Conduit Riser Clearance 1

[jduesler]

In a substation, what would be the minimum height above grade required for the top of the conduit risers on 25kV feeder exits? I know the minimum clearance above grade is 10' at 25kV, but I was wondering if there were any rules governing the minimum height of the conduit.

 

[stevenal]

Assuming a USA installation, NESC requires 8.5 ft to areas of indeterminate potential unless otherwise guarded. Since anything between ground and phase potential is considered indeterminate, it is best to have at least 8.5 feet to any high ground points with insulation above. Consider arrester grounds and cable concentric neutrals where they exit terminators. I know of no rule specific to conduit, but practicality places the conduit end below the items mentioned above.
"Above grade" isn't really the rule. Since the height is for personnel protection, take your measurements from any handy standing surface, such as foundations.