C2 or C3? The one question that decides it

The C2/C3 boundary is the most argued line in periodic inspection. One question decides it: is this potentially dangerous as it stands — or is it just not how we’d build it today? Potentially dangerous is C2. Merely outdated is C3.

The question, unpacked

C2 means a fault or a foreseeable event could turn the defect into real danger — even though nobody is being hurt right now. C3 means the installation departs from the current edition of BS 7671 but there is no credible path from “as found” to “someone gets hurt” while it remains in its present condition. If you can describe the realistic sequence of events that ends in a shock or a fire, you are looking at a C2.

Worked examples

• No RCD protection to socket circuits likely to supply portable equipment outdoors — C2 territory. The foreseeable event (a damaged lead, a mower cable) is exactly what the RCD exists for.
• No supplementary bonding in a bathroom, but all circuits RCD-protected and the other conditions of Reg 415.2 met — usually C3. The protection the bonding would have provided is being delivered another way.
• Cracked accessory faceplate with internals accessible — C2 if live parts could be reached or could become reachable; C3 if it is cosmetic damage with barriers intact. Look, don’t guess.
• Old colours, no circuit identification, missing labels — C3 on their own. Untidy is not dangerous.

Where sparks go wrong

Two failure modes, both common. Over-coding — reaching for C2 to cover yourself — inflates unsatisfactory reports, erodes trust with customers, and dilutes the meaning of the code. Under-coding — C3 “to be helpful” on something genuinely risky — puts your signature against a defect you have downplayed. The honest question from the top of this page beats both instincts.

Back your judgement with the reg

Whatever you decide, cite the regulation the defect offends. A coded observation with the reg number behind it is a professional judgement; one without is an opinion. Best Practice Guide 4 is the calibration tool the industry uses when the line is genuinely fine — read it, then make the call. It is your name on the report.