water GEC for 600 amp service

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Bill Turax

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We are installing a 600 amp residential service with a CT cabinet.
there are (3) 200 amp service disconnects. each disconnect is fed with 2/0 CU and the load side has 4/0 AL.
the issue is with the GEC to the cold water pipe. we installed (3) pieces of #4 CU to the cold water, 1 piece from each disconnect. the inspector says we need (1) piece of 1/0 CU or 3/0 AL.

I understand this comes from 250.66 (3 pieces of 4/0 = 635 KCMIL), the chart says this would be 1/0 CU or 3/0 AL. however we are taking a #4 from each disconnect separately so the largest ungrounded conductor in the disconnect is 4/0 AL and per 250.66 that only needs to be a #4 CU.

when installing a 400 amp residential service with (2) disconnects with 4/0 AL w always use (2) pieces of #4 CU for the water GEC and have never had an issue. why would it be different for the 600 amp service with an additional disconnect and #4 GEC?
 
If you run three separate GEC's one from each service disconnect then it needs to be sized according to the SEC's feeding that disconnect which in this case is #2/0. If you ran a single GEC and tapped to each disconnect then the GEC is sized according to parallel sets.

BTW the #2/0 is too small for 200 amps since it's only a 175 amp conductor and not suitable for 200 amps.
 
The #2/0's are service entrance conductors feeding a 3-200 amp servce disconnects, the conductors need to be 200 amps or greater.
 
Thank you all! I don't think I received a straight answer for the GEC however.
can I indeed run a separate piece of #4 CU from each disconnect to the main water, instead of (1) piece of 1/0 CU or 3/0 AL.

also is my 4/0 AL not good for 200 amps using the 83% rule from 310.15(B)(7)(2)?
 
Bill Turax said:
Thank you all! I don't think I received a straight answer for the GEC however.
can I indeed run a separate piece of #4 CU from each disconnect to the main water, instead of (1) piece of 1/0 CU or 3/0 AL.

also is my 4/0 AL not good for 200 amps using the 83% rule from310.15(B)(7)(2)?
Click to expand...

You cannot use the 83% on a service that is greater than 400 amps (already answered)

Yes, I believe you can run a #4 to each disconnect.

Let's go back to the 4/0 aluminum. 4/0 aluminum is good for 180 amps at 75c and article 240.4(B) allows us to use the next higher breaker so you can have a 200 amp breaker with 4/0 al but the load on each one cannot be larger than 180 amps. Technically you only have a 540 amp service not 600 amps which is normally plenty good.
 
Totally understood now, thank you so much!
Regarding the GEC, is there a specific code section I can reference that allows the (3) pieces of #4 Cu as described above? when I call the inspector I would like to be able to site an exact code section.
 
Bill Turax said:
Thank you all! I don't think I received a straight answer for the GEC however.
can I indeed run a separate piece of #4 CU from each disconnect to the main water, instead of (1) piece of 1/0 CU or 3/0 AL.
Click to expand...

I think that it's in post #2. :) Packer gave you the code reference.
 
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