Earthing & Bonding
Installation · C&G 2365 Units 203/305 · Full course section in Plus
connects an installation's exposed metal parts back to the source, so when a live conductor touches a casing, a large fault flows and the protective device disconnects — that's . Bonding is different: it ties extraneous metalwork like incoming water and gas pipes to the same potential, so a fault can't leave two things you're touching at dangerously different .
The system arrangement — , or TT — decides where that fault path runs and how good it is, which is why the same house rewire can need different protection in different streets.
Our questions drill the distinction, the conductor names and the system types until you can explain them to a customer in one breath — which is roughly what a 2365 assessor wants too.
This guide is free to read. There is no public quiz specifically for this topic yet. Explore the key terms below without leaving the page.
Common questions
- Can I try Earthing & Bonding free on this page?
- This guide is free to read, but there is no public quiz specifically for this topic on this page. Browse public practice samples for other subjects, or create an account for the learning path. The full course section requires Plus.
- Where does Earthing & Bonding sit in the City & Guilds scheme?
- & Bonding maps to Units 203/305. On TradeTraining it lives in the Installation section as bite-size lessons with practice questions.
- What is the difference between earthing and bonding?
- provides a deliberate path for fault back to the source so protective devices disconnect quickly. Bonding connects touchable metalwork together so it all sits at the same potential during a fault. Earthing clears faults; bonding limits the voltage between things you can touch while the fault lasts.
Explore key terms
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Earthing
Connecting an installation's exposed metalwork to earth and back to the supply source. That gives fault current a deliberate low-impedance path home, turning a live casing into a large, brief fault current that the protective device can detect and disconnect — without it, the casing simply stays live.
Read the full Earthing glossary entryMain protective bonding
Conductors connecting incoming metallic services — water, gas, oil, structural steel — to the main earthing terminal. Bonding does not clear faults; it holds the touchable metalwork of a building at roughly the same potential while a fault lasts, so a person touching a pipe and an appliance at the same moment isn't bridging a dangerous voltage difference.
Read the full Main protective bonding glossary entrySupplementary bonding
Additional local bonding between simultaneously accessible conductive parts, classically in bathrooms. It is used where disconnection times or other conditions for protection can't otherwise be met. In modern installations it can often be omitted when the circuits are RCD-protected and the main bonding is in place, which is itself a favourite exam point.
Read the full Supplementary bonding glossary entryCPCCircuit Protective Conductor
The earth wire of a circuit. It links the metal parts of the equipment the circuit feeds back to the main earthing terminal. It is not the normal load-current return path, although equipment can produce protective-conductor current in normal operation. During an earth fault it provides a path for fault current, working with the earthing arrangement and protective device to achieve disconnection. In UK wiring it is green and yellow, or bare inside twin-and-earth cable, with green-and-yellow sleeving wherever it is exposed.
Read the full CPC glossary entryTN-C-SProtective Multiple Earthing (PME)
The most common modern UK supply arrangement: the distributor combines neutral and earth in a single conductor (the PEN) up to the service head, where it splits into separate neutral and earth for the installation. Its weakness is a broken PEN conductor, which can put the whole installation's earthed metalwork at a dangerous voltage — the reason special rules apply to EV charging and other outdoor equipment on PME supplies.
Read the full TN-C-S glossary entryTT system
An earthing system where the installation provides its own earth via an electrode in the ground. Common on rural and overhead supplies, it takes no earth from the distributor at all. The soil path makes the earth fault loop impedance high, so an RCD, not the overcurrent device, is what disconnects earth faults on a TT installation.
Read the full TT system glossary entry