Overhead line clearances

[Todd0x1]

Here are (some of) California's rules on overhead high voltage lines. There is an old structure directly under some transmission and distribution lines with more than 12ft vertical clearance. Trying to figure out if the same thing could be built today.

(c) Clearance from Buildings. Open high-voltage conductors shall be substantially supported independently of buildings or structures and shall have a clearance from buildings or structures as follows:
(1) They shall be maintained not less than 6 feet horizontally from buildings or other structures or any portion thereof. Where the vertical distance above ground of conductors of 7,500 volts or less is in excess of 35 feet, this horizontal clearance from buildings shall be permitted to be less than 6 feet, but shall be not less than 4 feet.
(2) They shall be kept not less than 12 feet vertically above any part of buildings or structures over which they pass.

I find this a bit confusing. If you have to have 6 feet horizontal clearance, then how can lines pass over a building with 12 feet of clearance? If the line is 6 horizontal feet from the building, then it would not pass over the building.

Or is the horizontal clearance specifically for buildings next to lines where the vertical clearance doesnt exist? For example a tall building next to some power lines?

 

[paulengr]

Not sure about California but OSHA has a 10 foot rule that increases with voltage in some regulations, and is fixed in others, but drops to 4 feet below a line while driving under it.

All of these are generally derived from IEEE 514.(? think that's the right one) and has to include lots of dustance for swinging in the wind and stretching in heat or under ice loads. The minimum clearance is 10 feet in all directions but does get narrower for instance at a pole where line spacing is fixed and the issue becomes accessibility. Like directly under a pole we usually assume a person is 6 feet tall with an 8 foot reach. Then add clearance onto that for fixed structures (Usually 3.5 feet) which we can round up to 10-12 feet.

So yes you may be seeing different conditions applying.

NESC has much more extensive guidelines with tons of pictures for roads, buildings trains, multiple use poles, etc. That is the Code generally followed by utilities. I'm sure if you dropped the "conditions" out of NESC it would read like the regulation.

There was a math error found a few years ago. The clearances over 25 kv have increased.

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