7.2 EICR Classification Coding: Code C2 (Potentially Dangerous)

7.2 EICR Classification Coding: Code C2 (Potentially Dangerous)

Core Regulatory Benchmark: BS 7671 Regulation 653.2 and Electrical Safety First Best Practice Guide 4 define Code C2 as: 'Potentially dangerous. Urgent remedial action required.' While not presenting an immediate risk of shock or fire at the instant of inspection, a Code C2 defect signifies that the installation's protective safeguards have been compromised, such that a single foreseeable fault will create imminent, severe danger.

In electrotechnical condition reporting under the EAL Level 3 Inspection and Testing qualification framework (specifically Unit QCRB/001 and Unit QCR/001), mastering the distinction between Code C1 and Code C2 is the single most critical evaluative skill. Misclassifying a C1 as a C2 leaves occupants exposed to active lethal hazards without immediate intervention, while over-coding a C3 as a C2 imposes unwarranted financial and legal burdens on the duty holder.

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The Concept of the Single Fault Condition

The bedrock engineering principle underlying Code C2 is the single-fault condition (failure of basic protection or failure of fault protection):

+---------------------------------------------------------------------------------------------------+
|                             THE CODE C2 SINGLE-FAULT THRESHOLD                                    |
+---------------------------------------------------------------------------------------------------+
|  NORMAL RESTING STATE (Undisturbed)      ----->  SINGLE FORESEEABLE EVENT / FAULT                 |
|  - Enclosure closed; basic insulation            - Insulation breaks down inside Class I metal    |
|    intact.                                         kettle, motor, or luminaire, OR                |
|  - No person actively shocked right now.         - DNO PEN conductor breaks on PME supply, OR     |
|  - NO IMMEDIATE DANGER.                          - Fire occurs in building corridor.              |
|                                                                                                   |
|                                                  CONSEQUENCE OF COMPROMISED SAFEGUARD:            |
|                                                  - Earth path absent -> Metalwork stays at 230 V  |
|                                                  - Zs too high -> Protective device fails to trip |
|                                                  - Plastic clips melt -> Cables collapse & trap   |
|                                                  - POTENTIALLY DANGEROUS -> CODE C2!              |
+---------------------------------------------------------------------------------------------------+

Under BS 7671 Chapter 41, safety against electric shock relies on the coordination of Basic Protection (preventing direct contact with live parts) and Fault Protection (preventing dangerous touch voltages on exposed conductive parts during an earth fault via Automatic Disconnection of Supply, ADS).

When fault protection is absent, severely impaired, or uncoordinated, the installation sits in a latent, primed state of hazard. The moment an everyday electrical appliance suffers internal insulation degradation, or a utility neutral is disrupted, the lack of fault protection transforms the latent condition into an active, lethal touch voltage ($U_t > 50\text{ V AC}$). Because single electrical insulation faults are normal, statistically predictable occurrences over the lifetime of an installation, compromised fault protection represents an unacceptable risk requiring urgent remedial action.

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Comprehensive Real-World Code C2 Defects

Inspectors must apply rigorous technical benchmarks when identifying Code C2 conditions across electrical infrastructure:

Code C2 Defect Classification Matrix

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Deep Dive: Earth Fault Loop Impedance ($Z_s$) & Disconnection Failure

One of the most frequent examination scenarios in EAL Level 3 testing involves the evaluation of measured $Z_s$ values against maximum permitted values in BS 7671 Tables 41.2, 41.3, and 41.4.

Temperature Correction and the Governing Protective Device

Chapter 41 loop limits must be compared with results on a consistent temperature basis. For cold conductors, Appendix 3 gives the simplified sufficient check:

$Z_{s(\text{measured})} \le 0.8 \times Z_{s(\text{max, BS 7671})}$

For a Type B 32 A circuit-breaker with a tabulated maximum of $1.37\ \Omega$, this gives $1.37\times0.8=1.096\ \Omega$. Do not apply the factor again to a reference value already adjusted for measurement temperature. Exceeding the simplified figure calls for assessment using the applicable temperature-adjusted limit and device data; it does not by itself prove that ADS fails. Identify the required time for the actual circuit and earthing arrangement.

• Without RCD fault protection: For the TN socket circuit considered here, the applicable maximum is $1.37\ \Omega$ and the required disconnection time is 0.4 s. A measured $Z_s=1.95\ \Omega$ already exceeds that limit. At nominal voltage: $I_f \approx \frac{230}{1.95}=117.9\text{ A}$ This is about $3.68I_n$, within the Type B magnetic tolerance band of $3$–$5I_n$. The device might trip magnetically, but the guaranteed operating current used for the tabulated limit is $5I_n=160\text{ A}$. The measurement does not establish the required protection; do not predict a definite thermal-only trip or a precise delay. With failure against the applicable protection criteria established, classify C2.
• With RCD fault protection: Regulation 411.4.204 permits Table 41.5 to be applied on TN systems. Its 30 mA value is $1667\ \Omega$, derived from the 50 V basis. A circuit is not C2 merely because it exceeds the MCB loop limit if effective RCD fault protection satisfies the governing requirements. Verify protective-conductor continuity, correct RCD selection and operation, and overcurrent/short-circuit protection; a high loop reading can still indicate a real connection defect.

HIGH MEASURED Zs
       |
       v
Check result, circuit, required time, device and temperature basis.
       |
       +--> Applicable overcurrent-device protection meets the time?
       |         Yes: no C2 solely for failing a simplified 0.8 screen.
       |
       +--> Effective RCD fault protection meets its requirements?
       |         Yes: assess continuity and other protection/connection defects.
       |
       +--> Required fault protection is not effective: C2, urgent action.

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Regulation 521.10.202: Premature Collapse in Fire

Introduced in the 18th Edition of BS 7671 and reinforced in BS 7671:2018+A4:2026, Regulation 521.10.202 states:

'Wiring systems shall be supported such that they will not be liable to premature collapse in the event of fire.'

This regulation applies across the entire installation, not merely designated escape routes. Historically, non-metallic cable clips, plastic wall plugs, and plastic mini-trunking were standard installation methods. In multiple tragic fire events (notably the Shirley Towers fire in Southampton and Harrow Court in Stevenage), firefighters navigating smoke-logged premises became entangled in fallen overhead electrical cables, leading to line-of-duty fatalities.

EICR Classification Criteria for Regulation 521.10.202:

• Code C2 (Potentially Dangerous): Cables clipped to surfaces, suspended above false ceilings, or running along corridors and doorways supported exclusively by plastic clips, plastic trunking, or plastic ties where falling cables would block escape routes or trap firefighters.
• Rectification: Provide sufficient fire-resistant retention with suitable clips, bands, ties or other supports and anchors for the substrate. Select spacing for cable weight, route, load and the support manufacturer’s instructions; there is no universal 300–400 mm fixing interval. Other supports may remain where adequate fire retention is provided.

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Impact on Overall EICR Assessment & Duty Holder Obligations

Like Code C1, the presence of one or more Code C2 observations automatically results in an overall 'UNSATISFACTORY' assessment on the Electrical Installation Condition Report.

Statutory Duties Depend on the Setting

An EICR outcome does not create one UK-wide 28-day repair rule. C1 needs immediate action and C2 urgent action appropriate to the danger. Workplace duty holders must comply with EAWR; the risk governs the response.

For a specified tenancy covered by England’s private and social rented-sector regulations, Regulation 3(4) applies where the report indicates an actual or potential breach of the electrical safety duty and requires investigative or remedial work. A qualified person must carry it out within 28 days of the inspection and testing, or the shorter period specified. This can include investigation despite an A4 technically satisfactory report. Obtain the qualified person’s written confirmation, and supply it with the original report to existing tenants and the local housing authority within 28 days of completion. An EIC or Minor Works certificate is appropriate where the work requires it; the statutory confirmation is not limited to those certificate types.

Comparison: Code C1 vs Code C2 Response Protocols

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Worked Practical Case Studies: Code C2 in Practice

Case Study 1: Missing Main Protective Bonding to Gas Service

• Scenario: An inspector performs an EICR on a PME domestic installation. The incoming metallic gas pipe is confirmed to be an extraneous-conductive-part, but no effective main protective bonding exists. The main earthing connection is sound. Bonding is required under Regulation 411.3.1.2.
• Analysis: Missing required bonding permits a dangerous potential difference between the extraneous pipe and electrical exposed-conductive-parts under fault conditions. Bonding limits that difference within the equipotential zone; it does not guarantee that PME-connected parts remain at true-earth potential during an open-PEN event. The observed missing safeguard creates potential danger rather than proving present danger.
• Classification: Code C2 (Potentially dangerous. Urgent remedial action required.)
• Procedure: Record C2 in Section K, identify the missing required bonding and advise urgent repair. Determine the conductor size from the applicable Regulation 544.1 requirements and, for PME, Table 54.8 and the distributor’s conditions, rather than assuming 10 mm² in every case. Declare the overall condition UNSATISFACTORY.

Case Study 2: Measured $Z_s$ Exceeding Maximum Limit Without RCD

• Scenario: During testing of a 32 A radial socket circuit wired in 4.0 mm² / 1.5 mm² PVC cable protected by a 32 A Type B MCB on a TN-S supply, measured $Z_s$ at the furthest socket is $1.95\ \Omega$. The maximum permitted $Z_s$ in BS 7671 Table 41.3 is $1.37\ \Omega$. The circuit has no RCD protection.
• Analysis: At nominal voltage the estimated current is $230/1.95=117.9\text{ A}$, below the $160\text{ A}$ guaranteed magnetic operating current used for the tabulated limit. Since this lies within the Type B tolerance band, a magnetic trip is possible, but protection within 0.4 s has not been established against the applicable limit. Do not assert a definite thermal delay from that calculation.
• Classification: Code C2 (Potentially dangerous. Urgent remedial action required.)
• Procedure: The inspector documents the defect as Code C2 on the EICR, explains that the required 0.4 s disconnection has not been established and fault protection needs correction, and issues an UNSATISFACTORY overall condition assessment.