EICR: No Main Protective Bonding — The Classic C2

BS 7671 Regulation 411.3.1.1 requires main protective bonding to be applied to extraneous-conductive-parts as part of the Automatic Disconnection of Supply (ADS) protective measure. The bonding ensures that, under a fault condition that places a potential on the installation's exposed metalwork, the metallic services entering the dwelling are also raised to (approximately) the same potential — preventing dangerous touch-voltage differences across the building.

Verifying main protective bonding during EICR is a methodical walk-through of the service entry points:

1. Locate the Main Earthing Terminal (MET) — typically at or near the consumer unit, sometimes in the meter cupboard or a separate earth block.
2. Identify each metallic service entering the dwelling: gas meter (within 600 mm of the meter), water service (typically at the rising main / stop tap), oil tank supply (if applicable).
3. Trace each bonding conductor from the MET to the service pipe. The conductor must be visible / continuous (no joints unless in an accessible enclosure with the joint protected).
4. Verify the bonding clamp at the service — BS 951-compliant clamp with a permanent "Safety Electrical Connection — Do Not Remove" label.
5. Verify the bonding conductor CSA against Table 54.8 for the supply earthing arrangement.
6. Test continuity between the MET and the bonded service (typically R₂ method): a low-resistance reading (< 0.05 Ω is typical for a sound installation).

BS 7671 / IET GN3 give a strict hierarchy for observation coding (see the dedicated EICR Code C1, C2, C3 and FI guides). Missing main bonding is almost always C2 because:

The single exception: where the structure has NO extraneous-conductive-parts (e.g., all-plastic plumbing from the boundary, no gas service, no metallic structural steel) — but the inspector MUST verify this and document the rationale on the EICR.

Main bonding conductor CSA depends on the earthing arrangement:

The remedial action for missing main bonding is straightforward: install the missing conductor(s). The specifics:

1. Confirm the supply earthing arrangement (PME, PNB, TN-S, TT) — this dictates the bonding conductor CSA.
2. Select the conductor — 10 mm² 6491X green-and-yellow for most PME domestic; 6 mm² for non-PME where appropriate; or larger per Table 54.8.
3. Route the conductor from the Main Earthing Terminal at the consumer unit to the service pipe, by the shortest practicable route, protected against mechanical damage.
4. Terminate at the MET with the existing earthing arrangement (typically a brass terminal bar).
5. Terminate at the service with a BS 951 clamp, applied to bare metal pipe within 600 mm of the meter or first point of entry into the building. Apply the clamp to a continuous run of metallic pipe — never to a section that has a plastic insert downstream.
6. Affix the BS 951 "Safety Electrical Connection — Do Not Remove" label adjacent to each clamp.
7. Test continuity between the MET and the bonded service — should read sub-ohm.
8. Issue an EIC or MEIWC for the remedial work; provide a copy to the responsible person (and, for rented properties under PRS Regs 2020, to the tenant within 28 days).