Study the 2391-52 by practising the decisions an inspector of existing installations makes: distinguish periodic inspection reasoning from initial verification, apply the observation codes C1, C2, C3 and FI to ambiguous defects, justify the extent and sampling you declare on the report, and complete the paperwork consistently. Work through written defect scenarios and self-mark against a rubric.
Periodic inspection reasoning is a different mode from initial verification
Initial verification confirms new work meets design and BS 7671 requirements. Periodic inspection judges an existing, aged installation: you assess condition, code defects, and recommend a next inspection instead of issuing an electrical installation certificate.
Carry that distinction into your study notes. For initial verification the questions centre on completeness: every circuit tested, every result compared against expected values. For periodic inspection the centre of gravity moves to assessment: what condition is this installation in after years of use, deterioration and alteration, and can it safely remain in service until remedial action or the next inspection?
Practise by re-reading any initial-verification-style notes you have through a periodic lens. Ask of each topic: how does this change when the installation is twenty years old, has undocumented alterations, and no design information is available? For example, comparing measured earth fault loop impedance against a tabulated maximum becomes judgement about whether the value gives the required disconnection for the protective device actually fitted, which may not be the one originally designed.
- Certificate of new work: electrical installation certificate, all results recorded.
- Report on existing installation: EICR, observation codes, extent and limitations declared.
- Study trigger: for each test topic, write one sentence on how aged equipment alters your interpretation.
Where C1, C2, C3 and FI actually blur
The four observation codes grade danger and urgency: C1 danger present, C2 potentially dangerous, C3 improvement recommended, FI further investigation needed. Ambiguity sits between C2 and C3, and between C2 and FI, so practise those boundaries.
The distinctions hinge on evidence and immediacy. A C1 means someone could be harmed right now, so the code should describe an immediate hazard. A C2 means a fault exists that could become dangerous, but nothing requires instant action. A C3 records something not unsafe today but worth improving. FI is not a softer code for uncertainty about severity; it records that a part of the installation could not be inspected or tested sufficiently to reach a code at all.
Build a personal decision tree: is there immediate danger? Then C1. If not, is there a fault likely to lead to danger? Then C2. If neither, is an improvement still worthwhile? Then C3. Only if you cannot obtain enough evidence to code at all, because of access, operational limits or safety, do you record FI and explain why in the report. Test yourself with ambiguous cases, such as minor corrosion, missing labels, or older cable colours, and check your reasoning against the example classifications in your current edition of Guidance Note 3.
| Code | Meaning | Typical trigger in study scenarios | Effect on the report outcome |
|---|---|---|---|
| C1 | Danger present | Live parts accessible without tools; conductor arcing | Unsatisfactory; immediate action expected |
| C2 | Potentially dangerous | Fault could cause danger but not immediately; failed RCD with no present hazard | Unsatisfactory; remedial work needed |
| C3 | Improvement recommended | Non-compliance that is not unsafe, such as a missing notice | Does not alone make the report unsatisfactory |
| FI | Further investigation needed | Part could not be safely or practically inspected or tested | Report cannot fully cover that part; treat as not assessed |
Extent and sampling: the decision you must justify in writing
An EICR is only valid for the extent you state. Study how to agree the extent and any sampling with the person ordering the work, record it clearly, and extend the sample when results reveal problems.
Periodic inspection of a large installation rarely covers every accessory, so the report records what percentage or which circuits were examined. Practise drafting extent statements: name the parts included, the parts excluded and the reason for each exclusion, and note any sampling agreed. The skill being trained is proportionality: a defensible sample on a large, well-maintained installation is reasonable; a thin sample used to save time without agreement is not.
Link sampling to the codes you find. If your sampled circuits throw up a significant defect, that is evidence the same fault may exist elsewhere, so the professional response is to widen the sample and say so in the report rather than to code the single defect and move on. Rehearse writing that decision in two sentences: what you found, and what you changed about the extent as a result. This habit transfers directly to any written task that hands you partial survey data.
- Draft an extent statement for a two-storey office before any testing.
- State the sampling percentage agreed and who agreed it.
- Record in the report any area excluded because access was denied or operations prevented it.
- When a sample finds a C1 or C2 defect, extend the sample and document the extension.
Worked scenario: coding a residual current device that will not trip
A socket circuit's 30 mA RCD fails to operate during testing. The tempting mistake is to code C1. The better decision is C2 where no immediate hazard is present, with FI considered only if testing could not be completed.
Scenario: during a periodic inspection you press the RCD test button, then carry out an instrument test on a final circuit, and the device does not trip at or near its rated residual current. The people in the building are not being shocked right now; they simply lack a working additional protective function. The quick learner codes C1 because the word 'failed' feels severe. That overstates the immediacy and undermines the report: if every serious finding is a C1, the reader cannot prioritise genuine emergencies.
The better decision: no danger is present at the moment, so record C2, describing precisely what failed and on which circuits, and note the recommendation for remedial work. If access or site conditions meant you could not complete the residual current tests on some circuits at all, record FI for those parts and explain why. The reason this matters is the downstream effect: a C2 makes the overall classification unsatisfactory and triggers remedial action, a C1 triggers immediate action, and a careless C1 can cause unnecessary shutdown. Mirror this structure when you practise: state the finding, justify the code, state the effect on the report.
Worked scenario: the sample that uncovers a circuit in poor condition
You inspect a 10 percent sample of lighting circuits and find a damaged point and a disconnected protective conductor. The mistake is recording two codes and closing the report; the better decision is to widen the sample and record the change of extent.
Scenario: on a warehouse periodic inspection the agreed plan is a 10 percent sample of lighting circuits. One sampled circuit has a damaged ceiling rose, and another shows the circuit protective conductor not connected at a light fitting. The narrow reading is: two defects, code them C2, job done. But the disconnected protective conductor suggests a pattern, perhaps a botched alteration affecting other circuits in the same area, and your sample is no longer representative.
The better decision is to increase the sample for the affected circuits and, once the fuller picture is known, code the worst representative findings and state in the report that sampling was extended after initial findings. The classification may then rest on multiple confirmed defects rather than one. Why it matters: the report is the client's evidence of condition and their basis for remedial planning and safety management. A report that quietly stops at the first two defects leaves known-unknown faults undocumented, and a written task on this topic rewards the inspector who shows the extend-the-sample reasoning explicitly.
Turning inspection findings into EICR paperwork answers
Set yourself a mapping exercise: take a list of defects and results and, for each, choose the right report section, the right code, and a next inspection recommendation with a stated reason.
Train on the flow from observation to documentation. Every finding needs: where it is (the report reference for that circuit or location), what it is (a precise description), the code, and the recommended action. Vague descriptions such as 'wiring poor' would not survive moderation; 'damaged insulation on cooker circuit cable within 300 mm of the socket outlet, C2' would. Write full descriptions for ten defects from a scenario sheet and check each one answers a reader's questions of where, what, and how dangerous.
The recommendation of a next inspection interval is a judgement, not a fixed rule: it depends on the findings, the environment, how the installation is used and maintained, and information from the dutyholder. Practise writing one-sentence justifications, for example recommending an earlier re-inspection where a C2 remains unremedied or where the environment is harsh. Avoid single-figure memorised intervals for settings you have not assessed; the skill worth training is the justification, and published guidance in your current BS 7671 supporting material shows typical ranges rather than universal answers.
- Every coded observation: location reference, precise description, code, action.
- Classification is unsatisfactory where C1, C2 or FI findings exist; C3 alone does not force that outcome.
- Next inspection recommendation: state the reasoning, not just a number.
- Limitations section: record what was not inspected and why, in plain language.
A preparation sequence and self-check rubric for 2391-52
Sequence your study in four passes: code theory, extent and paperwork, scenario drilling, then a timed mock with self-marking. Use the rubric below to decide when you are ready to book, and confirm administrative details with City & Guilds directly.
Practical exercise: write or obtain ten paper defect descriptions for a single fictitious installation, such as a small hotel. For each, record your code, a one-sentence justification, and the effect on the overall classification. Then attempt the EICR front page: extent statement, limitations, and a next inspection recommendation with reasoning. Mark yourself against this rubric, and treat the scores as learning milestones, not predictions of any grade: three points for a code that matches your current edition of Guidance Note 3 examples, two for a justification citing the specific hazard, two for a precise location description, two for a consistent classification outcome, and one for a justified next inspection recommendation.
Adaptable sequence: weeks one and two, read the inspection, testing and reporting sections of your current BS 7671 and Guidance Note 3 and summarise the code boundaries in your own words. Week three, drill the scenario exercise above daily and draft extent statements for three different building types. Week four, attempt a timed written mock, mark it with the rubric, and repeat any section scoring under nine out of ten. Readiness checks: you can code ten varied defects with consistent justifications, you can state and defend an extent and sampling plan, and you can complete the report paperwork unaided without looking up section names.
- Rubric total 10: codes (3), hazard justification (2), precise descriptions (2), classification consistency (2), next inspection reasoning (1).
- Aim for 9+ before moving from scenario drilling to timed practice.
- Re-read your own written descriptions once after a day's gap; vagueness is easier to spot cold.
- Administrative details such as assessment format and entry requirements change; check them with City & Guilds at https://www.cityandguilds.com/ rather than relying on older course notes.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.