2.3 Sample Expansion & Defect Escalation Criteria

A fundamental principle of Periodic Inspection under IET Guidance Note 3 (Section 3.8.3) is that sampling is dynamic, not fixed. The initial sampling percentage agreed in Section D of the EICR represents only a baseline starting point. If non-compliances, physical damage, or unexpected degradation are uncovered within that initial sample, the inspector is mandated to execute a sample expansion strategy.

Dynamic Sampling & Escalation Triggers

The inspector cannot ignore defects found in a 10% sample and simply write up the report. If 10% of an installation exhibits defects, it is statistically probable that similar defects exist across the uninspected 90%.

Escalation Triggers (GN3 Section 3.8.3)

Sample expansion is automatically triggered when any of the following conditions are encountered:

1. Physical Damage or Severe Degradation: Cracking, broken enclosures, water ingress, or mechanical impact damage.
2. Thermal Overheating & Arcing: Discoloured insulation, charred terminal blocks, or melted switch components.
3. Widespread Wiring Non-Compliances: Missing CPC sleeving, un-earthed metal fittings, incorrect conductor identification, or loose terminations.
4. Incorrect Protective Device Coordination: Wrong MCB types, oversized fuses, or missing mandatory 30 mA RCD protection on socket circuits.
5. Inaccurate Circuit Schedules: Severe discrepancies between distribution board charts and actual circuit wiring layout.

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Isolated vs. Systemic Defects

When a defect is identified, the inspector must categorize it as either an isolated defect or a systemic installation issue to determine the appropriate escalation response.

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Step-Wise Sample Escalation Protocol

The escalation protocol follows a clear engineering sequence:

Phase 1: Identification & Preliminary Assignment

• Identify the non-compliance within the initial sample.
• Assign an initial EICR Classification Code (C1, C2, C3, or FI).

Phase 2: Targeted Local Expansion (Phase 1 Escalation)

• Increase the sample size from the baseline (e.g., 10%) up to 25% or 50% within the same circuit class or distribution board.
• Inspect adjacent accessories and circuits to determine whether the issue is isolated.

Phase 3: Total Circuit Class Expansion (Phase 2 Escalation)

• If additional non-compliances are identified during Phase 2, escalate the sample to 100% inspection and testing of that entire circuit type (e.g., 100% of all lighting circuits or 100% of all socket outlets supplied by that DB).

Phase 4: Client Consultation & Contract Scope Variation

• If 100% expansion across the distribution board uncovers multi-board failures, the inspector must formally halt work, contact the client, explain the systemic safety risk, and request written authorization for a full installation scope expansion (additional billable hours/access).

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Mandatory Protocol for Code C1 (Danger Present)

A Code C1 classification represents an immediate threat to life or property. Examples include exposed live conductors accessible to touch, live metalwork due to a fault, or an un-earthed installation with a line-to-earth short circuit.

The inspector's duties upon discovering a Code C1 defect are strict and non-negotiable:

1. Immediate Verbal Notification: Verbally inform the client or duty holder immediately on site.
2. Make Safe / Isolation: Seek client permission to immediately isolate the dangerous circuit or equipment. If permission is granted, isolate, lock off, and tag out the circuit.
3. Written Dangerous Condition Notification: Issue a formal Dangerous Condition Notification (or Danger Notice) in writing to the person ordering the work before leaving the premises.
4. Warning Labelling: Apply prominent yellow warning labels to the isolated distribution board or equipment.
5. EICR Classification: Record the defect under Section F of the report. The overall assessment of the installation MUST be declared Unsatisfactory.

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The Role of Classification Code FI (Further Investigation)

Code FI (Further Investigation Required) is assigned when an observation indicates potential danger, but the true extent of the hazard cannot be fully determined without further invasive investigation or specialized access.

Triggers for Code FI

• Abnormally high Earth Fault Loop Impedance ($Z_s$) readings on concealed sub-main cables where the protective route cannot be traced visually.
• Unmapped, unlabeled distribution boards supplying locked or inaccessible areas.
• Evidence of thermal overheating or moisture ingress inside sealed ceiling voids or floor ducting that cannot be opened during standard inspection.

Impact of Code FI on EICR Assessment

Under BS 7671, if ANY observation is assigned a Code C1, Code C2, or Code FI, the overall outcome of the EICR MUST be marked as UNSATISFACTORY. An installation cannot be reported as Satisfactory if uninvestigated potential hazards remain.

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Managing Client Refusal of Sample Expansion

In some commercial or domestic situations, a client may refuse to authorise sample expansion due to cost constraints, fear of disruption, or operational requirements.

When a client refuses necessary sample expansion required by GN3:

1. Do Not Force Access / Overrule: The inspector cannot force access or overrule client refusal.
2. Document Formal Limitation: Record the client's explicit refusal as a formal Operational Limitation in Section D of the EICR (e.g., "Sample expansion to 100% of lighting circuits refused by client following discovery of un-earthed metal luminaires").
3. Highlight Unverified Risks: Clearly state in Section E (Summary of the Installation) that uninspected circuits pose unverified safety risks.
4. Issue Unsatisfactory Report: Issue an Unsatisfactory EICR based on the defects already uncovered in the initial sample.

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Summary of EICR Classification Codes & Action Triggers