BS 7671:2018+A2:2022 Testing Explained: Dead Tests, Live Tests & 30mA RCDs

What actually happens during an 18th Edition EICR? We walk through continuity (R1+R2), 500V DC insulation resistance, earth fault loop impedance (Zs), and RCD trip times.

Flexicomm Engineering Team Published 7 min read

A thorough Electrical Installation Condition Report (EICR) is far more than a visual glance at a consumer unit. Under BS 7671:2018+A2:2022 and IET Guidance Note 3, an engineer follows a strict sequence of dead and live electrical tests to verify that protective devices will disconnect a fault fast enough to prevent electric shock or fire.

Phase 1: Dead Testing (Power Safely Isolated)

Before any live measurements are taken, the installation is safely isolated and locked off so the engineer can verify the integrity of the conductors themselves.

  1. Continuity of Protective Conductors (R1+R2)
    Confirms that the circuit protective conductor (earth) is continuous from the consumer unit to the furthest point of every radial and ring final circuit, and establishes a baseline for earth fault loop impedance.
  2. Ring Final Circuit Continuity
    For 32A ring sockets, end-to-end resistance measurements (r1, rn, r2) are taken and cross-connected to detect broken rings, loose terminals, or interconnected spurs.
  3. Insulation Resistance (500V DC — Reg 643.3.3)
    A calibrated 500V DC test voltage is applied between live conductors and earth to confirm cable insulation has not degraded, melted, or suffered moisture ingress. For 230V domestic circuits, readings must be at least 1.0 MΩ (healthy modern cabling typically reads >200 MΩ).

Phase 2: Live Testing (Verifying Fault Disconnection)

Once dead tests confirm the installation is safe to energise, live verification begins:

  • External Earth Fault Loop Impedance (Ze) & Prospective Fault Current (Ipf) — Verifies the incoming supply earthing arrangement (TN-S, TN-C-S, or TT) and confirms the main protective devices can safely interrupt a short circuit.
  • Circuit Earth Fault Loop Impedance (Zs) — Ensures that if a live conductor touches earthed metalwork, enough fault current flows to trip the MCB or RCBO within the maximum permitted disconnection time (typically 0.4 seconds for socket circuits).
  • 30mA RCD / RCBO Trip Time Testing — Tests residual current devices at 1× IΔn (30mA) to verify they disconnect within 300ms (Type AC/A) and protect against fatal electric shock.

Why Accurate Readings Matter

Cheap “drive-by” certificates often omit dead testing or copy-paste generic Zs values. Proper calibrated instrument testing protects occupants, satisfies insurance underwriters, and ensures landlords hold a legally defensible safety record.