Earthing
Plain English. Practical detail. UK context.
Earthing connects relevant exposed conductive parts of an electrical installation to its main earthing terminal, forming part of the protective arrangement against electric shock. It is not the same as protective bonding. The earthing system must be understood and verified; the presence of a green-and-yellow conductor alone does not prove effective protection.
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).
The fault path matters
A metal enclosure can become live if an electrical fault occurs. In a correctly designed protective arrangement, earthing contributes to the fault-current path so protection can operate appropriately. The design depends on the supply and installation, not just the size of a visible wire. Earthing arrangements commonly described as TN-S, TN-C-S and TT are not interchangeable labels. The network operator's information and actual site assessment help establish the arrangement, which can be particularly important when adding outdoor equipment or new loads.
Earthing versus bonding
The IET distinguishes exposed conductive parts, which form part of electrical equipment, from extraneous conductive parts which can introduce a potential from outside the installation. Earthing and protective bonding address these different concepts. Not every piece of metal furniture needs a wire attached, and a bonding clamp on a water pipe does not create a substitute earth for new wiring. Misusing the terms can result in unnecessary work or a dangerous assumption about a protective path which does not exist.
What a homeowner should know
If a report identifies missing or inadequate earthing, ask the electrician to explain the affected arrangement and the required action. Do not disconnect unfamiliar conductors during plumbing or decorating. A water service being changed from metal to plastic may alter conditions which need an electrical assessment. Keep records of supply or consumer unit changes, particularly where several businesses have worked on the property. A photograph can help locate equipment, but it cannot establish conductor continuity or measured performance.
For design, alteration and verification
The IET's earthing and bonding FAQ cautions that typical network impedance values are not a substitute for actual site information. BS 7671:2018+A4:2026 is the current installation standard. Designers must assess the existing arrangements before an addition or alteration and select suitable protective measures for the real system. Changes involving the distributor's equipment need the appropriate network involvement, not unauthorised work at the supply head. Record the basis of the design and verification so a later installer can understand it rather than infer the system from cable colours or an old label.
Frequently asked questions
Can a water pipe be used as the earth for new wiring?
Do not assume so. Earthing must be designed and verified for the installation; plumbing can be altered or include non-conductive sections.
Is an earth rod required at every house?
Not simply because it is a house. The correct arrangement depends on the supply, installation and the equipment being added.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.