Compound Demarcation or separations of compounds may use metallic fences sometimes for saving money or aesthetic reasons. Architects and owner of the project decide whether their property protected by compound wall or it needs only fencing. If fencing considered, most cases it will be metallic fence. In the electrical point of view and as a safety measure, metallic fence shall be separately earthed unless they come within 1.8 m of any equipment or structure above the surface of the ground, which is connected to the main earthing system. If the separation of 1.8 m cannot be obtained the fence shall be bonded to the earthing system. Here is how compound fences connecting to the earthing system.
1. Separately Earthed Fences
The earthing of a fence shall be provided by connecting certain metallic fence posts to an earth rod by a copper conductor. The earth rod shall be driven adjacent to the posts inside the fence line to a depth of not less than 3.0 m. Where no metallic posts are provided the earth rods shall be connected directly to the metal wires, mesh or other components of the fence.
2. Earth Bonded Fences
Fences which need to be bonded to the main earthing system of the installation shall be connected by copper conductors to the nearest accessible point on the main earthing system at each point where the fence comes within 1.8 m of any electrical equipment. Bonds shall also be made to each comer post, below the outer phase conductors of overhead line connections passing over the fence, at each gate and at intervals of not more than 100m.
Earth Bonding of Fence Components
- Fences made up of bolted steel or other metallic components do not require bonding between components. Where such fences have non-metallic components bonds shall be installed to maintain continuity between metallic components. Reinforced concrete components shall be treated as being non-metallic.
- Longitudinal wires for supporting other fence components or for anti-climbing guards and the wires of chain link shall be directly bonded to each fence earth electrode or to each bond to the main earthing system.
- Metallic components on masonry, brick, concrete or similar boundary wall shall be treated in the same manner as metallic fences.
- Wire fence components coated for anti-corrosion protection or PVC coated fence shall be earthed in accordance with this Clause.
Earth Bonding of Metallic Fencing Gates
The fixed metallic components on both sides of the gate shall be directly bonded together by a copper conductor installed under the surface of the access way. Flexible conductors shall be installed to bond the moving parts of the gates to the metallic fixed parts. An earth rod or a bond to the main earthing system shall be installed at each gate.
Electrical Potential Control Outside Fences
- Where the approved design calculations show that the touch or step potentials outside the fence or boundary wall would otherwise be excessive, bare copper conductors shall be buried in the ground outside the fence or boundary wall at such depths and spacing as are shown in the approved design calculations to give acceptable touch and step potentials.
- The conductors shall form complete rings surrounding the installation and each ring shall be bonded to the adjacent ring and to the fence at each comer. Below the outer phase conductors of overhead line connections passing over the fence, at each gate and at intervals of not more than 100 m. In this case separate earth electrodes are not required for the fences.
- If the boundary fence or wall is substantially non-metallic the rings of conductors shall be bonded to the main earth system at each corner of the site and at intervals of not more than 100 m. Any metallic components on If the boundary fence is metallic and is not within 1.8 m of any part of the main earthing system or equipment bonded thereto the fence and outer conductor rings shall not be connected to the main earthing system unless the approved design calculations show otherwise.
- Any meshes formed by bonding the outer conductors to the main earthing system shall be sub-divided by additional conductors, if required, to give acceptable touch, step and mesh potentials.
Earthing Conductors for Metallic Fences
All conductors used for earthing and bonding the fences and components and for outer rings shall have a cross-sectional area of not less than 185 mm2 copper.