What ACCORD & BNBC stated about Earthing!!!

 ACCORD & BNBC Stated  about Earthing:   

10.10 Earthing

10.10.1 General. 

In general all parts of equipment and installation other than live parts shall be earth potential, thus ensuring that persons coming in contact with these parts shall also be at earth potential at all times.

10.10.2 Circuit and System Earthing.

10.10.2.1 Circuit and system earthing shall limit excessive voltage from line surges from cross-overs with higher voltage lines or turn lighting and keep non-current carrying enclosures and equipment at zero potential with respect to earth.

10.10.2.2 The value of the earthing resistance shall be in accordance with the protective and functional requirements of the installation and be continuously effective.

10.10.2.3 Where a number of installations have separate earthing arrangements, protective conductors running between any two of the separate installations shall either be capable of carrying the maximum fault current likely to flow through them or be earthed within one installation only and insulated from the earthing arrangements of any other installation. In the latter circumstances, if the protective conductor forms part of cables the protective conductor shall be earthed only in the installation containing the associated protective device

10.10.3 Methods of Earthing.

10.10.3.1 General. 

The three main elements required for an earthing system are earth conductors, earthing lead and earth electrodes.

10.10.3.2 Earth Conductors.

10.10.3.2.1 Earth conductors are the part of the earthing system which joins all the metal parts of an installation.

10.10.3.2.2 In all cases the grounding conductor shall be made of copper or galvanized steel or other metals or combination of metals which will not corrode excessively and, if practical, shall be without joints or splice. If joints are unavoidable, they shall be made and maintained so as not to materially increase the resistance of the earthing conductor and shall have appropriate mechanical and corrosion resistant characteristics.

10.10.3.2.3 Aluminium or copper clad aluminium conductors shall not be used for final connections to earth electrodes.

10.10.3.2.4 The earth conductor shall have a short time capacity adequate for the fault current which can flow in the grounding conductor or conductors for the operating time of the system protective device. In case of copper wire being used as earth conductors, the size of the wire shall not be less than half the area of the largest current carrying conductor supplying the circuit.

10.10.3.2.5 BNBC Table 8.2.11 gives the minimum sizes of copper earth conductors corresponding to the sizes of associated copper circuit conductors. No size smaller titan 14 SWG shall be used anywhere as earth conductor.

 

BNBC Table 8.2.11

Minimum Cross-sectional Area of Copper Earth Conductors in Relation to the Area of Associated Phase Conductors

Cross-sectional Area of Phase Conductor(s) (mm2)	Minimum Cross-sectional Area of the Corresponding Earth Conductor (mm2)
Lessthan16 16orgreaterbutlessthan35 35orgreater	Same as cross-sectional area of phase conductor but not less than 14SWG  16 Half the cross-sectional area of phase conductor

10.10.3.3 Earth Lead.
10.10.3.3.1 The earth conductor shall be brought to one or more connecting points according to size of installation; the copper wire earthing leads shall run from there to the electrodes.

10.10.3.3.2 Earthing lead can either be of copper wire or of copper strands.

10.10.3.3.3 Earthing leads shall be run in duplicate down to the earth electrode so as to increase the safety factor of the installation. Copper wire used as earthing lead must not be smaller than 8 SWG (12 mm2).

10.10.3.4 Earth Electrodes.
10.10.3.4.1 The earth electrode shall as far as practicable penetrate into permanently moist soil preferably below ground water table. The resistance of the electrodes shall not be more than one ohm.

10.10.3.4.2 The following types earth electrodes are recognized: Copper rods, copper plates, galvanized iron pipes.

10.10.3.4.3 The following is a guideline for electrode size: Copper rods shall have a minimum diameter of 12.7 mm,GI pipes shall have a minimum diameter of 50mm, copper plates shall not be less than 600 

(NOTE: The whole topic has been taken from ACCORD book)