliced to the water main.
And as I understand, this is OK to be installed with
#3 CU.?

And in cases where I have only a ground rod, I need only install a #6 as long as the installation is not subject to physical damage.?

Thanks again for all the great comments
Michael H.
 
mhanson said:
I can imagine a ground rod has greater resistance than the the UFER. I'm obviously not clear on these exceptions.
So in my case, the GEC is installed from the service equipment to the UFER and then continues unspliced to the water main.
And as I understand, this is OK to be installed with
#3 CU.?

And in cases where I have only a ground rod, I need only install a #6 as long as the installation is not subject to physical damage.?

Thanks again for all the great comments
Michael H.
Click to expand...
The key determinant in these cases is whether the GEC or jumper is a "sole" connection. Where continued or jumped to additional [different] electrodes, it is not the "sole" connection and must be sized per the Table.
 
mhanson said:
This is great news for the project planner.
I'm curious, under what circumstance would one use 1/0 as stated in T250.66?

Additional note: I find it odd that an equipment
grounding cond. as stated in T250.122 is sized larger (#3) than the G.E.C. (#4).
Thanks
Michael H.
Click to expand...

As noted GEC and EGC are not there for same purposes.

You will find that for most typical 200 amp services you will need a 4 AWG GEC, but only need a 6 AWG EGC for a 200 amp feeder or branch circuit, larger conductor is the GEC in that case.
 
mhanson said:
This is great news for the project planner.
I'm curious, under what circumstance would one use 1/0 as stated in T250.66?

Additional note: I find it odd that an equipment
grounding cond. as stated in T250.122 is sized larger (#3) than the G.E.C. (#4).
Thanks
Michael H.
Click to expand...

If you have a 400 amp service and there are no service conductors involved then 1/0 is required. An example of this would be a 400 amp meter/ main combo unit.

If you install a 400 amp meter base and use 2- 200 amp panels with say 3/0 copper as service conductors then the grounding electrode conductor only needs to be sized to 2 copper. This is coming from the notes 1 &2 from 250.66

Also as Smart stated-- you cannot run a #4 to the concrete encased electrode and then go on to the water pipes or other electrodes which require a larger conductor. The #4 can go directly to the concrete encased electrode but not any further in this case. Same is true for the ground rod using #6. The water pipes will need to be connected back to the service with a conductor rated for the service based on 250.66 either thru the other electrodes or separately.

If you have a concrete encased electrode then there is no need for a ground rod.
 
Smart $ said:
The key determinant in these cases is whether the GEC or jumper is a "sole" connection. Where continued or jumped to additional [different] electrodes, it is not the "sole" connection and must be sized per the Table.
Click to expand...

Ok, so I must remove my #3 connection from the UFER to the water main and replace this short section with 1/0cu. Or do I simply not need to use the water main at all?

Michael h.
 
If the water pipe qualifies as an electrode then you must use it. You need the #1/0 to go from the service neutral to the water pipe, if you so choose you can hit the CEE along the way.
 
You can also leave the #3 (which could have been #4) between the water and the CEE, but you need the full sized GEC from service to the water.
 
Smart $ said:
The key determinant in these cases is whether the GEC or jumper is a "sole" connection. Where continued or jumped to additional [different] electrodes, it is not the "sole" connection and must be sized per the Table.
Click to expand...

Smart $ - I've read thru several documents in an attempt to understand the wording of 250.66 (C). This section is not stated as "sole" connection, but rather "that portion of the conductor that is the sole connection".
to me I understand this to be that portion of the conductor making a connection from the Service entrance equipment and the UFER shall not be required to be larger than a #4 AWG CU, and that portion of this same conductor that extends from the UFER to the Water Main where it enters the house, will be considered a "Bonding Jumper" (250.53 (C) ) and is to be sized also using the same set of rules in 250.66 including the exceptions (A), (B), and (C)

so the way I'm reading this, in my case the #3CU conductor installed from the Meter to the UFER and continuing to the water main is acceptable.

Please help to clarify if I am misunderstanding something.

Thank You once again for all of your assistance and experience.

Michael Hanson
 
mhanson said:
...so the way I'm reading this, in my case the #3CU conductor installed from the Meter to the UFER and continuing to the water main is acceptable.
Click to expand...
You have to run a 1/0 GEC from meter to water pipe. You can connect to the CEE along the way.
 
mhanson said:
250.66 (A) connections to pipe not required to be larger than#6cu.
Click to expand...

I think you are looking at the requirements for a "pipe electrode" as described in 250.52(A)(5).
That kind of pipe electrode refers to a dedicated driven pipe only. The water pipe electrode is actually described in 250.52(A)(1) instead and is not subject to the #6 Cu limitation.

What Jumper said! (crossing posts)
 
luckylerado said:
In cases where you install only a single ground rod you must have a resistance to earth of 25Ω or less or provide supplemental electrode.
Click to expand...


We have 2 inspectors in Charlotte County Fl that allow one ground rod and a water ground and insist that they are correct. I use two everywhere in case I forget what county I'm working in.
 
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