Earthing and Bonding: Two Different Jobs, Often Confused

Why it matters on a project

Earthing and bonding are the parts of an electrical installation that do nothing at all until the day they are needed, and then determine whether a fault is an inconvenience or an injury.

They are also the parts most easily damaged by subsequent work, because they consist largely of conductors connected to metalwork that later trades cut, move and replace.

The two functions

	Earthing	Bonding
Purpose	Let fault current return so protection operates	Keep touchable metalwork at similar potential
Protects against	Prolonged fault, fire, equipment damage	Dangerous touch voltage during a fault
Connects to	Earth electrode system	Other metalwork and the main earth terminal
Failure mode	Protection does not operate fast enough	A person bridges two different potentials
Substitutes for the other?	No	No

What fit-out work tends to break

This is where the subject becomes practical for anyone running an interiors project:

• A bonding conductor disconnected to move a pipe, not reconnected
• A metallic pipe section replaced with plastic, breaking continuity that something downstream relied on
• New metalwork — partitions, raised floors, trunking — installed without being brought into the bonding arrangement where required
• Earth conductors damaged or omitted at new distribution boards
• Earth pits built over, paved across or made inaccessible for testing

None of these produces a symptom. The installation energises and works. The deficiency is only discovered by inspection and test, or by a fault.

Common mistakes

• Treating earthing and bonding as the same thing. They protect against different events.
• Disturbing bonding during fit-out without recording it. What is not recorded is not reinstated.
• Building over earth pits. They need to remain accessible for testing and maintenance.
• Testing once at handover and never again. Earth resistance changes with ground conditions over time.
• Improvising separate earths for IT equipment. Without proper design this can create the hazard it was meant to avoid.
• No test records at handover. Inspection and test documentation is how anyone later knows what was actually installed.

Standards referenced

Earthing practice in IS 3043; electrical installation practice in IS 732; building services provisions in NBC 2016, Part 8. Earthing system design, bonding requirements, test values and the testing regime for a specific installation must be established by the project's electrical consultant and verified by inspection and test.