Main protective bonding
Plain English. Practical detail. UK context.
Main protective bonding connects relevant extraneous conductive parts to the installation's main earthing terminal to reduce the risk of a hazardous potential difference. Incoming metal services are a familiar example, but the need is assessed from the actual arrangement. Bonding is not the same function as earthing electrical equipment.
Safety: use a registered electrician, for example one registered with a competent person scheme such as NICEIC or NAPIT, for electrical installation work. Do not remove covers or open electrical equipment yourself.
Last reviewed: (editorial review against the public sources listed below).
Why the terminology is important
The IET explains that an extraneous conductive part can introduce a potential, generally earth potential, without being part of the electrical installation. The purpose of protective bonding is therefore different from the fault path associated with exposed conductive equipment. A wire fixed to random metal objects is not evidence of a sound protective design. Conversely, a pipe that appears to be ordinary plumbing can matter electrically if it introduces a potential into the building.
Plastic services and common misunderstandings
It is a misconception that every water pipe needs main protective bonding. The IET notes that a plastic incoming service which has no fortuitous earth contact is not an extraneous conductive part. However, the complete arrangement must be established, not guessed from a short visible plastic section under the sink. Other connections or buried metallic sections may affect the assessment. The electrician should explain why bonding is required or not required, rather than simply attaching a clamp because one was seen in a neighbouring house.
Plumbing changes need coordination
Replacing a service pipe, moving a meter or cutting out metal pipework can affect existing bonding. Tradespeople should identify the conductor and coordinate any necessary electrical work before removing it. A plumber's competence in water work does not automatically cover designing and verifying an electrical protective measure. For homeowners, report planned plumbing changes and avoid hiding clamps behind finishes without discussing access. If a report flags a missing connection, arrange the recommended assessment rather than buying a clamp and guessing a conductor size.
Standards, checks and clear handover
BS 7671 sets requirements for protective bonding, including selection and connection arrangements. Use the current edition identified by the IET, not a generic internet wire-size chart. The IET FAQ also emphasises assessment of existing earthing and bonding before additions or alterations. A useful work record identifies what was checked and corrected and any inaccessible elements. Main bonding and bathroom supplementary bonding are distinct questions; finding one does not automatically settle the other. This entry deliberately gives no universal conductor size or clamp location for all supply and service configurations.
Frequently asked questions
Does every metal sink need main bonding?
No. The need follows the electrical definitions and actual connections, not simply whether an object is metal. Have the arrangement assessed competently.
Can bonding be removed after a plastic pipe repair?
Not on that observation alone. The electrician needs to establish the complete arrangement and whether the existing connection remains necessary.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.