Earth resistance test: what is tested, when it is due and who may sign in South Africa
Headcore
In short
An earth resistance test measures, in ohms, how well an earth electrode connects to the ground, usually by the fall-of-potential method. In South Africa the Electrical Conformance Board's CoC test report template records earth continuity, earth loop impedance and earth leakage tests, not electrode resistance. The Electrical Installation Regulations set no ohm value; installations must comply with SANS 10142-1.
What does an earth resistance test measure?
An earth resistance test measures the resistance of an earth electrode to the ground around it, in ohms. The UK wiring regulations (BS 7671), as quoted by the IET, define earth electrode resistance as "the resistance of an earth electrode to Earth".[10]
The usual method is fall of potential: a three- or four-terminal tester is connected to the electrode, to a temporary test electrode driven some distance away and to intermediate potential spikes between them, and reads the electrode's resistance from the voltage drop.[10]
The reading depends on the soil and the electrode: seasonal changes in moisture change it, and the length of a rod affects its resistance far more than its diameter. Buried metalwork such as structural steel or water pipes can lower a reading, but the IET warns it cannot be relied on as the electrode, because it may be removed or replaced later.[10]
For an existing electrode, the resistance can only be found by measuring it: at a periodic inspection its construction and buried location are usually unknown, and it may have corroded.[10]
Which earth tests go on a South African CoC test report?
In South Africa a certificate of compliance (CoC) must come with a test report (Electrical Installation Regulations, regulation 7(1)). The Electrical Conformance Board's test report template for general installations to SANS 10142-1 records the earth tests below; it has no line for earth electrode resistance.[1][9]
| Test on the report | Recorded as | Template line |
|---|---|---|
| Continuity of bonding | Ω, compliant or not applicable | Test 1 |
| Resistance of the earth continuity conductor at every point of consumption | Ω, listed on annex pages | Test 2 |
| Earth loop impedance at the main or a local switch | Ω | Test 4 |
| Voltage between the incoming neutral and an external earth, measured with load applied | V | Test 7 |
| Operation of earth leakage units | Tripping current in mA | Test 11 |
| Earth leakage test button | Correct or not | Test 12 |
Sources:[9]
When does earthing have to be tested in South Africa?
Earthing is tested whenever a certificate of compliance is needed. A registered person may issue one only after satisfying himself or herself "by means of an inspection and test" that the installation complies (Electrical Installation Regulations, 2009, regulation 9(2)), and the Electrical Conformance Board's test report template includes the earth tests in the table above.[1][9]
The first time is before connection: no completed or partly completed installation may be connected to the supply "unless it has been inspected and tested by a registered person and a certificate of compliance for that electrical installation has been issued" (regulation 8(2)).[1]
After the first connection, the Electrical Installation Regulations call for a new CoC, and so a new inspection and test, in these cases:[1]
- an addition or alteration: a CoC "for at least the addition or alteration" (regulation 7(4));[1]
- an installation from before 23 October 1992 that has not changed owner since 1 March 1994: a CoC for the whole installation at its first addition or alteration (regulation 7(3));[1]
- a change of ownership: the user or lessor may not allow it if the CoC is older than two years (regulation 7(5));[1]
- a fault or defect found by an inspector, an approved inspection authority or the supplier, who may then require a new CoC (regulation 7(7)).[1]
How often should earthing be tested?
In South Africa, the Electrical Installation Regulations set no fixed retest interval for an installation in use. They make the user or lessor responsible for "the safety, safe use and maintenance" of the installation (regulation 2(1)), and a new test follows the events that call for a new CoC: an addition or alteration, a change of ownership where the CoC is older than two years, or a defect found (regulation 7).[1]
Construction sites have a fixed interval, for inspection rather than testing. Under regulation 24 of the Construction Regulations, 2014, the control of every temporary electrical installation is given to a competent person appointed in writing, and every temporary installation the contractor uses is inspected at least once a week by a competent person, with the findings recorded in a register kept on site (regulation 24(c) and (d)).[3]
Who may test earthing and sign the certificate?
In South Africa only a registered person may issue a CoC (Electrical Installation Regulations, regulation 9(1)), and the registration category limits which installations that person may certify.[1]
| Person or case | What the regulations allow | Regulation |
|---|---|---|
| Electrical tester for single phase | Tests and certifies installations supplied by a single-phase supply at the point of control, except specialised installations | 1 and 11(2) |
| Installation electrician | Tests and certifies any installation except specialised installations | 1 and 11(2) |
| Master installation electrician | Tests and certifies any installation, specialised installations included | 1 and 11(2) |
| Specialised installations | Installations in explosive atmospheres (SANS 10086-1), the petroleum industry (SANS 10089-2), hazardous locations (SANS 10108) and medical locations (SANS 10142-1) | 1 |
| Any part above 1 kV | Its design is approved by a competent person under paragraph (b), (c) or (d) of the General Machinery Regulations definition, or by a person registered in a professional category under the Engineering Profession Act, 2000 | 5(5) |
| Approved inspection authority for electrical installations | Inspects and tests only when the user or lessor asks it to or the chief inspector or provincial director contracts it; may not operate as an electrical contractor | 4 |
Sources:[1]
What is a good earth resistance value in South Africa?
The Electrical Installation Regulations give no earth resistance figure. They require every installation to comply with the incorporated standard, SANS 10142-1 (regulation 5(1)), and the registered person tests against it before issuing a CoC (regulation 9(2)).[1][2]
The current edition of the wiring code is SANS 10142-1:2026 (Edition 3.03), approved on 24 June 2026; the Department of Labour's explanatory notes name the incorporated standard as SANS 10142-1 "or any updated revision of the standard".[4][2]
Earth electrodes are the subject of SANS 10199:2016, which gives "authoritative guidance on the methods to be used in providing an earthing system and in calculating and measuring the essential characteristics of earth electrodes". SANS 10292:2013 covers the earthing of low-voltage distribution systems, and lightning protection falls under SANS 10313:2018 and SANS 62305-3:2025, which replaced the 2011 edition.[5][6][7][8]
For UK installations, the IET explains that where the supply authority provides no connection to earth (a TT system), it is generally not possible to disconnect an earth fault in the required time with only an earth electrode as the return path, so a residual current device (an earth leakage unit) is usually installed.[10]
The Electrical Conformance Board's test report template records which system an installation uses (TN-S, TN-C-S, TN-C, TT or IT), has a box for "Supplier's earth is functional", and records the earth loop impedance and the voltage between the incoming neutral and an external earth under load.[9]
What should an earth test report and CoC show?
The CoC, in the form of Annexure 1 to the Electrical Installation Regulations, identifies the installation (physical address, building name, GPS coordinates, erf number), says whether it is an initial or a supplementary certificate, and carries the registered person's declaration that he or she "personally carried out the inspection and testing", with registration number, date of registration and category.[1]
The registered person enters the CoC number on the test report, and the CoC is not valid unless every section is completed correctly and the test report is attached (Annexure 1, declaration and notes).[1]
The Electrical Conformance Board's template also records the rated tripping current of the earth leakage unit (the form prints 30 mA, with space for another value), whether surge protection and lightning protection are installed, and, where lightning protection is installed, refers to the SANS 10142-1 lightning protection system installation safety report (Table I.10). Each reading is entered with the instrument used, and a comment field lists the parts of the installation the report does not cover.[9]
In practice, a separate earth electrode test should record each electrode's location and construction, which the IET notes are usually unknown by the time of a periodic inspection, and the date and soil condition, because seasonal changes in moisture change the reading.[10]
What to put in your request
- The site address and building, the distribution boards and earth electrodes to be tested, and the earthing system if known (TN-S, TN-C-S, TT or another), including whether the installation relies on the supplier's earth or its own electrode.[9][1]
- Why the test is needed: a new installation, an addition or alteration, a change of ownership with a CoC older than two years, or a fault found by an inspector, an approved inspection authority or the supplier.[1]
- The tests wanted: earth continuity at every point of consumption, earth loop impedance, earth leakage trip current and test button, and earth electrode resistance where the installation or its lightning protection has its own electrodes.[9][10]
- Whether any part runs above 1 kV or is a specialised installation (explosive atmosphere, petroleum, hazardous or medical location), since that changes who may certify it or approve its design and adds test reports.[1][9]
- The registered person's name, category and registration number, and sight of the certificate of registration, which a registered person must produce on request.[1]
- For electrode tests: the electrode layout as far as known, space to drive temporary test spikes well away from each electrode, and the date and soil condition written on the report.[10]
- Whether lightning protection is installed and whether its SANS 10142-1 installation safety report (Table I.10) is part of the job.[9]
- Each reading with the instrument used and whether it complies, on annex pages where the form runs out of space, plus a list of anything not covered.[9]
- For a construction site: the competent person appointed in writing for the temporary installation and the weekly inspection register.[3]
Questions buyers ask
Is earth leakage testing the same as earth resistance testing?
No. An earth leakage test checks that the earth leakage unit trips: the CoC test report template records its tripping current in mA and whether its test button works. An earth resistance test measures an earth electrode's resistance to the ground in ohms, with a three- or four-terminal tester and temporary test spikes.[9][10]
Does a certificate of compliance expire?
The Electrical Installation Regulations give a CoC no expiry date, but a user or lessor may not allow a change of ownership if the CoC is older than two years (regulation 7(5)), and any addition or alteration needs a CoC for at least that work (regulation 7(4)).[1]
Can someone other than our electrical contractor check the earthing?
Yes. The user or lessor may ask an approved inspection authority for electrical installations, accredited by SANAS and approved by the chief inspector, to inspect and test the installation, and such an authority may not operate as an electrical contractor (regulations 3 and 4). A CoC itself can only come from a registered person (regulation 9(1)).[1]
Does a temporary supply on a construction site need testing?
Yes. Regulation 24 of the Construction Regulations, 2014 applies in addition to the Electrical Installation Regulations, so the temporary installation is inspected, tested and certified by a registered person before it is connected, and is then inspected at least once a week by a competent person, with the findings in a site register.[3][1][9]
Sources
- Department of Labour (Government Gazette 31975), Electrical Installation Regulations, 2009 (GN R.242), 6 March 2009.
- Department of Labour (Government Gazette 35180), Explanatory notes on the Electrical Installation Regulations, 2009 (General Notice 258 of 2012), 26 March 2012.
- Department of Labour (Government Gazette 37305), Construction Regulations, 2014 (GN R.84), 7 February 2014.
- SABS, SANS 10142-1:2026 (Ed. 3.03), The wiring of premises Part 1: Low-voltage installations, 24 June 2026.
- SABS, SANS 10199:2016 (Ed. 2.02), The design and installation of earth electrodes, 14 March 2016.
- SABS, SANS 10292:2013 (Ed. 2.00), Earthing of low-voltage (LV) distribution systems, 26 July 2013.
- SABS, SANS 10313:2018 (Ed. 3.03), Protection against lightning: physical damage to structures and life hazard, 18 July 2018.
- SABS, SANS 62305-3:2025 (Ed. 3.00), Protection against lightning Part 3: Physical damage to structures and life hazard, 2 September 2025.
- Electrical Conformance Board of South Africa, Test report for all general electrical installations to SANS 10142-1 (template), undated, read November 2026.
- IET (Institution of Engineering and Technology), Inspection and testing of earth electrodes, undated, read November 2026.