The four EICR classification codes defined in IET Guidance Note 3 Table 3.5, with the BS 7671 regulations behind each code and the common mistakes that get inspectors into trouble.

EICR coding is the classification system used by electrical inspectors to record observations on an Electrical Installation Condition Report. Four codes exist: C1, C2, C3 and FI. Each code carries specific implications for the overall satisfactory or unsatisfactory outcome of the report, the required remedial action, and the legal position of the duty holder. This guide explains every code against the actual BS 7671:2018+A2:2022 regulations, reproduces the classification table published in IET Guidance Note 3, and sets out the most frequent coding mistakes seen on real EICRs.

The Electrical Installation Condition Report (EICR) is produced at the end of a periodic inspection and test carried out under Chapter 65 of BS 7671. Regulation 653.1 states: “Upon completion of the periodic inspection and testing of an existing installation, an Electrical Installation Condition Report based on the model given in Appendix 6 shall be produced.” Every observation recorded in the Observations section of that report must be assigned a single classification code. The code determines whether the installation is deemed satisfactory for continued service, and it drives the remedial-action timetable the duty holder has to follow.

Chapter 65 of BS 7671 governs periodic inspection and testing. Regulation 651.1 sets the purpose: to determine, so far as is reasonably practicable, whether an installation is in a satisfactory condition for continued service. Regulation 651.2 sets the scope and, at item (vi), requires the inspection to identify “installation defects and non-compliances with the requirements of the relevant parts of BS 7671, that may give rise to danger.” Regulation 651.5 requires the work to be carried out by one or more skilled persons competent in such work.

The classification codes C1, C2, C3 and FI are not defined in BS 7671 itself. They are published in Table 3.5 of IET Guidance Note 3: Inspection & Testing (8th Edition, aligned to BS 7671:2018+A2:2022), which is the recognised industry reference for EICR coding. Section 3.11 of Guidance Note 3 is explicit about two things. First, “Each separate item entered in the Section K ‘Observations’ section of the Report should be coded C1, C2 or C3 as appropriate, or exceptionally, FI. Only one classification code is to be recorded against each observation.” Second, “Where an installation defect or non-compliance with the Regulations has attracted a code of C1, C2 or FI, the overall assessment of the Report must be ‘unsatisfactory’.”

A C1 is reserved for observations where there is an immediate risk of electric shock, burn or fire and where the danger cannot be left in place at the end of the inspection. The defining question for a C1 is not “how serious is the fault?” but “is someone at risk of injury right now, before any further event occurs?”

When a C1 is found, the inspector is expected to take immediate action on site. That will typically mean making the defect safe by isolation, applying a danger-live label to the affected circuit, and obtaining written acknowledgement from the client or occupier that the risk has been pointed out. The remedial work itself is then carried out either immediately or to a very short timescale agreed with the duty holder. The overall assessment of the report must be marked Unsatisfactory whenever a C1 is present.

A C2 captures defects that are not immediately dangerous but where a single further fault, event or act could result in danger. The classic test is the “single-fault-to-danger” principle: if one additional failure (an earth fault, insulation breakdown, user interaction) would turn the defect into an injury risk, it is a C2.

Guidance Note 3 lists, among other things, these C2 examples: a non-earthed installation (requires a further fault to result in danger), fundamentally undersized cables, earth fault loop impedance values greater than those required by BS 7671 (see Table 41.1 maximum disconnection times: 0.4 s for a TN final circuit at 230 V AC, 0.2 s for a TT final circuit at 230 V AC, 5 s for a TN distribution circuit, 1 s for a TT distribution circuit), borrowed neutrals, and insulation resistance readings below the Table 64 minimum of 1 MOhm for low-voltage circuits tested at 500 V DC per Regulation 643.3.

A C2 renders the report Unsatisfactory. Under the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020, landlords must complete C1, C2 and FI remedial work within 28 days of the report, or within the shorter period specified on the report itself.

A C3 is applied where the installation does not meet the current requirements of BS 7671 but where the departure does not give rise to immediate or potential danger. Table 3.5 gives four headline examples of C3: absence of most warning notices, absence of the required diagrams and charts, no or incorrect marking of conductors at terminations, and absence of an RCD specified for additional protection where the circuit otherwise tests as normal.

That last example is one of the most frequently miscoded items on EICRs. Absence of 30 mA RCD additional protection on existing socket-outlets up to 32 A (Regulation 411.3.3) or on AC final circuits supplying luminaires in dwellings (Regulation 411.3.4) is a C3 where the circuit otherwise tests as normal. It becomes a C2 only where accompanying circumstances (damage, occupancy, external influences, BS 7671 breach elsewhere on the same circuit) escalate the risk.

FI is applied where the inspection has identified an apparent deficiency that could not be fully assessed within the extent of the inspection agreed with the client. The purpose of an FI is to flag that further investigative work is needed before the true classification (potentially C1 or C2) can be determined.

Table 3.5 gives two example scenarios. The first is where the characteristics of the electricity supply (for example, measured voltage or external earth fault loop impedance Ze) do not conform to supply-industry norms, which may indicate a DNO-side problem that the inspector cannot diagnose on site. The second is where part of the installation inside the agreed scope could not be physically accessed during the inspection (for example, a ceiling void that was boarded over, a locked plant room, or a spur buried behind fitted furniture).

Any FI present on the report renders the overall assessment Unsatisfactory. An FI is identical in effect to a C1 or C2 for the purposes of the overall outcome and the PRS remedial timetable. FI is not a way of avoiding a decision: it is used where the decision genuinely cannot be made with the evidence available inside the agreed inspection scope.

The rule is set by Section 3.11 of Guidance Note 3: any single C1, C2 or FI makes the overall Condition Report Unsatisfactory. A report with any number of C3 observations remains Satisfactory. There is no weighting, no “majority wins”, and no inspector discretion. One C2 on one circuit in a 200-circuit commercial installation still produces an Unsatisfactory overall outcome.

These are the errors most often seen on EICRs that end up disputed, rejected by letting agents or insurers, or challenged by the duty holder. The right coding is not about being harsh or lenient; it is about applying the Table 3.5 test faithfully to what has actually been found on site.

1. Coding absence of 30 mA RCD protection as C2 by default. Where Regulations 411.3.3 (socket-outlets up to 32 A) or 411.3.4 (domestic lighting) are not met on an existing installation and the circuit otherwise tests as normal, the correct code per Table 3.5 is C3. A C2 is justified only where accompanying defects or occupancy factors elevate the risk beyond “improvement recommended”.

2. Coding accessible bare live parts as C2. Accessible bare live parts are the headline Table 3.5 example for C1. There is no “urgent” qualification – the risk is present now, not on the occurrence of a further fault. Code C1 and make safe on site.

3. Coding low insulation resistance as C3. Table 64 of BS 7671 sets the minimum insulation resistance at 1.0 MOhm for low-voltage circuits tested at 500 V DC under Regulation 643.3. Table 3.5 lists “insulation readings under 1 MOhm” as a C2 example. A sub-1 MOhm reading is not “improvement recommended” – it is evidence that insulation is failing.

4. Using FI as a holding code where a decision could have been made. FI is for apparent deficiencies that could not be fully identified inside the agreed inspection scope. If the inspector saw the defect, had access to it, and could have tested it, the observation must be coded C1, C2 or C3, not FI.

5. Applying more than one code to the same observation. Section 3.11 of Guidance Note 3 explicitly states “Only one classification code is to be recorded against each observation.” Splitting a single observation across C2 and C3 or annotating “C2/C3” is not compliant with the guidance.

6. Coding absence of an SPD as C1 or C2. Regulation 443 governs protection against transient overvoltage. Absence of an SPD where the risk assessment indicates one should be fitted is typically a C3 on an existing installation. It is not a C1, and it is not usually a C2 in a domestic dwelling.

7. Coding deteriorated earthing as a generic C2. A non-earthed installation is C2 per Table 3.5. But a badly corroded main earthing conductor, an undersized earthing conductor compared to Table 54.7, or a detached main bonding conductor each need their own individual observation and code – not one combined “earthing issues – C2” line.

8. Marking a report Satisfactory with C1, C2 or FI present. This is the single mistake most likely to expose the inspector to professional liability. Any C1, C2 or FI forces an Unsatisfactory overall outcome under Section 3.11 of Guidance Note 3. The overall Summary box on the EICR model form must reflect this.

Every coded observation should reference the BS 7671 regulation against which the defect is being scored. Citing the regulation provides justification for the code, supports the inspector in the event of a dispute, and gives the remedial contractor a clear brief for the corrective work. Examples of good observation wording:

• “Measured Zs at socket-outlet on ring final circuit exceeds the Table 41.3 maximum for the 32 A Type B device protecting the circuit – contrary to Regulation 411.4.5. Code C2.”
• “Absence of 30 mA RCD additional protection on lighting final circuit in dwelling, contrary to Regulation 411.3.4. Circuit otherwise tests as normal. Code C3.”
• “Main earthing conductor sized at 10 mm2 copper against line conductor of 25 mm2 copper – does not comply with Regulation 543.1.1 Table 54.7. Code C2.”
• “Insulation resistance between line and earth at DB1 Way 4 measured at 0.35 MOhm, below the 1.0 MOhm minimum in Table 64 of BS 7671 per Regulation 643.3. Code C2.”

The model EICR in Appendix 6 of BS 7671 has a dedicated Observations section (sometimes labelled Section K). Each line entry must carry exactly one classification code. Per Regulation 653.2, the report itself must include details of those parts of the installation inspected and tested, any limitations, any damage, deterioration, defects or dangerous conditions, any non-compliance with BS 7671 which may give rise to danger, the inspection schedule, and the schedules of circuit details and test results from Section 643.

Regulation 653.4 additionally requires the report to state a recommended interval until the next inspection, with an explanation for the recommendation. That interval depends on the type of installation, the frequency of use, the quality of maintenance and external influences – Regulation 652.1 does not prescribe fixed intervals in years. Specific recommended intervals are given in IET Guidance Note 3 Tables 3.1 and 3.2 for different installation types. The statutory 5-year maximum for domestic installations in the private rented sector in England is set by the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020, not by BS 7671 itself.

For the full technical reference on how insulation resistance is tested under Regulation 643.3 and Table 64, see our guide to insulation resistance testing under BS 7671.

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