10.3 Observation Classification Codes C1/C2/C3/FI

The Four Observation Codes

Every observation recorded on an EICR is classified with one of four codes defined in GN3 and BS 7671:

These codes drive both the overall outcome of the report and the urgency with which the client must act. Choosing the correct code is one of the most heavily tested topics in the 2391-52 exam.

C1 — Danger Present

A C1 means there is immediate risk of injury — the installation is unsafe to leave as found. The inspector must take appropriate action to make safe: typically isolating the dangerous part from the supply and warning the user not to use it. The client must be notified immediately — orally at the time of the inspection and in writing on the EICR. Examples include:

• exposed live conductors accessible to touch;
• a circuit with metal accessories (Class I equipment) that has no earthing — a fault would make the metalwork live;
• a consumer unit in a dangerous physical condition (charred, arcing, or physically broken).

A C1 is the most serious code and always makes the report unsatisfactory. Leaving a C1 unreported, or failing to take action to make safe, is a serious failure of the inspector's duty.

C2 — Potentially Dangerous

A C2 means the defect is not immediately dangerous but could become so under foreseeable conditions — so urgent remedial action is required. Examples include:

• Zs exceeding the maximum permitted by BS 7671 Table 41.2 or 41.3 — the disconnection time may not be met under fault conditions;
• an RCD failing to operate within its time limit at IΔn — the fault protection or additional protection it provides is not effective;
• a broken earth conductor on a circuit not currently in use but which could be energised.

The line between C1 and C2 is actual danger versus potential danger: is someone at risk right now (C1), or only if a fault occurs (C2)? A circuit with no earthing and metal accessories is C1 because a fault makes the metal live immediately; a circuit with high Zs is C2 because danger arises only when a fault occurs and the device does not disconnect in time.

C3 — Improvement Recommended

A C3 means the item does not present danger but improvement is recommended. Crucially, C3 does NOT make the report unsatisfactory. Examples include:

• a circuit that predates the RCD requirement and does not strictly need one under current BS 7671, but an RCD would improve safety;
• missing identification labels or circuit schedules;
• a switch mounted slightly too high for convenient access.

The line between C2 and C3 is danger versus mere improvement: if the defect could become dangerous, it is C2; if it is merely sub-optimal and presents no danger, it is C3. A common exam trap is coding a missing RCD as C2 when the circuit does not require one under BS 7671 — where there is no requirement and no danger, C3 is correct.

FI — Further Investigation Advised

FI means the inspector could not fully determine the safety or condition of the item without more invasive investigation — typically removing fixtures or fittings, or accessing concealed wiring. The item needs further examination by a competent person. Examples:

• a circuit whose terminations are concealed inside a sealed accessory and could not be inspected without dismantling;
• a cable route that could not be traced and whose earthing continuity could not be confirmed;
• a consumer unit interior that could not be accessed because the cover was sealed by the supply authority.

FI is used when the inspector has done what is reasonably possible but uncertainty remains that needs more work to resolve.

The A4:2026 change to FI and the outcome rule

Under BS 7671:2018+A4:2026, an FI code does NOT by itself make the report unsatisfactory. Appendix 6 has been reworked so that Section K (observations) is split into two parts:

• Part 1 — C1 and C2: observations that make the overall outcome UNSATISFACTORY.
• Part 2 — C3 and FI: advisory observations that do NOT affect the overall outcome.

The wording of FI was also softened: where it previously said further investigation was "required without delay", A4:2026 says further investigation is "advised". The purpose of FI is unchanged — it flags an apparent deficiency that cannot be fully assessed within the agreed scope — but it is no longer treated as automatically equivalent to a C2 for the bottom-line outcome.

This is a change from the previous rule. Under BS 7671:2018+A2:2022 (and A3:2024), any C1, C2 or FI made the report unsatisfactory. A4:2026 (published 15 April 2026, the sole standard from 15 October 2026) decoupled C3 and FI from C1 and C2 so that an advisory uncertainty no longer tips an otherwise sound installation into "unsatisfactory" territory.

Professional judgement still applies. FI is not a guaranteed "pass": if the inspector genuinely suspects that, once investigated, the item would prove to be a C1 or C2, an unsatisfactory outcome remains appropriate. The reasoning should be recorded. But the blanket rule "FI always fails the EICR" is the pre-A4 rule and is no longer correct under the current standard.

The Outcome Rule (Exam-Critical)

Under BS 7671:2018+A4:2026, the overall outcome of the EICR is determined by the codes present:

• UNSATISFACTORY if ANY C1 or C2 code is present.
• SATISFACTORY if only C3 and/or FI codes (or no observations) are present.

A single C3 or FI does not, by itself, make the report unsatisfactory; a single C1 or C2 always does. This rule is the most tested point in the observation-coding section of the exam. Remember: the outcome follows the codes — the inspector does not choose it independently.

Watch the amendment. If your exam sitting or study material still references the pre-A4 rule, you will see "unsatisfactory if any C1, C2 or FI". That was correct under A2:2022/A3:2024 but is superseded under A4:2026, where FI and C3 are decoupled from the outcome. Confirm which amendment applies to your sitting, but answer to the current standard unless told otherwise.

Worst Code Wins and Multiple Defects

Where a single item has more than one defect, it is recorded under the most serious applicable code — the worst code wins. For example, a socket-outlet that both has a cracked faceplate (C3) and no earthing (C1) is recorded as C1, with the faceplate noted in the observation text. The inspector does not split one accessory across two codes.

Where several separate items each have defects, each gets its own code and its own line on the schedule of inspections. A single circuit can therefore generate several observations at different codes — for instance, a ring final circuit with high Zs (C2) and a missing RCD where one is not strictly required (C3). The report lists both, and the overall outcome is driven by the most serious code present across the whole installation — here, the C2 makes it unsatisfactory.

A practical tip for the exam: when given a scenario, first ask "is anyone in danger right now?" (C1), then "could this become dangerous under a fault?" (C2), then "is this just an improvement?" (C3), and finally "could I not see enough to judge?" (FI). This four-step ladder maps directly onto the four codes and avoids the common error of jumping to C2 for anything that looks less than perfect.