# power towers



## TransientCW (Oct 26, 2012)

are power towers that hold those power lines insulated on their legs, or is the entire tower grounded itself? i havent been able to find much regarding this on any relevant websites.

im curious if towers themselves are grounded, what prevents current from arcing straight to the tower itself? i may be getting a lineman apprentice gig and i am curious about new things.


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## 3DDesign (Oct 25, 2014)

I'm no expert on towers but my understanding is they are grounded and so is the top conductors. Insulators and distance prevent arcing.


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## glen1971 (Oct 10, 2012)

The ones I've worked on have been grounded extensively, including the rebar throughout the base.. The top line/two lines are grounding conductors as well.. If I remember right one of the lines on one set was a fibre optic line from one sub to another..


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## CADPoint (Jul 5, 2007)

If you study and look at a power tower the power never touches the tower itself. The power is held of by insulators, and the count (amount) of insulators varies depending on the voltage through the circuits on a tower.

You have to go study any sub-station how the the ground is brought down from the top of the tower, in that it's part of the service.

I'd have to go study how the ground at the top is held to the tower... 

Your getting into Step potential when dealing with either a tower or a sub -station. That's why they heavy "ground" both a tower and a sub station.


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## Meadow (Jan 14, 2011)

These tower are rarely if ever isolated from earth, if anything youd want a low impedance path to trip protective relays.


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## 37523 (Dec 30, 2012)

The tower is usually the highest thing around. The top wires are the next highest thing around. They WILL attract lightning. The only thing you can do with lightning is take it to earth as direct and as well as possible. 

Line-to-dirt faults are a second issue. You'd like to trip-out if a line taps the tower. However in my area of thin dirt over dense rock, it may be hard to find a threshold between Heavy Load and Dirt Fault because of high ground resistance (despite extraordinary dirt-bonding). Up where the line crosses Bill's Bog the low resistance of the swamp may give great trip-currents.


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## chrisfnl (Sep 13, 2010)

The grounded wire that runs along the the highest point of the towers isn't installed in all locations, we have a very low occurrence of lightning strikes around here, so they only install the overhead shield wire within 2 km of larger sub stations on long distance transmission lines, no OSW on smaller local transmission lines between local sub-stations.

To the OP, towers should always be firmly grounded, not just for lightning strike protection, but also fault protection, and to prevent inducted voltage in the tower.

I've never installed or maintained them, but I'd assume they have a radial ground or grounding network of some sort as well, rather than a single point ground.


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