4.3 Code C3 (Improvement Recommended) & Code FI (Further Investigation) Criteria

Code C3: Improvement Recommended

Technical Definition & Application

Code C3 is defined under BS 7671 and IET Guidance Note 3 as "Improvement Recommended". It is assigned to observations where an item does not comply with the current technical requirements of BS 7671 (BS 7671:2018+A2:2022), but where the non-compliance does not present an immediate danger (C1) nor a potential danger (C2).

Assigning Code C3 informs the duty holder or client that while the installation is safe for continued service in its present state, upgrading the identified items would enhance the overall level of safety of the installation to align with modern best practices.

Crucial Rule for EICR Outcomes: An EICR that contains multiple Code C3 observations—and zero C1, C2, or FI codes—results in an overall condition assessment of SATISFACTORY. Code C3 items do not render an EICR Unsatisfactory.

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Common Code C3 Examples (per BPG4 Issue 5)

1. Absence of RCD Protection on Socket-Outlets (Low-Risk Domestic/Commercial): Socket-outlets rated ≤ 32A in a dry indoor domestic environment installed under earlier editions of BS 7671 that lack 30mA RCD protection, provided the socket-outlets are unlikely to supply equipment outdoors, basic/fault protection (ADS and earthing) is intact, and Zs is fully compliant.
2. Absence of RCD Protection for Cables Buried in Walls: Cables concealed in walls at a depth of less than 50mm without earthed metallic mechanical protection (violating Reg 522.6.202 for modern installations), provided the circuit has compliant ADS, intact CPC, and no history of damage.
3. Absence of Surge Protection Devices (SPD): Installation lacking Surge Protection Devices required under BS 7671:2018+A2:2022 Regulation 443.4, where a risk assessment has not been conducted, but no direct equipment failure or hazard is evident.
4. Absence of Arc Fault Detection Devices (AFDD): Lack of AFDDs on socket-outlet circuits in Higher-Risk Residential Buildings (HRRBs), Houses in Multiple Occupation (HMOs), or boarding schools under Regulation 421.1.7.
5. Missing Safety & Warning Notices:
   • Missing "Periodic Inspection & Testing" warning notice on main distribution boards (Reg 514.12.1).
   • Missing "Harmonised Cable Colours" warning label where pre-2004 (red/black) and post-2004 (brown/blue) wiring exist together (Reg 514.14.1).
   • Missing "RCD Quarterly Test" instruction label adjacent to RCDs (Reg 514.12.2).
   • Missing "Dual Supply / Alternative Source of Supply" warning labels where microgeneration (solar PV/battery storage) is installed (Reg 514.15.1).
6. Inadequate Support Against Premature Collapse: Wiring systems supported by plastic cable trunking or plastic clips above escape routes without metallic fixings (violating Reg 521.10.201), where the route is not a primary designated high-density fire escape corridor requiring C2.
7. Metallic Switch Plates Connected to Earth without Terminal Identification: Metal light switches correctly connected to a continuous CPC, but where the CPC conductor is not encased in green/yellow sleeving inside the backbox.

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Code FI: Further Investigation Required Without Delay

Technical Definition & Critical Risk Rationale

Code FI is assigned when an inspection or test reveals an apparent defect, anomaly, or unverified safety condition that cannot be fully evaluated or declared safe during the periodic inspection without further investigation, specialized equipment, or intrusive access.

Under IET Guidance Note 3 and BPG4, if an inspector cannot verify whether a circuit or component is safe, safety cannot be assumed. Therefore, the presence of a single Code FI observation automatically results in an overall EICR assessment outcome of UNSATISFACTORY.

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Common Triggers for Code FI

1. Unidentified / Unverified Circuits: Circuits connected to a distribution board that cannot be traced to their final point of utilization or loads, where live test results indicate abnormal impedance or potential cross-connections.
2. Unverified Earth Fault Loop Impedance (Zs) on Sub-Mains: A sub-main feeding a remote distribution board or outbuilding where the protective device ratings, cable size, or upstream Zs cannot be determined or accessed due to locked plant rooms or sealed enclosures.
3. Ring Final Circuit Anomalies Unresolvable On-Site: Interconnected ring final circuits, cross-connected neutrals between different ring circuits, or broken ring continuity where the location of the fault or bridge cannot be determined within the agreed scope of inspection.
4. Mixed Supply Origins / Shared Neutral Connections: Unexpected voltages detected on neutral conductors during dead testing, suggesting shared neutrals or unisolated secondary supplies that require systematic tracing.
5. Evidence of Unauthorised Alterations / Hidden Junction Boxes: Indications of non-standard concealed cabling, high resistance readings, or thermal imaging anomalies inside ceiling voids or under floorboards that require lifting floor coverings or intrusive builder work outside the standard inspection scope.

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Operational Limitations vs Code FI

It is vital for C&G 2391-51 candidates to distinguish between an Agreed Operational Limitation and a Code FI observation:

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Decision Logic for EICR Coding & Overall Outcome

When completing an EICR, the inspector must apply a rigorous decision matrix to arrive at the final overall assessment:

• If direct danger is present (live conductors exposed) -> Code C1 -> Outcome: UNSATISFACTORY
• If potential danger is present (single fault could cause danger) -> Code C2 -> Outcome: UNSATISFACTORY
• If safety cannot be verified on site -> Code FI -> Outcome: UNSATISFACTORY
• If non-compliance exists but presents no immediate or potential danger -> Code C3 -> Outcome: SATISFACTORY

Reporting Best Practices for 2391-51 Examinations

• Never combine multiple defects into one observation code: Each distinct defect must be listed individually with its specific location.
• Reference Regulation Numbers: Cite the specific BS 7671 regulation (e.g., Reg 514.12.1 for missing labels).
• Clear Actionable Recommendations: State what corrective action is needed (e.g., "Fit missing RCD test notification label to DB-1").