Security fencing grounding

[damshawn]

I am Maintenance Electrical Engineer at a federal multipurpose hydroelectric dam and am not as intimately familiar with the 70 as I could be. I am trying to find good justification for management to properly ground the new security fencing around our federal hydroelectric facility. I walked out the fencing and found that the old fencing was periodically grounded but the new fence has nothing that I can find. As we are in a windy dry area with periodic lightning strikes, I am concerned that the fencing should be grounded but I cannot find it specifically in the 70. Is it located in a section under something else or is it even directly addressed? I know that it is the right thing to do but I also need to justify spending the man-hours on this. Thank you in advance for any help.

 

[dereckbc]

Re: Security fencing grounding

These type of facilities are not covered by NEC, rather NESC. Security fences are grounded to the grid in substation and power generation stations. It is not done for lightning but rather to clear a fault in the event of an overhead line falling onto the fence, or to protect human and livestock life in the event there is a ground fault inside the secured area from step rise potential.

[ June 08, 2004, 10:41 AM: Message edited by: dereckbc ]

 

[damshawn]

Re: Security fencing grounding

Just as clarification, this security fence is not associated with the generation nor the transmission as this is the exterior physical security fence. The boundary that crosses under our transmission lines is the river. The fence in question is actually a 1/4 mile away and in no way electrically connected to the power house. This only protects the resources area and storage yard. Sorry for the insufficient info.

 

[dereckbc]

Re: Security fencing grounding

Wish I could give you some ammo with NEC requirements, but there is none unless you have a gate controller or some other electrical device. In that event all that would be required is an EGC ran with phase and neutral conductors, or just the raceway itself used as an EGC.

Your really talking about a design/performance issue.

 

[websparky]

Re: Security fencing grounding

Here is some info from NFPA 780 Standard for Lightning Protection Systems.

D.1.4
Fences built with metal posts set in the earth are as safe from lightning as it is practical to make them, especially if the electrical continuity is broken. Breaking the electrical continuity is very useful in that it reduces the possibility of a lightning stroke affecting the entire length of a fence, as is possible if the stroke is direct and the fence continuous, even though it may be grounded. The fences that give rise to the most trouble are those constructed with posts of poorly conducting material, such as wood.

D.3.1
In addition to grounding the fence, its electrical continuity should be broken by inserting insulating material in breaks in the wires at intervals of about 500 ft (150 m). These insertions can be in the form of fence panels of wood or lengths of insulating material to the ends of which the wires can be attached. Such lengths of insulating material can consist of strips of wood about 2 in. 2 in. 24 in. (50 mm 50 mm 600 mm), or their equivalent as far as insulating properties and mechanical strength are concerned.

I would also recommend this web site:
http://www.lightningsafety.com/

 

[msd]

Re: Security fencing grounding

what kind of fence? metal obviously but is it chain link, rod iron, barbed wire? a little more info please........