Height of 132 Overhead Line

[Sparkyman]

I am trying to design a lightning protection system for a building and want to claim protection by the earth wires of 132kV overhead lines above.
I've done the calcs to BS6651 and know the minimum height that the cables must be to give protection, however I don't know the actual cable height. The electricity company aren't that helpful and if I measure it with a theodolite I don't know what the maximum sag will be.
So, what is the minimum height allowable above a building of a 132kV overhead line?
What is the height above that of the earth cable? (they are double circuit towers (if that is the right term))

 

[ItAintMe]

Depends what country/state you are in. The minimum clearances are usually specified by your national standards authority or electricity regulator. In Australia, our minimum clearnce to ground is 6.7 - 7.6 metres depending on ground type - trifficable or not. Tower lines are usually quite a bit taller in built up areas to allow for lower voltage distribution circuits running along the streets below them. so maybe around 11 metres minimum.

 

[jghrist]

The best way is to measure the actual height of the shield wire at the points needed. You could do this with a theodolite located perpendicular to the line. If you measure on a hot day, you will get the maximum sag. The height and sag of shield wires will vary a lot depending on the particular line design and terrain.

The utility might be able to provide profile of the line. I'm sure they would rather have you prove that the line provides the necessary shielding than have someone up on a roof anywhere near their line installing lightning rods.

 

[MikeDB]

The NESC recommends a minimum of 15.4' for 132kV (line to line) over roofs accessible to pedestrians. There is no standard for how high the static wires are above that. Depending on the height of the building, a stroke could hit the side of the building. IEEE Standard 998 discusses shielding.