Type B earthing which is Ring or Foundation earthing meets all the requirements of a lightning Protection system for complex buildings & buildings located in rocky area. It helps in conduction of lightning current to earth, Equipotential bonding of all down conductors and controlling potential near the building. Type B earthing shall be either a ring earthing or foundation earthing embedded in the concrete. In Ring earthing, Earthing conductor shall be buried preferably 0.5 meter below and 1 meter away from the external walls of the building. 80 percentage of the conductor shall be below the soil , so that the installation shall be considered as ring earthing , otherwise it can be considered only as a Type A earthing ( Vertical electrode). Generally a Type A earthing is applicable for small buildings like family houses. Ring earthing is possible in existing buildings and helps to control the dangerous ground potential rise when the lightning current is dissipated to ground. A combination of ring earthing and SPD (Surge Protective Device) is the best practice to ensure protection of electrical system and the people protection inside the building
Concrete used for the foundations of buildings has good conductivity and generally a large contact area with the soil. Therefore bare metal electrodes completely embedded in concrete can be used for earthing purpose. The hygroscopic characteristics of concrete generally produce a sufficiently low earth electrode resistance. If the reinforcement of the concrete and any other steel constructions of a structure are connected both externally and internally so that the electrical continuity & against physical damage is achieved.
Interconnected reinforcing steel in concrete foundations or other suitable metal structures should preferably be used as an earth electrode. When the metallic reinforcement in concrete is used as an earth electrode, special care shall be exercised at the interconnections to prevent mechanical splitting of the concrete. In a typical Industrial plant,a number of associated structures are nearby , and a large number of power and signal cables are installed in between the buildings. The earth terminations systems of such structures are very important for the protection of the electrical systems. A low impedance earth system reduces the potential difference between the structures and so reduces the interference injected into the electrical lines. The reinforcing rods of the foundation, foundation slab and outer walls in the region below the soil surface of such structures form an excellent foundation earth electrode. The magnetic field generated by the current in the reinforcing steel mesh is weak due to the low current density and the parallel current paths generating opposing electromagnetic fields. Also, interference with neighboring internal electrical conductors is correspondingly reduced. The reinforcing rods of the foundation and the buried walls used as a foundation earth gives good earthing at minimum cost. In addition this system offers good potential references to the electric power supply, telecommunication and electronic installations of the structure. A connection from the steel reinforcement shall be brought outside concrete by a rust free material and shall be used to connect ring earthing, vertical earthing and the protective conductor from the equipment.
The continuity of the reinforcing rods should be established by clamping or welding (with the permission from civil engineer). Where welding the reinforcing rods is not permitted/possible, clamps or additional conductors should be used & bonded with the steel reinforcement with the clamps tested for the requirements of IEC 62561-1. These additional conductors can be made of steel, mild steel, galvanized steel or copper.
Meshed earth termination system gives a low impedance between buildings and has significant EMC advantages. The size of the meshes near to the building shall be in the order of 20 x 20. Beyond a 30m distance they may be enlarged to the order of 40 x 40m.
In General, implementing foundation or ring earthing is easy and economical, if it is planned at initial stages of a project. A proper coordination among LPS designers and installers, architect, builder and electrical system designer is required to achieve best result at minimum cost.