What to know about foundation earthing

[edit] Introduction

The concept of foundation earthing – installing earth electrodes as a closed ring in the foundations of buildings – is by now familiar. What foundation earthing means in practical terms is perhaps less well understood.

[edit] Establishing a mandate

When the Draft for Public Comment (DPC) for the 18th Edition Wiring Regulations (BS 7671: 2018) was opened in 2017, a mandate for foundation earthing was proposed, though this never made it into the final edition.

The DPC for Amendment 2 of the Regulations, which closed in December 2020 and is under review as of May 2021, has reintroduced the concept once more.

It is worth clarifying at this point that proposals in the DPC are liable to change. There is no guarantee any proposal will be included in the final draft. Foundation earthing is nevertheless an important concept, and we will nod to the wording used in the DPC.

[edit] DPC clarifications

The DPC states in Regulation [IP address hidden] that (and I paraphrase) for new installations constructed upon foundations, some form of additional earthing will be required. Three options are proposed:

• Concrete-embedded foundation earth electrode.
• Soil-embedded ring earth electrode.
• Equivalent electrode using metalwork of a steel framed building.

Additional information was provided in an informative annex.

Essentially, the idea is to connect the earthing system of a building to an additional earth, using foundation rebar or a ring electrode in the soil. This can prevent significant voltage increases in event of a fault.

[edit] Harmonising foundation earthing approaches

Proper foundation earthing involves a certain amount of coordination between the electrical contractor and those involved in the construction of the foundations, to ensure that components work in harmony.

If you ever come to discuss foundation earthing with German or French peers, you may find them incredibly well-versed on the subject. Unlike current British Standards, European Standards for foundation earthing are many and detailed, right down to recommended types of soil, concrete and connections.

But for now, in the UK, foundation earthing is not essential, though you may come across it. BS 7430, the code of practice for protective earthing of electrical installations, gives information on foundation earthing should an electrical designer or installer wish to find out more.

Future editions of the wiring regulations may well require designers and contractors to implement more foundation earthing systems, though this will not be clear until Amendment 2 is released in 2022.

This article originally appeared on the ECA website. It was written by Gary Parker, ECA Technical Manager and published on 4 May 2021.

--ECA

[edit] Related articles on Designing Buildings Wiki

• 18th Edition Wiring Regulations.
• Articles by the Electrical Contractors' Association (ECA).
• Comparison of SMM7 with NRM2.
• Earthing.
• Electrical wiring.
• Energy related products regulations.
• Radial circuit.

[edit] External resources

• BSI, BS 7430:2011+A1:2015, Code of practice for protective earthing of electrical installations.
• Institution of Engineering and Technology, Updates to 18th Edition.