Coding is the part of the 2391-52 that separates candidates who have learned four definitions from candidates who can actually inspect. The definitions take five minutes to memorise. Applying them to an observation you have never seen phrased that way before is the skill being examined.
The four codes
| Code | Meaning | Action required |
|---|---|---|
| C1 | Danger present, risk of injury | Immediate remedial action required |
| C2 | Potentially dangerous | Urgent remedial action required |
| C3 | Improvement recommended | Advisory |
| FI | Further investigation advised | Advisory |
These come from BS 7671 Appendix 6.
The question that settles most decisions
Nearly every coding decision reduces to one distinction:
Is the danger present now, or is it potential?
If a person could be hurt by the condition as it stands today — with nothing else having to fail first — it is a C1. If they could be hurt when something else fails, and the installation is not in a safe condition for that fault, it is a C2. If the installation is safe as it stands but falls short of what the current edition would require, it is a C3.
That single test resolves the two comparisons candidates find hardest.
Exposed live conductors vs missing RCD protection
Bare exposed live conductors at a damaged socket are a C1. Nothing else has to fail. Somebody reaching for that socket today is at risk today.
Missing RCD protection where the current edition requires it is a C2. Nothing is exposed. No fault currently exists. But if one develops, it will not be cleared quickly enough to prevent a dangerous shock — the installation is not in a safe condition for a fault.
Both are serious. Only one is dangerous right now, and that is what separates the codes.
A disconnected earthing conductor
This one catches people out because it feels like a C2 — nothing is exposed, after all. It is a C1.
Without a connected main protective earthing conductor, the exposed-conductive-parts of the installation cannot rely on the protective device operating during a fault. Anyone touching them during a fault is exposed to a dangerous touch voltage, and the protection that should clear it is simply absent. The danger is not waiting on a future failure — the safety measure is already gone.
Why C3 matters more than it looks
Here is the rule that the exam tests more reliably than any other:
The overall assessment is unsatisfactory only where a C1 or a C2 is recorded.
Two consequences follow, and both appear in questions:
- A report with a dozen C3 observations and nothing worse is satisfactory. It may make uncomfortable reading, and the client should be encouraged to act on it, but it is satisfactory.
- A report with one C2 is unsatisfactory, however good the rest of the installation is.
If you find yourself wanting to code something C3 and mark the report unsatisfactory because of it, your code is wrong. Work out which it actually is.
Age is not a defect
An installation wired to an earlier edition of BS 7671 is not automatically defective. Periodic inspection asks whether it is in a satisfactory condition for continued service, not whether it would comply if built today.
Older cable colours, correctly identified and safe, are a C3 at most. A consumer unit that met the requirements in force when it was installed is not a C2 simply because a later amendment changed those requirements. Code the danger, not the date.
When to reach for FI
FI is not a severity sitting between C2 and C3. It means the inspection could not reach a conclusion, and something needs looking into without delay.
Legitimate uses:
- an unexplained test reading you cannot account for on the day
- a circuit you cannot trace to its origin
- signs of previous overheating with no identifiable cause
What FI is not for is avoiding a decision you already have enough information to make. If the evidence supports a C2, code it C2. Recording FI to defer an uncomfortable conversation with the client is a failure of the inspection, not a finding of it.
If the further investigation later turns up a C1 or a C2, the overall assessment changes accordingly.
Working the judgement
The way to get good at this is not to reread the definitions — it is to code observations and then check your reasoning against someone else’s.
Our fault coding trainer puts real EICR observations in front of you, asks you to classify each one, and then shows the reasoning behind the correct code. It is free, it needs no sign-up, and the reasoning is the part worth reading even when you got the code right.
For the wider context, the fault coding study guide covers all four codes with worked examples, and the periodic inspection guide covers how the codes feed into the overall assessment.
