Grounding at Utility Transformer Poles

[jtester]

I am interested in other views of utility transformer pole grounding. NESC Rule 94B indicates that pole plates and butt wraps are not to be the only grounding electrode at transformer poles.

I rarely see more than a butt wrap on transformer poles around here, particularly in areas served by smaller cooperatives.

What are the practices of other utilities, do they use a ground rod, or is the connection to the system neutral counted as another ground connection?

Thanks

jtester

 

[dpc]

I'm used to seeing ground rods.

David Castor

http://www.cvoes.com

 

[racobb]

I second the ground rods.

Alan

 

[X49]

The local utility here uses three ground rods in a triangular formation. I believe they are arranged to limit step potential for people standing near the pole, and to keep ground resistance low in rural areas where they don't run a neutral.

 

[PHovnanian]

Butt plate plus a ground rod at each pole (not just the transformer locations). Two ground rods may be used for larger (3 phase) banks at the engineer's discretion. But here in Western Washington State, its damp enough that soil resistivity isn't a major issue.

 

[bacon4life]

We use a metal plate that meets the requirements of 94B3c for buried plates, it just happens to be attached to the pole butt. It is several times the size of the pole-butt plate listed in 94B4b.

 

[tinfoil]

We use a 0.2m^2 copper plate electrode (per CSA 22.3 Part I) under the base of all of our poles (about 14" in diameter for you Americans!). We try to ensurr that 'good' soil (or added bentonite) rather than crushed stone is under the plate, which is pressed against the copper plate by the weight of the pole and atachments.

If we know that we have >6 per km (~10 per mile) of these in our system, each bonded to our system neutral, then we do not add rod electrodes, even at transformer poles.

Our empirical tests of this setup usually results in <6 Ohms using IEEE Greet Book fall-of-potential earth resistance test.

 

[stevenal]

We use ground rods. The neutral connection does not count as a ground. NESC has a grandfather clause that allows installations that met former codes to continue, but new installations must meet present code.