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 -protected and the main bonding is in place, which is itself a favourite exam point.
Where to look it up: BS 7671 Section 701.
Where Supplementary 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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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.
Main protective bonding
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Main 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 Main protective bonding entryRCD — Residual Current Device
A safety switch that compares the current going out on the line conductor with the current coming back on the neutral. If they differ, current is leaking somewhere it should not, possibly through a person, and the RCD cuts the supply in a fraction of a second. Most socket circuits in UK homes need RCD protection, usually rated at 30 mA.
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