sizing waterpipe ground

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mjac

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confused about sizing water main ground for 400a underground service with 350mcm to line side of meter and two 2" conduits with 3/0 from the load side of the meter into two 200a panels. can size be found just by looking at 250-66 or because of the parallel conduits is there a different way?
 
You would size it per Table 250-66 to the Service Lateral which would be the 350's.

Roger
 
Tony, it seems to me that Mjac is asking the right questions and just needs some assistance, so why not offer some direction?

Roger
 
It won't make a difference in this example, but 250.66 isn't based on the the size of the service lateral conductors. It is based on the size of the service entrance conductors. If there is no disconnect at the meter, then the two sets of 3/0 conductors from the meter to the panels would be the service entrance conductors. This would be a case where footnote 1 to the table would apply. The sum of the areas of two 3/0 conductors would be 335.6 kcmil. This produces the same answer from table 250.66 as would a 350 kcmil conductor. There could be scenarios where you could get a different result by using the size of the service lateral conductors vs. the size of the service entrance conductors.
 
tonyou812 said:
You gotta do some homework before you come in here kid
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there is always one loudmouth who thinks they know it all on every board. i got your kid right here!
 
roger said:
Tony, it seems to me that Mjac is asking the right questions and just needs some assistance, so why not offer some direction?

Roger
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thanks for the help
 
eprice said:
It won't make a difference in this example, but 250.66 isn't based on the the size of the service lateral conductors. It is based on the size of the service entrance conductors. If there is no disconnect at the meter, then the two sets of 3/0 conductors from the meter to the panels would be the service entrance conductors. This would be a case where footnote 1 to the table would apply. The sum of the areas of two 3/0 conductors would be 335.6 kcmil. This produces the same answer from table 250.66 as would a 350 kcmil conductor. There could be scenarios where you could get a different result by using the size of the service lateral conductors vs. the size of the service entrance conductors.
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thanks for clearing up the confusion
 
Lets look at this another way. Yes you can do your homework and look up the answer in 250.66.
But if you understand that you are sizing the GEC to the water pipe to carry fault current,

And that the fault current is based on the amount that can supplied from the utility source

And that the parallel condutors are actually one conductor, cause they are joined at each end

Knowing that look up the size in table 250.66

Also when sizing the GEC there is a difference between table 250.66 and section 250.66. The section includes rules for where the GEC can be smaller than 250.66

And whey there are those rules is a subject for a different post.
 
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