ELE/Specific Hazards/TBT-ELE-013

Earthing and Bonding Awareness

Electrical Safety › Specific Hazards › Earthing and Bonding Awareness

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Earthing provides a safe path for fault current to flow to ground, enabling protective devices to operate.
Bonding connects exposed metalwork and extraneous conductive parts to ensure they remain at the same potential.
Without proper earthing, a fault on equipment can make its metal casing live at mains voltage.
Main protective bonding connects incoming services such as gas, water, and oil to the main earthing terminal.
Supplementary bonding provides additional protection in high-risk areas such as bathrooms and swimming pools.
BS 7671 (IET Wiring Regulations) sets out the requirements for earthing and bonding in the UK.
Construction sites use TN-S, TN-C-S, or TT earthing systems depending on the supply arrangement.
Temporary electrical installations must have earthing verified before the supply is energised.
Damaged or disconnected earthing and bonding conductors create hidden lethal hazards.
Earth fault loop impedance testing confirms the earthing system will operate protective devices quickly enough.

Electric shock prevention	Earthing and bonding ensure fault current triggers protective devices rapidly, preventing fatal electric shock.
Fire prevention	Inadequate earthing allows fault currents to flow through unintended paths, generating heat and causing fires.
Legal requirement	BS 7671 and the Electricity at Work Regulations 1989 require adequate earthing for all electrical installations.

Don't

Verify earthing arrangements are in place before energising any temporary supply
Ensure main bonding conductors are connected to gas, water, and oil services
Test earth fault loop impedance to confirm protective devices will operate correctly
Use correctly sized earthing and bonding conductors as specified in BS 7671
Inspect earthing connections during routine maintenance and after alterations
Label main earthing terminals and bonding connections clearly for identification
Install supplementary bonding in bathrooms and other special locations as required
Report any disconnected or damaged earthing conductors immediately
Ensure temporary site supplies have earth electrodes tested and recorded
Brief electricians on the earthing system type before starting installation work

DON'T energise any circuit without confirming the earthing system is connected
DON'T remove or disconnect bonding conductors during other trade activities
DON'T use undersized earthing conductors that cannot carry fault current safely
DON'T assume plastic water pipes mean bonding is not required — check BS 7671
DON'T paint over or conceal earthing connection points where they cannot be inspected
DON'T connect earth conductors to structural steelwork without engineer approval
DON'T ignore earth fault loop test results that exceed maximum permitted values
DON'T bypass RCD protection because nuisance tripping suggests an earthing problem
DON'T work on earthing systems without appropriate electrical competence
DON'T leave earth electrodes unprotected where they could be damaged by excavation

See also: Electrical Safety Awareness | RCD Protection and 110 Volt Use

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