Sizing GEC for a practice problem

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ivsenroute

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For some reason, I continue to not get the same answer that the practice test that I am taking has. I don't know what I am missing but I don't get the answer at all. What do you come up with in copper?

The minimum size grounding electrode conductor for a 120/240 volt AC service with three sets of 1/0 AWG aluminum conductors is:
 
ivsenroute said:
What do you come up with in copper?
Come iven...you know how we play this game around here....you tell us your answer and how you got there....then we tell you what we got and how....then before you know we are debating if a 3rd SABC is allowed in a dwelling unit kitchen :D

So what did you get?

EDIT:
Are these parallel conductors?
 
I simply went to Table 250.66 and chose 8awg copper

I was not sure if I should figure the cross sectional area and add them all but that did not work either
 
If these are parallel conductors you'll need to add together the circular mil area of the 3 sets of #1/0, then look in 250.66.
 
infinity said:
If these are parallel conductors you'll need to add together the circular mil area of the 3 sets of #1/0, then look in 250.66.

You will find the cir. mil in Table 8 of Chapter 9.
 
infinity said:
If these are parallel conductors you'll need to add together the circular mil area of the 3 sets of #1/0, then look in 250.66.

I tried that too but it did not work out either. When I did that the circular mills added up to 633,600 which give you an answer of 1/0 copper which is also not a correct answer.


If you reduce the 633,600 by 61% per Note 4 at the bottom of Table 8 then you can get the answer. Problem is that the aluminum is larger than copper so a reduction is the exact opposite as you would expect.
 
No you know the answer which is not what I wanted to happen, I wanted everyone to try it on their own to see what they got. Instead I was given directions which I already knew and tried. No one attempted to figure it out on their own.

I think this may be a problem with the problem............ ;)
 
1/0 =105600

Multiply by 3

105600 X 3= 316800

That is equivalent to a 350 MCM since the cir mil is greater than 300MCM

T. 250.66 says #2 copper

You multiplied by 6 not 3
 
ivsenroute said:
Why 3 and not 6? There are 3 sets which means 6 ungrounded conductors.

Yes, but you are looking for the largest phase conductor. T. 250.66- size of largest ungrounded SE conductor. You are also dealing with Note 1
 
So whether it was 3ph with 3 ungrounded conductors or single phase 120/240 with two we would consider that 1 set and only count per "set" such as SE cable.

Thanks for the clarification, I appreciate it and now understand it. Note 4 does not come into play then I assume
 
ivsenroute said:
So whether it was 3ph with 3 ungrounded conductors or single phase 120/240 with two we would consider that 1 set and only count per "set" such as SE cable.

Thanks for the clarification, I appreciate it and now understand it. Note 4 does not come into play then I assume
YW and 3 phase makes no difference.

There is no Note 4. Note 2 does not come into play unless you have no se conductors. An example would be a self contained meter panel combo where there is a buss bar but no conductors.
 
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