The concept of earthing system as per BNBC- Bangladesh National Building Code.

As a part of the safety and standard sweep in the textile factories in Bangladesh, as an auditor I have visited more than dozens of facilities. I have seen that they are totally unaware of the importance of earthing, in some cases we were astonished that in an LT panel with 800amp breaker and 600amp current drawing system they have used 10rm earthing cable.

There concern is that this a total loss of adopting higher size earthing as it is never used! They have no provision of retest the integrity of the earthing pit, they even don’t know where the earthing pit and in some cases pit is covered by concrete.
But as per BNBC – Bangladesh National Building code there is clear statement of earthing cable, pit, regular testing interval requirements.

BNBC 2.8.2 Circuit and System Earthing

Earthing definitions- as per BNBC-

Earthing associated with current carrying conductors is normally essential for the security of the system and is generally known as system earthing, while earthing of non-current carrying metal work and conductor is essential for the safety of human life, animals, and property and it is generally known as equipment earthing.

The three main elements required for an earthing system are Earth Conductors, Earthing Lead and Earth Electrodes.

Earth Conductors in panel and to circuits

Minimum Cross-sectional Area of Copper Earth Conductors —in Relation to the Area of Associated Phase 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)
Less than 16 Same as cross-sectional area of phase conductor but not
less than 14 SWG (3.243 mm²)
16 or greater but less then 35 16
35 or greater Half the cross-sectional area of phase conductor

NB- 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.

Restriction-
Aluminium or copper clad aluminium (clad (PP of clothe) – sojjito) conductors shall not be used for final connections to earth electrodes.

Earth Lead

Earth lead is the link which provides connection between the earth conductor(s) and the earth
[alvaa]electrode(s). 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).

In normal provision the earthing lead connects the earth electrode to a bus bar called earth bus bar. earth conductor is connected to Earth bus bar

Earth Electrodes

The earth electrode shall, as far as practicable, penetrate into permanently moist soil preferably below ground water table. The resistance of earth electrodes shall not be more than one ohm.The following types earth electrodes are recognized for the purpose of Code -Copper rods,Copper plates, Galvanized iron pipes.Copper rods shall have a minimum diameter of 12.7 mm.Copper plates shall not be less than 600 mm x 600 mm in size, with 6 mm thickness.GI pipes shall have a minimum diameter of 50 mm.

Rod earthing as per bnbc
Rod earthing as per bnbc

Plate earthing as per BNBC
Plate earthing as per BNBC

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