New cell tower service

[rawlands]

I am installing a new 800a meter bank for a new cell tower site. There will be 4 200a meter/disconnects and no main. 120/240v 1phase. We will be using pvc under ground. How does 2-3" with 2 sets each of 300 aluminum sound. Am I safe in figuring I will not get 90c lugs in the service gear? Also, as far as the grounding electrode goes, Will a ground rod, and the grounding loop around the tower (spec to be 5ohms or less and #2 tinned copper) be sufficiant?

 

[Sparky Joe]

When I did cell sites for NexTel the sites ground ring was never tied into the service only to the tower and anteanna cables. We used a ground rod and a ufer though I notice other sites don't have the elaborate shelter that NexTel sites do so I don't know if a ufer is available.
Size your pipe and wire according to the NEC, of course. And I've never in any installation sized wire to the 90 degree column, I still have yet to see a lug rated for 90 degrees.
It seems your specs are pretty explicit, isn't any of this stuff listed?

 

[rawlands]

No, nothing is listed for the service. The plans are very detailed for the cingular shelter to be added though. You are correct in saying the tower ring should be part of the grounding electrode system, but try to convince some inspectors that. We have been doing a build out for cingular in Minnesota,Wisconsin,and Illinois, and yes they do have a ground ring and 8-10 ground rods around their shelters, and they do get tied to the service. But, being we are doing just the rawland, there wont be any of this to tie to before inspection of our service. I guess a ground rod alone will satisfy the nec. It is the only electrode available on the site. Im just curious as to the service size. Im sure it is not calculated at 800 amps load, maybe I could fudge in some 250 al. instead.

 

[steve66]

How does 2-3" with 2 sets each of 300 aluminum sound.

Without knowing the actual load, you are just guessing at the size of the service conductors. Anything sized less than 800A is just rolling dice.

Steve

 

[rawlands]

After all said and done, we have to go with the full 800a and cu conductors. 4/0 at75c is 230a. 4x>800 95c is 260 x 4= 1040x80%=832a. 2-2.5" pvc with 6 4/0. Done deal! $5/ft for 4/0 x 12 conductors= $60/lin foot WOW!!

 

[bob]

Quote
"After all said and done, we have to go with the full 800a and cu conductors. 4/0 at75c is 230a. 4x>800 95c is 260 x 4= 1040x80%=832a. 2-2.5" pvc with 6 4/0. Done deal! $5/ft for 4/0 x 12 conductors= $60/lin foot WOW!!"

You can use 2 ckts of 500 kcm if the caculated load is not greater that 760 amps.

 

[rawlands]

Bob, I could do that, but the "engineer" says to plan for a full 800a. I feel, for the same price for the copper, that 4/0 is much easier to pull and terminate, even though there are twice the conductors. PVC is only $1.5/foot for 2 1/2". Good choice? anyone?

 

[Sparky Joe]

500's are always a pain to deal with. And I just pulled 4/0's in a 2 inch today, that being said, you really should go with 2.5 PVC