Grounding or Earthing system is a connection system between metal and ground from the installation of electrical wiring.It is for provide easy access to a low impedance, or resistance to earthing protection system to operate effectively to ensure the safety of people or users from shock hazards electricity in the event of leakage current to earth.
We should prepared the good design for electrical earthing for electrical installation system.It must follow regulation and standard from IEE or Local authority for electrical.In general, the earthing system for electrical installation.
Grounding or earthing is generally divided into two (2) parts, namely:
1) Grounding System
Isolating the system in the event of damage
To limit the potential difference between conductors that are not insulated in the area.
Limiting the excessive voltage (over voltage) in different conditions.
2) Grounding Equipment
It is made for the protection of human or users.
If a source of power supply affect body equipment, electricity will flow into the earth and will not flowing through the human body or users.
This is because human body has a higher resistance against with resistance to earth.
Grounding Accessory Type and Function
1) Earth electrode
Type of electrodes used for wiring a house or factory is the rod copper-coated steel
2) Equipotential bonding
Conductors are connected between the source of the earth to guide exposed metal parts. Minimum size is 10 mm 2 cable.
3) Protective conductor
Conductors are connected between the source of the earth to other parts of the installation that requires grounding its size is as below:
a) Use same size if phase cable sizes up to 16 mm 2
b) Use size 16mm 2 cable if phases cable size between 16 mm 2 to 35 mm 2
c) Half of the cable size if phase cable size more than 35 mm 2
Standard color code for earthing cable
Green / Yellow
The parts need to grounding or earthing
All metal structure in the wiring system (which is not current carrying) as the metal coating, shielding conduit, ducting,trunking, etc.
One source of secondary winding of the transformer.
Roof frame made of metal (Metal Roof Truss).
The parts no need to grounding or earthing
Short metal isolated as mechanical protection for cable with other non-metallic sheath vessels connected as a gateway between the building and conduit to protect cable discharge lamps.
The lamp cover is made from metal
Lighting equipment for the metal filament lamp on the waterproof floor
Metal chain to hang the lights and equipment.
Termination On Earth Chamber
Earthing or Grounding electrode resistance ( ohm )
Installation earth electrode is covered by the RCD 100mA = 10 ohm
Lightning arrester = 10 ohm
Sub station = 0 – 3 ohm
Consumer installation = 500 ohm