Main protective bonding at the meter

The main protective bonding conductor is part of the electrical installation, but it connects to the gas pipework. So a gas engineer needs to know where it should be, how to spot when it's missing or wrong, and what to tell the customer.

Where the connection goes

BS 6891 and BS 7671 agree. The bonding connection is made to the customer's fixed, rigid pipework on the outlet of the meter installation:

1. as near as practicable to where the pipe enters the premises
2. before any branch in the pipework
3. where it's accessible and can be inspected, with a warning label reading "Safety electrical connection – Do not remove"
4. with a connection that's mechanically and electrically sound and won't corrode.

It must not be connected directly to CSST, or to the pliable connector from the meter outlet.

Meters in outside boxes

Gas Safe Register's Technical Bulletin 102 says the preferred position is on the pipework where it enters the property. Where that isn't practicable, because the pipe enters the building out of sight, the bond may be made inside the meter box, on the meter outlet pipe before any branch or tee. The cable mustn't damage the box or the seal of any sleeve. How it may leave the box depends on the supply pressure:

• Low pressure supply, built-in box: the cable leaves through the purpose-made rear sleeve (spigot) or the bottom exit, never through a hole drilled in the box. If it shares the rear sleeve with the gas pipe, seal the sleeve with non-setting, fire-resistant compound around both the pipe and the cable.
• Medium pressure supply: neither the pipework nor the bonding cable may go straight into the property from the box. Both must first come out of the box on the face of the building, then enter the property. The Unsafe Situations Procedure classes pipework or a bonding cable entering the property through the rear spigot of a medium pressure meter box as At Risk.

When bonding is missing or inadequate

You must tell the responsible person when equipotential bonding may be needed (GSIUR reg. 18(2)). Where you can't confirm the bonding is adequate, HSE's guidance is to tell them in writing. Leave a bonding notice. BS 6891 gives a typical example, which explains that:

• most electrical installations need main protective bonding of the gas and water pipes to the main earthing terminal, as BS 7671 requires
• the gas pipework in the property doesn't appear to have it
• the gas regulations require you to tell them it should be carried out by a competent person
• they should have it checked by a competent electrician, and if they're a tenant, tell the owner or agent.

When you install new pipework, fit any bonding needed yourself at the time if you're competent to do so. When a meter is moved, existing bonding may be fine as it is or may need altering. Any alteration is for an electrically competent person, and should be inspected and tested to BS 7671.

Sources: GSIUR 1998 reg. 18(2)duty to inform BS 6891:2015 8.4.3, Figures 8–9position, label, cable, notice BS 7671:2018 544.1.2 (via TB 102)bonding connection Gas Safe Register TB 102 (2018)meter boxes IGEM/G/11 Ed. 2 3.3.2notice in writing IGEM/G/11 Ed. 2 Table 1situations 2.10, 3.19 CCN1 Issue 16 §5assessed

▸Tutor notes

• Show photos of bonding connections (on the meter outlet, on a branch, on a pliable connector, in a meter box, with no label) and ask which are correct and why.
• Ask learners to fill in a bonding notice for a property where the bond is missing.
• CCN1 §5 item 11 asks for the minimum cross-sectional area of the main bonding conductor: BS 6891 gives 10 mm². Check this against the current BS 7671 if your course quotes a different figure.