"franz frippl" wrote in message
news
I need advice in placing grounding rods when upgrading electrical service
from 100 amp to 200 amp.

Code requires at least 2 5/8" x 8' rods placed no closer than 6'.

Soil conditions: sandy loam. Water table is about 15-18' below grade.

I am considering stacking rods so I will end up with 2 16' rods.

Question is how close can these be without compromising effectiveness of
grounding system?


No less than 6'. There are rods made that have the ends threaded to add
length. I think that they are available from McMaster-Carr;
http://www.mcmaster.com

You can also buy 3/4" x 10' ground rods at some electrical supply companies.

As another posted stated a distance of 16' or more from each other is
optimal for 8' rods. If the rods are longer they should be further apart.
If you are very concerned about soil resistively you could always install 3
or 4 rods.