How to install and test an earth electrode

Helpful video reference. John Ward (jwflame), an electrician based in Dorset, covers earth electrode installation and loop impedance testing in this practical video. John's content is consistently UK-specific and technically grounded — no filler, just the details that matter. The video demonstrates exactly what the test readings mean and how to assess whether an installation is acceptable under BS 7671.

1. Understand TT earthing and why this matters

In the UK, most urban properties use TN-C-S earthing (also called PME — Protective Multiple Earthing). The earth is connected back through the DNO's supply cable. Rural and older properties supplied by overhead power lines often use TT earthing, where the earth connection is made entirely through an electrode driven into the ground on the premises.

Without a sound earth electrode in a TT system, there is no fault current path. A fault that should cause an RCD to trip quickly might not, or the voltage on the earth terminal could rise to a dangerous level. Getting the electrode resistance low enough for the RCD to respond within the trip time is the core requirement.

2. Confirm the earthing system

Before touching anything, confirm the earthing system type. Look at the consumer unit earth terminal and trace the earth conductor. In a TT system the earth conductor should run outside to a buried rod — you may find an inspection pit cover near the building, or a green/yellow cable disappearing through the wall into the ground. In a TN-C-S system the earth connects back to the meter terminal or the DNO's tail.

If there is any doubt, the definitive test is to measure earth fault loop impedance (Ze) at the consumer unit origin. A very high Ze reading (hundreds of ohms) confirms TT. A low Ze (typically under 1 ohm) confirms TN-C-S. Only an electrician with a multifunction tester or loop impedance tester can do this reliably.

3. Choose the electrode location and type

The most common electrode for UK domestic installations is a copper-clad steel rod, typically 1.2 m long with coupling pieces available to extend it. Position the rod outside the building, at least 1 m from any foundations, in soil that stays reasonably damp throughout the year. Avoid rocky ground, gravel or areas that drain very freely, as these give higher resistance readings.

Before you dig or drive anything into the ground, contact your utility providers to check for buried services. The free Dial Before You Dig service (0800 688 588) covers gas, electricity, water and communications. This is not optional — hitting a buried cable is a serious risk.

4. Drive the electrode

Fit the driving ferrule to the top of the first rod section to protect the thread from the hammer blows. Drive the rod into the ground with a lump hammer or, for stony ground, a dedicated driving head that distributes the impact more evenly. When the top of the rod is near ground level, remove the ferrule, thread on a coupler, attach the next rod section if needed, refit the ferrule and continue driving.

Most domestic installations aim for at least 1.2 m depth. In areas with sandy or free-draining soil, 2 m or more may be needed to achieve an acceptable resistance reading. Where a single rod does not give a low enough resistance, a second rod can be installed at least 3 m away and the two connected together — parallel rods give a lower combined resistance than one rod alone.

5. Connect the earth conductor

Clean any soil from the top of the rod. Fit the manufacturer's earth rod clamp — a split-bolt or saddle-type clamp designed specifically for the rod diameter. The clamp must make solid metal-to-metal contact with the rod and with the earth conductor.

The earth conductor should be at least 16 mm² green/yellow for a domestic installation, run in conduit or with mechanical protection wherever it is above ground level. Where the conductor runs from the electrode into the building, seal the wall entry against moisture and pests. Connect the conductor to the main earthing terminal inside the consumer unit or at the meter position.

6. Fit an inspection access point

Fit a small inspection pit, flush-mounted plastic box or a durable marker over the top of the electrode so it can be found and tested in future. EICRs specifically require an electrician to be able to verify the earth electrode is in place and to test it — if the electrode is buried under paving or landscaping with no access, that will be flagged as a C3 or C2 defect.

7. Test the installation

Using a multifunction tester or dedicated earth electrode tester, measure the resistance of the electrode itself (Ra) and the earth fault loop impedance at the consumer unit origin (Ze). For a TT installation protected by a 30 mA RCD, BS 7671 requires that Ra does not exceed 1667 ohms — but in practice you want it well below this, ideally under 100 ohms, to provide a safety margin for seasonal variation in soil resistance.

If the Ze reading is very high, a second electrode may be needed. The electrician issuing the EICR or installation certificate will record the measured Ze value and confirm the RCD will respond within the required trip time under a fault.

When to call us

This is a job for a qualified electrician in most cases. The physical driving of a rod into the ground is straightforward, but confirming the earthing system type, selecting the right electrode depth, running the conductor correctly and testing the finished installation with proper equipment all require both knowledge and test equipment that most homeowners do not have. Richard covers EICR inspections and earthing work across Sandwich and east Kent.