Alan,
What have you found out so far?
From a post from resqcapt19 on another topic we get this information: http://www.highvoltageconnection.com/articles/highvoltagespacing.pdf
And form what it looks like it is saying to me is [Linked Image]138 kv*3)/10000= 41.4 inches minimum spacing for bare conductors.
I hope that this helps and that I understand this properly.
Tim