Ground to water main

[brother]

I say #2 is all you need. Note 1 T. 250.66. Table 8 has 3/0 at 167800 cir mil. Multiply by 2 and you get 335600 cir mil. This is equi. to 350 KCM. Table 250.66 allows #2 for 350 KCM copper

I was comming up with something different, 167800 cir mil 3/0 Multipied by FOUR 4 instead 2 that would be 167800 * 4 = 671200 which means a 2/0 copper GEC according to table 250.66.

The reason I see 4 instead of 2 3/0 is he said he had 2 200 amp breakers (Homeline), Im assuming that there are 2 3/0 to EACH breaker (correct me if im wrong), which would give you a total of 4 3/0 wires.

The GEC is sized according to the total circular mills of the ungrounded conductors 2008 NEC 250.24(D), 250.30(A)(3), AND of course 250.66.

By the way is the a single phase service (residential)??

 

[Dennis Alwon]

I was comming up with something different, 167800 cir mil 3/0 Multipied by FOUR 4 instead 2 that would be 167800 * 4 = 671200 which means a 2/0 copper GEC according to table 250.66.

The reason I see 4 instead of 2 3/0 is he said he had 2 200 amp breakers (Homeline), Im assuming that there are 2 3/0 to EACH breaker (correct me if im wrong), which would give you a total of 4 3/0 wires.

The GEC is sized according to the total circular mills of the ungrounded conductors 2008 NEC 250.24(D), 250.30(A)(3), AND of course 250.66.

By the way is the a single phase service (residential)??

They are talking about the size of the largest service entrance conductor not the size of the sum of both phases. Only 2- 3/0 conductor

 

[M. D.]

I say #2 is all you need. Note 1 T. 250.66. Table 8 has 3/0 at 167800 cir mil. Multiply by 2 and you get 335600 cir mil. This is equi. to 350 KCM. Table 250.66 allows #2 for 350 KCM copper

If the NEC does not cover factory installed wiring can we then use said wiring to determine the size of GEC??? If the answer is yes ,.. then I agree with Dennis

 

[gotmud]

I say #2 is all you need. Note 1 T. 250.66. Table 8 has 3/0 at 167800 cir mil. Multiply by 2 and you get 335600 cir mil. This is equi. to 350 KCM. Table 250.66 allows #2 for 350 KCM copper

This is how I see it and this is how WE do it around here....

 

[Dennis Alwon]

If the NEC does not cover factory installed wiring can we then use said wiring to determine the size of GEC??? If the answer is yes ,.. then I agree with Dennis

Well I see it this way if we use the factory installed buss to determine the gec then why not the factory installed 3/0's. It only makes sense and the NEC doesn't care who installs it. They may not have a say on the factory equipment but if it is there then I don't see why we can't use it.

I agree the buss needs 1/0 but not the parallel 3/0 and I am sticking to my guns.:grin: To me it would be ludicrous to allow a #2 EGC if the EC installs 3/0 but if the factory installs them a 1/0 would be needed.

 

[brother]

They are talking about the size of the largest service entrance conductor not the size of the sum of both phases. Only 2- 3/0 conductor

its my understanding that its the SUM of phases. Looking at the Nec 2008 handbook, they give an example of 2 services , one has an ungrounded conductor of # 1 for the service and the other has a #4 if recall correctly, when they are joined to the same GEC you have to add both of them to get the correct size gec.

Since the 2 3/0 are going to the same enclosure and they parralled to get the amout of current needed, it just seems like you would add them all because of the available potential current. At least thats how I read the notes on the table of 250.66. Only time you dont have to go bigger is when its connecting to the rod, or concrete encased electrodes 250.66 (A)(B).

 

[Dennis Alwon]

its my understanding that its the SUM of phases. Looking at the Nec 2008 handbook, they give an example of 2 services , one has an ungrounded conductor of # 1 for the service and the other has a #4 if recall correctly, when they are joined to the same GEC you have to add both of them to get the correct size gec.

Since the 2 3/0 are going to the same enclosure and they parralled to get the amout of current needed, it just seems like you would add them all because of the available potential current. At least thats how I read the notes on the table of 250.66. Only time you dont have to go bigger is when its connecting to the rod, or concrete encased electrodes 250.66 (A)(B).

Brother, I don't know what the handbook states but it seems you are mixing apples with oranges. The case I am citing is a parallel conductors. The one you cite is not but you are correct they must be summed

You would take #1 and the #4 and add their cir mil but you don't add 2-#1's and 2-#4's to get their cir. mil.

 

[Dennis Alwon]

I

The GEC is sized according to the total circular mills of the ungrounded conductors 2008 NEC 250.24(D), 250.30(A)(3), AND of course 250.66.

By the way is the a single phase service (residential)??

So are you telling me that a 200 amp 3 phase system would need a GEC larger than a single phase system? I think not