Earthing & bonding
Connecting exposed metal to earth so a fault blows protection fast and metalwork can't become live.
What it does
Earthing connects the exposed metal parts of an installation to earth. If a live conductor touches that metal, earthing gives the fault current a low-resistance path back — so protection operates quickly and the metalwork doesn't stay live for someone to touch.
How it works
A protective earth conductor runs with each circuit to the metal parts. On a fault to earth, a large current flows through this low-resistance path, tripping the breaker or RCD fast. Bonding ties together other metalwork (pipes, structure) so everything sits at the same potential and there's no dangerous voltage between parts.
If the earth path is poor (a loose or undersized connection, high loop impedance), the protection may not operate fast enough — a serious safety issue.
Why it matters
Earthing and bonding are fundamental safety systems. RCDs add protection by detecting leakage to earth before it becomes lethal. A high earth-fault loop impedance reading means the protective path isn't good enough and must be rectified.
Safety first
Earthing is a primary safety system — a poor earth or high loop impedance is dangerous and licensed work to rectify. Never remove or compromise earthing.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Related faults
High earth-fault loop impedance / earthing concern
Testing shows a high earth-fault loop impedance (or an earthing concern) on a circuit — meaning protection might not operate fast enough on a fault, which is a safety issue to resolve.
RCD / RCBO keeps tripping
An RCD or RCBO trips repeatedly — immediately on reset, randomly during the day, or only when certain equipment runs. The earth-leakage protection is doing its job; something is leaking.
Loose connection overheating (discolouration / smell)
A terminal or connection is overheating — discoloured insulation, a burning smell, or heat you can feel — a common cause of nuisance faults and a real fire risk.
Related definitions
RCD (safety switch)
Detects earth leakage and disconnects fast to protect people from electric shock.
Neutral vs earth
The neutral carries return current; earth is for safety. Confusing them causes real, dangerous faults.
Circuit breaker (MCB)
Automatically disconnects a circuit on overload or short circuit, and can be reset rather than replaced.