Fence Likely to become energized?

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ed downey

ed downey

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Missouri
I have a Security fence that has a Utility Line (Not sure of the voltage at this point) running over the top of it (approximately 3' above the top of the fence).

Is this considered "Likely top Become Energized"?

What section would cover the Requirement for Grounding?

Is there a NEC or NESC requirement for the Line to be at a certain distance above teh top of the fence?

Thanks,
Ed
 
I don?t think this is so easy, Dereck. The power source that would energize the fence, if it is indeed ?likely? to do so, is the utility. How do we bond the fence in such a way as to create an ?effective ground fault current path? back to the utility?s upstream source?

Also, is a line 3 feet above the fence ?likely? to energize the fence? How about a line 2 feet, or 4 feet, or any other distance you choose to name? The basic question here is whether the NEC requires a minimum distance from a utility line and a fence. I don?t think the NEC is going to have anything to say on this question.
 
The Fence is about 10' tall (8' Shain link with about 2' of Barbed wire) and the Line is about 3' above the fence.

I do not know the voltage but it is probably 12,470V.

-Ed
 
The first question is - is the utility happy with having something that close to it's MV lines? In NZ our equivalent (11KV) lines require a minimum clearance of 5.5m to structures, unless you get engineering advice from the utility.
 
wireman71 said:
I would think the metal poles sunk in concrete are better bonding anyways..
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Better than what? A wire, connected to a fence post and connected to the neutral (or at least the down ground) at the pole would be best. I'm pretty sure that fence could be bonded, have a bolted fault to that OH conductor, completely evaporate, and the primary's OCPD will not open. Just a guess, but they size utility OCPD's to protect their most expensive stuff, and not really to clear little piddley faults. With some luck, there might be a recloser that will snap out. That takes 3 tries, normally. That fence might be pretty well messed up, and any person that might have been involved would be crispy fried. Something just doesn't seem right about the conductor actually being of the voltage the OP proposed.
 
charlie b said:
I don’t think this is so easy, Dereck.
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You are probable right, I pulled the trigger a little quick. My thinking was in respect to my little world where we have these nasty things called thunderstorms, tornados, and ice storms that make things fall out of the sky.
 
I the utility line is 12.46 kv and only 13 ft above the ground, that will not be up the the utility specs. You need to contact them and have it checked.
 
13' is way to low for those lines, from the site description it sounds like a lot or field with a fence around it, it would seem any 18 wheel trucks or a vehicle with any king of large antennae would definitely be close if not hit those lines. I would say consult the utilities engineer, although you may not like what they have to say.
 
You can find the required clearances over a fence in 225.61, a FPN claims that Table 225.61 is in 'harmony' with the NESC as well.

225.61 Clearances over Buildings and Other Structures.
(A) 22 kV Nominal to Ground or Less. The clearances over buildings and other structures for conductors and live parts up to 22 kV, nominal, to ground or less shall be not less than the values shown in Table 225.61.

(B) Over 22 kV Nominal to Ground. Clearances for the categories shown in Table 225.61 shall be increased by 10 mm (0.4 in.) per kV above 22,000 volts.
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Minimum height for 22 kV or less is 7' over 'other structures'

225.60 gives us the minimum heights over land which range from 14.5' to 26.5'
 
Thanks for the information. The overhead line is the Utility feed to a transformer at a Prison in Texas. I do not have any pictures at this time but since we are adding on to the Prison part of the scope of work I think should be to install this line underground.
 
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