7.3 EICR Classification Coding: Code C3 & Code FI
Key Takeaways
C3 means Improvement recommended: an identified safety improvement is recommended without present or potential danger. A harmless difference from the latest edition does not automatically require C3, and historical compliance is not a prerequisite for the code.
Under BS 7671:2018+A4:2026, Code FI has been redefined as 'further investigation is advised' and decoupled from Codes C1/C2: an FI observation does NOT result in an Unsatisfactory EICR outcome.
An EICR with no C1 or C2 observations is assessed 'Satisfactory', even when it contains multiple C3 and FI observations. Give the client clear improvement and investigation advice.
Do not use FI instead of classifying an established deficiency. BPG 4 gives C2 for insulation resistance below 1 MΩ between linked live conductors and Earth; missing circuit identification is also a known observation rather than, by itself, an unexplained anomaly.
An A4 technically Satisfactory EICR does not remove England landlord duties. Where Regulation 3(4) applies, required investigative or remedial work must be completed within 28 days of inspection or the shorter report period, with the required written confirmation.
7.3 EICR Classification Coding: Code C3 & Code FI
Core Regulatory Benchmark: The classification codes on an Electrical Installation Condition Report serve distinct technical functions under BS 7671:2018+A4:2026 Regulation 653.2: Code C3 ('Improvement recommended') identifies a recommended safety improvement where there is no immediate or potential danger, while Code FI ('Further investigation is advised') addresses hidden anomalies where safety cannot be confirmed within the agreed inspection scope.
CRITICAL REGULATORY OVERHAUL UNDER BS 7671:2018+A4:2026: Under BS 7671:2018+A4:2026 and official IET guidance (IET Guidance Note 3 and IET Wiring Matters, July 2026, Michael Peace CEng MIET), Code FI has been completely decoupled from Codes C1 and C2. Code FI does NOT make an EICR Unsatisfactory! An EICR containing only Code C3 and/or Code FI observations produces an overall condition assessment of SATISFACTORY (accompanied by advisory notes for the client). Only Code C1 and Code C2 observations mandate an UNSATISFACTORY outcome.
Code C3: Improvement Recommended
BS 7671 Regulation 653.2 and Electrical Safety First Best Practice Guide 4 (BPG 4) define Code C3 as: 'Improvement recommended.'
Core Regulatory Principle: An Old Installation ≠ An Unsafe Installation
A cornerstone of electrotechnical condition reporting emphasized by the electrical safety bodies (NICEIC, NAPIT, ECA) and Electrical Safety First is that an existing electrical installation is not unsafe simply because it does not comply with the latest edition of BS 7671. Inspectors must never weaponize classification codes to force expensive, unnecessary replacements on clients where an existing installation remains entirely safe for continued service.
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| CODE C3 REGULATORY PRINCIPLE |
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| AN OLD INSTALLATION ≠ AN UNSAFE INSTALLATION! |
| - If an installation complied with the 15th, 16th, or 17th Edition when erected, |
| - And conductors, accessories, and protective devices remain undamaged and sound, |
| - And Automatic Disconnection of Supply (ADS) is fully achieved within permitted times, |
| -----> Assess the actual safety improvement: C3 is not automatic for every newer requirement. |
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Defining Characteristics of Code C3:
- No Immediate or Potential Danger: The condition does not expose occupants to immediate electric shock (C1) nor does it represent a compromised protective safeguard vulnerable to a single fault (C2).
- Assess the Existing Condition: Consider its safety in use, design, installation history and current condition. Historical compliance does not itself determine the code.
- Safety Improvement: Recommend a meaningful improvement in electrical safety. A harmless non-conformity for which no improvement is recommended need not become a C3 observation.
- Non-Aggregation Rule: Multiple Code C3 observations NEVER accumulate or combine to trigger an Unsatisfactory report! Even if an EICR records ten or twenty C3 observations, the overall condition remains SATISFACTORY.
Comprehensive Code C3 Real-World Scenarios
| Observed Condition | Relevant Modern Regulation | Why It Is Classified as Code C3 |
|---|---|---|
| No 30 mA RCD additional protection for indoor socket-outlets unlikely to supply outdoor equipment | Reg 411.3.3 | C3 where fault protection is effective and no other potentially dangerous condition applies, such as a socket in a bath/shower location. Assess the use and surroundings; normal operation alone does not prove safety. |
| Sound combustible consumer unit under a wooden staircase or in a sole escape route, without a non-combustible enclosure | Reg 421.1.201 | BPG 4 recommends C3 for this location-based improvement. A sound plastic unit elsewhere is not automatically C3 merely because it is plastic. Actual overheating, damage or accessible live parts require separate classification. |
| No bathroom supplementary bonding where omission conditions are verified | Reg 701.415.2 | If all ADS, 30 mA RCD and effective protective-bonding conditions permitting omission are met, absence is compliant and does not warrant C3 merely for lacking a historical bonding record. Missing bonding where required is C2. |
| Absence of SPD where the BPG 4 improvement criterion applies | Reg 443.4.1(a) and (c) | Current BPG 4 gives C3 where an SPD is required by these criteria. Absence in every existing dwelling is not automatically a coded observation; assess the applicable requirement and safety improvement. |
| Absence of AFDD in premises where the present requirement applies | Reg 421.1.7 | Current BPG 4 gives C3 for absence in high-rise residential buildings, HMOs, purpose-built student accommodation and care homes. Use the current premises and circuit scope, rather than treating absence everywhere as C3. |
| Missing required safety warning notice | Applicable identification/notices requirements | BPG 4 C3 examples include a missing alternative-supply warning or a required Safety Electrical Connection notice. Apply the actual notice requirement and any documentation exception; not every absent domestic notice is a deficiency. |
| Unidentified circuits at distribution board (missing or incomplete circuit chart) | Reg 514.8.1 / 514.9.1 | Unlabelled circuit breakers violate Regulation 514.8.1. This is a known, identified non-compliance classified as Code C3 (or C2 if switching off the wrong circuit creates operational hazard), NOT Code FI! |
Important
Apply the Plastic Consumer Unit Guidance Accurately
A sound combustible consumer unit without a non-combustible enclosure warrants C3 when under a wooden staircase or in the sole escape route. Plastic construction elsewhere, without a separate safety deficiency, is a non-conformity for which BPG 4 does not recommend a code solely on that basis.
Inspect the connections, condition and enclosure protection. An actual dangerous or potentially dangerous defect requires its own classification; neither the installation date nor the material alone determines C1 or C2.
Code FI: Further Investigation Is Advised (BS 7671:2018+A4:2026)
Under BS 7671:2018+A4:2026, the electrotechnical industry instituted a profound, long-awaited clarification to classification Code FI:
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| TERMINOLOGY EVOLUTION UNDER BS 7671 AMENDMENTS |
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| PRE-A4 (BS 7671:2018+A2:2022): 'Further investigation required without delay' |
| (Grouped with C1/C2 -> Mandated UNSATISFACTORY outcome) |
| |
| CURRENT (BS 7671:2018+A4:2026): 'Further investigation is advised' |
| (DECOUPLED from C1/C2 -> Results in SATISFACTORY outcome) |
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The A4 Reporting Change and Separate Statutory Duties
The IET’s July 2026 explanation separates investigation advice from an established dangerous or potentially dangerous condition. Under the current model form:
- FI wording: Further investigation is advised.
- Overall assessment: FI alone does not make the EICR Unsatisfactory. Only C1 or C2 has that effect.
- Clear advice: Identify the anomaly, explain why safety could not be determined within the agreed scope, and advise investigation as soon as possible.
- Legal follow-up: The report’s technical outcome does not cancel statutory duties. On 8 November 2026, England’s Regulation 3(4) still requires qualifying investigative or remedial work where its conditions are met, within 28 days of inspection or the shorter report period. The landlord must obtain written confirmation and provide it with the report to existing tenants and the local housing authority within 28 days of completion.
Do not infer that a technically Satisfactory report permits a landlord to ignore required investigation. Other jurisdictions and workplaces have their own applicable duties.
Strict Engineering Boundaries: What Code FI Is and What It Is NOT
The decoupling of Code FI reinforces its precise, narrow engineering purpose. Inspectors must adhere strictly to established engineering boundaries and must never use Code FI as a dumping ground for incomplete testing or demonstrable non-compliances:
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| PROPER ENGINEERING BOUNDARIES FOR CODE FI |
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| OBSERVED CONDITION | CORRECT CLASSIFICATION | WHY IT IS NOT CODE FI |
|------------------------------------+------------------------+-------------------------------------|
| IR below 1 MΩ between linked | CODE C2 | Known insulation deficiency; |
| live conductors and Earth | | locating it is a separate task. |
|------------------------------------+------------------------+-------------------------------------|
| Unidentified / unlabelled | CODE C3 (or C2) | Identified non-compliance with Reg |
| circuits at distribution board | | 514.8.1. Not an unverified anomaly. |
|------------------------------------+------------------------+-------------------------------------|
| Agreed inaccessible rooms, | EXTENT & LIMITATIONS | Operational agreed boundaries |
| locked voids, live server rooms | (Section D of EICR) | recorded before testing, not FI! |
|------------------------------------+------------------------+-------------------------------------|
| Suspected borrowed neutrals or | CODE FI | Genuine unverified anomaly where |
| unexplained cross-connections | | danger is suspected but cannot be |
| in inaccessible building fabric | | verified within agreed scope. |
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1. A Demonstrated Insulation Deficiency is Not FI
For the BPG 4 case of insulation resistance below 1 MΩ between live conductors linked together and Earth, use C2. For example, a valid result on that test establishes the deficiency. Check the test conditions and disconnected equipment before interpreting the result.
- This is an identified insulation problem, not simply uncertainty over concealed wiring.
- Do not offer C3 solely because the installation is old or no active shock is observed.
- Locating the damaged cable or connection is fault finding; agree that work separately as appropriate. Not knowing its exact physical location does not turn the established deficiency into FI.
2. Unidentified Circuits are NOT Code FI!
Distribution boards containing unlabelled circuit breakers or fuses violate Regulation 514.8.1.
- This is an identified departure from the standard.
- The inspector must assign Code C3 (Improvement Recommended), or Code C2 if the inability to isolate a specific circuit presents an active hazard to critical plant or safety services.
- An inspector must not assign Code FI simply because circuit charts are missing.
3. Incomplete Inspection / Agreed Limitations are NOT Code FI!
Record agreed operational restrictions and areas not inspected in Section D (Extent and Limitations). Inaccessibility alone is not an FI observation. If evidence separately indicates a potentially unsafe anomaly whose safety cannot be determined within that scope, explain it and advise investigation; a limitation must not conceal an already established dangerous condition.
4. What ARE Legitimate Applications of Code FI?
Under BS 7671:2018+A4:2026 and current IET guidance, Code FI is reserved exclusively for situations where visible or measured evidence indicates that an unverified condition or concealed alteration may pose danger, but the agreed extent and limitations prevent the inspector from determining whether danger exists:
- Unverified Cross-Connection: An unexplained operating anomaly suggests a concealed interconnection, but inspection and testing have not established its existence or safety. Describe the evidence and necessary investigation. If testing has already proved a borrowed neutral, classify the demonstrated defect C2; an unknown physical route does not justify FI.
- Anomalous Earth Loop Readings Suggesting Concealed Generation / Supplies: Unexplained supply loop impedances or anomalous neutral-to-earth voltages suggesting the presence of an unverified secondary power source, unauthorized private generation, or an unverified secondary neutral-earth link in a sub-distribution network.
- Concealed Alterations of Dubious Integrity: Non-standard, amateurish cabling disappearing into structural building fabric where its termination, loading, or route cannot be determined without destructive opening of walls, and where the inspector has reason to suspect potential danger.
The EICR Master Decision Matrix & Mermaid Workflow
An EICR records an assessment of condition within its stated extent and limitations. Its technical outcome and any applicable statutory follow-up duties must both be communicated accurately.
Master EICR Classification Decision Matrix (BS 7671:2018+A4:2026)
| Classification Code | Meaning | Urgency Level | Inspector Action Required | Impact on Overall Assessment |
|---|---|---|---|---|
| Code C1 | Danger Present | Immediate | Notify the person ordering the work immediately and in writing; seek agreement to make safe; record outstanding danger and action. | UNSATISFACTORY |
| Code C2 | Potentially Dangerous | Urgent | Document defect in schedule of observations (Section K); formally advise duty holder that urgent remedial action is required. | UNSATISFACTORY |
| Code C3 | Improvement Recommended | Non-urgent | Record observation in Section K; explain modern safety benefits to client; installation remains safe for continued service. | SATISFACTORY |
| Code FI | Further Investigation Is Advised | Advise investigation as soon as possible | Detail the anomaly and investigation needed. Explain applicable statutory action, including England landlord duties where triggered. | SATISFACTORY if no C1/C2 |
Worked Practical Case Studies: Code C3 and Code FI
Case Study 1: Domestic Installation with Multiple C3 Observations
- Scenario: An EICR on a 1998 house finds a sound combustible consumer unit under a wooden staircase without a non-combustible enclosure; indoor sockets without 30 mA RCD additional protection; a missing required Safety Electrical Connection notice; and missing circuit identification. The socket circuit has effective ADS ( against the applicable limit), is unlikely to supply outdoor equipment and has no other potentially dangerous condition. No C1, C2 or FI is found.
- Analysis: Each specified condition meets a BPG 4 C3 improvement example: the consumer unit’s location, indoor socket additional protection, required safety notice and circuit identification. These codes follow the actual safety-improvement criteria, rather than the house’s age. The circuits’ fault protection remains effective.
- Outcome: Four Code C3 observations. Overall assessment in Section E: SATISFACTORY. Multiple C3 observations do not accumulate to make an installation unsatisfactory.
Case Study 2: Commercial Office with a Confirmed Neutral Interconnection
- Scenario: The first-floor RCD trips when second-floor lighting is operated. Following safe isolation of all relevant sources and disconnection of connected equipment and neutral-bar links, testing proves a concealed shared neutral between the separately protected circuits. The plastered ceiling route is outside the agreed opening-up scope.
- Analysis: The testing establishes a borrowed neutral and a back-feed hazard during future isolation. Finding the exact junction is subsequent fault finding; the hidden route does not leave the existence of the defect unverified.
- Outcome: Code C2, with an overall UNSATISFACTORY assessment. Explain the hazard, agree safe action affecting all interconnected circuits and advise urgent correction. Record the limitation and necessary fault-location work, rather than substituting FI for the demonstrated defect.
Case Study 3: Retail Shop with Excessive Earth Fault Loop Impedance
- Scenario: In a retail premises, testing a 32 A Type B MCB socket circuit without RCD yields a measured of (Table 41.3 maximum is ).
- Analysis: The nominal estimate is , within the Type B magnetic tolerance band and below the guaranteed operating current used for the given limit. The result fails the applicable protection criterion for 0.4 s. It does not establish a definite thermal-only trip time.
- Outcome: One Code C2 observation. Overall assessment in Section E: UNSATISFACTORY.
Case Study 4: Workshop with Sub-1.0 MΩ Insulation Resistance
- Scenario: With equipment appropriately disconnected, a valid test on a 230 V workshop radial gives between line and neutral linked together and Earth. This is below the Table 64 minimum of . The client asks for FI so their maintenance team can locate the problem later.
- Analysis: The specified linked-live-to-Earth result establishes the BPG 4 C2 insulation deficiency. The inspector can classify it without knowing the fault’s exact location. Agree subsequent fault finding and correction separately; do not use FI or C3 to soften this established result.
- Outcome: One Code C2 observation (NOT Code FI!). Overall assessment in Section E: UNSATISFACTORY.
An EICR finds an undamaged combustible consumer unit with sound connections in a cupboard under a wooden staircase, without a non-combustible enclosure. What classification does current Electrical Safety First BPG 4 recommend for this location-based observation?
Code C1 (Danger Present), because plastic switchgear violates current Building Regulations.
Code C3 (Improvement Recommended), because this sound combustible unit is under a wooden staircase without a non-combustible enclosure.
Code C2 (Potentially Dangerous), because all plastic consumer units require urgent replacement with metal enclosures under Regulation 421.1.201.
Code FI (Further Investigation Is Advised), requiring destructive laboratory fire testing of the plastic casing.
Under BS 7671:2018+A4:2026 and current IET guidance, what is the official definition of Code FI, and how does it impact the overall assessment of an EICR?
'Further investigation is advised'; FI alone does not make the report Unsatisfactory. The overall assessment is Satisfactory if no C1 or C2 is present, with clear investigation advice.
'Further investigation required without delay'; any single FI observation automatically mandates an overall 'Unsatisfactory' assessment.
'Further investigation is mandatory'; it is assigned only when insulation resistance falls below 1.0 MΩ and mandates an 'Unsatisfactory' assessment.
'Fault identified'; it automatically escalates to a Code C1 if remedial action is not completed within 28 days.
An A4 EICR records five properly justified C3 observations and one FI observation concerning an unexplained concealed-circuit anomaly. No C1 or C2 is identified. What is the report’s overall technical assessment?
Satisfactory, because Code C3 and Code FI are decoupled from C1 and C2 and do not mandate an unsatisfactory outcome.
Unsatisfactory, because any single Code FI observation automatically renders the entire EICR unsatisfactory.
Unsatisfactory, because five or more Code C3 observations aggregate to create an unsatisfactory condition.
Invalid, because Code FI cannot be recorded on an EICR that contains Code C3 observations.
During periodic testing of a 230 V commercial radial with equipment appropriately disconnected, a valid insulation-resistance test between line and neutral linked together and Earth gives 0.35 MΩ, below the 1 MΩ minimum. The client asks for FI until the fault can be located. What classification follows current BPG 4?
Code C2: the linked-live-to-Earth result establishes an insulation deficiency; not knowing its exact physical location does not justify FI.
Assign Code FI, because the inspector does not know the exact physical location or room where the cable insulation has failed.
Assign Code FI, because any measured reading that fails BS 7671 limits must be investigated before a classification code can be chosen.
Assign Code C1 immediately, because any insulation resistance reading below 1.0 MΩ represents an active danger of electrocution.
Sections you finish are checked off in the contents.