Main protective bonding
Conductors connecting incoming metallic services — water, gas, oil, structural steel — to the main 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 difference.
Where to look it up: BS 7671 Chapter 41.
Where Main protective bonding fits in the learning path
The Installation section covers these units:
- Wiring Systems & Enclosures
- Cable Selection & Circuit Design
- Earthing, Bonding & Consumer Units
Curriculum mapping: C&G 2365 Units 203/204/305.
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- Earthing & BondingInstallation
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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.
Supplementary bonding
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Supplementary 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 Supplementary bonding entryEarthing
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 Earthing entryTN-C-S — Protective 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.
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