Comprehensive RCD Risk Assessment Matrix for EICR Coding

During an Electrical Installation Condition Report (EICR), assessing the absence, failure, or incorrect specification of a Residual Current Device (RCD) requires a documented, risk-based approach. The environment directly dictates the severity of the defect. What constitutes a Code C3 in a controlled commercial office may escalate to a Code C2 in a school or public hotel lobby.

Colour-Coded Defect Mapping

To provide instant visual clarity during reporting, our diagnostic matrix maps directly to standard industry severity protocols:

• Code C1 (Red): Danger present. Risk of injury. Immediate remedial action required.
• Code C2 (Orange): Potentially dangerous. Urgent remedial action required.
• Code C3 (Green): Improvement recommended.
• FI (Yellow): Further Investigation required without delay.

Regulation 411.3.3: Risk Assessment for the Omission of an RCD

Regulation 411.3.3 mandates 30 mA RCD protection for all socket-outlets (≤ 32 A). An exception to omit RCD protection is permitted only if a formally documented risk assessment determines that the RCD protection is not necessary. This exception is bound by strict BS 7671 definitions based on user competence (BA classifications):

• BA1 (Ordinary Persons): People who are neither electrically skilled nor instructed (e.g., in domestic homes, offices, retail shops, hotel public areas). Risk assessments are completely invalid for omitting RCDs. Code C2.
• BA2 (Children): Persons requiring specific safety considerations due to age. Risk assessments are completely invalid. Code C2.
• BA3 (Disabled Persons): Individuals not in full command of their physical or intellectual abilities. Safety considerations override historical compliance. Code C2.
• BA4 (Instructed) & BA5 (Skilled Persons): Persons sufficiently trained or supervised (e.g., in factories, testing labs, server rooms). A documented risk assessment is permitted to omit a 30mA RCD. If a valid assessment exists, it is compliant (No Code). If it is missing, it is coded as a Code FI (Further Investigation) under 411.3.3(b) to prompt the creation of the document or retrofit.
• Outdoor Mobile Equipment: Regardless of BA classification, if the socket-outlet can reasonably supply mobile equipment used outdoors, the exception is permanently voided. Code C2.

TT Earthing Systems & Mandatory RCD Fault Protection

Under BS 7671, RCDs are completely mandatory for fault protection in TT earthing systems. Because the earth fault loop impedance (Zs) relies on a local earth electrode, standard overcurrent protective devices (MCBs/Fuses) will not draw enough fault current to achieve automatic disconnection. Conversely, standard TN systems (TN-S/TN-C-S) possess low Ze values and do not strictly require a main RCD at the origin.

The Danger of Type AC RCDs and DC "Blinding"

A critical update in BS 7671 concerns the blinding of Type AC RCDs. Type AC units are designed only to detect pure alternating current faults. Modern commercial environments are saturated with equipment that utilises internal rectifiers, variable speed drives, and switch-mode power supplies. These devices inject smooth or pulsating DC leakage currents back into the installation.

This DC leakage saturates the magnetic core of a Type AC RCD, effectively "blinding" it. It will fail to trip during a lethal AC shock. If a Type AC RCD is found supplying these DC-producing loads, it is an immediate Code C2 (Regulation 411.3.2.1). The installation must be upgraded to Type A or Type B devices.

Tester's Field Guide: Identifying DC Leakage Sources

📊 Summary Reference Table for Inspectors