A contractor phoned me last winter, annoyed. His CoC had been refused on a warehouse extension and he wanted a second opinion. The new distribution board was neat, the cable sizing was correct, the circuit breaker discrimination had clearly been thought about. And the earth continuity conductor to the extension had been terminated on a painted steel stanchion.
The refusal was correct. It is also, by a distance, the most common substantive finding I write up under SANS 10142-1.
Why additions are where it goes wrong
New installations get designed. Additions get bolted on, often by someone who was not on site for the original work and who has no drawing to work from.
Edition 3.3 is explicit that the earthing and bonding of the installation must be verified as a whole, not just for the new portion. The practical consequence is that the moment you extend an installation, you inherit responsibility for confirming that the existing earthing arrangement is sound. Most disputes I get called into come down to a contractor who priced for the extension and did not price for the verification.
That is a commercial mistake before it is a technical one. Put the verification in the quote as a separate line, and if the client declines it, you have a written record of why you are not issuing a CoC.
The four things I check first
Continuity of the earth conductor, measured, not assumed. A low-resistance ohmmeter, on the actual conductor, from the earth bar to the furthest point. I have found breaks in armouring used as the sole earth path more times than I can count, usually where a gland was fitted without a proper earth tag or where somebody replaced a section of cable and gave up on the armour bond.
Bonding of extraneous conductive parts. Water pipes, structural steel, the metal roof sheeting on a modern industrial building. Painted or galvanised surfaces need to be cleaned back at the bonding point. A bolt through paint is a decorative connection.
The earth electrode and its arrangement. Especially where a TN-C-S supply has been assumed on a rural or semi-rural site because that is what the previous installation did. Confirm what the supply authority actually provides. Getting this wrong on a site with a standby generator produces genuinely dangerous outcomes.
Whether the main earthing conductor is still adequately sized for the installation as it now exists. The extension increased the maximum demand. The main earth was sized for what was there in 2007.
Earth leakage: two recurring errors
The first is protection coverage. Every socket outlet circuit and every circuit supplying a portable appliance needs earth leakage protection. What I find is a new subboard fed from an existing board where the earth leakage unit was left out because the fitter assumed the upstream device covered it — and the upstream device is either a 100 mA unit or has been bypassed after nuisance tripping.
The second is testing. The test button on the unit proves the mechanism operates. It does not prove the trip time or the actual operating current. An instrument test at rated and five times rated, with the times recorded on the test report, takes four minutes and is what distinguishes a real verification from a walkthrough.
Cumulative standing leakage is the reason so many earth leakage units on older commercial boards have been quietly defeated. If you find one bypassed, the answer is usually to split the circuits across multiple units, not to fit a higher-rated device and hope.
The test report is the defence
When a CoC is challenged after an incident, the document that decides the argument is the annexure with the test results. Blank fields, ticks instead of readings, or a report that clearly reproduces the same values across every circuit will not survive an insurer's assessor.
Record the instrument used, its calibration date, actual measured values for continuity, insulation resistance, polarity and earth leakage operating time, and the date of test. If you have a legitimate reason for a departure, note it and reference the clause.
The bit contractors resist most
You cannot issue a CoC for part of an installation. You are certifying the installation you have worked on, and if the existing portion is not compliant you either fix it, exclude it properly, or do not sign.
That conversation with a client who wants to occupy on Monday is difficult. It is considerably less difficult than the one that follows a fire where your name is on the certificate and the test report is thin.