Why bonding matters
How metal gas pipework can become live and how bonding protects people.
This topic supports
- M07.1Explain why gas pipework needs main protective bonding and where the connection must be made.
Draft: this lesson hasn't yet been technically reviewed.
Metal gas pipework runs through a building alongside water pipes, central heating and electrical wiring. If an electrical fault makes any of that metalwork live, someone touching the gas pipe and another earthed object at the same time could get a shock. And when a gas pipe is cut or a meter removed, any current flowing in the pipe can make a spark right where gas may be escaping.
There are two kinds of bonding, and they deal with these two dangers.
Main protective bonding: against electric shock
The conductor connects the gas pipework to the electrical installation's main earthing terminal, as BS 7671 (the IET Wiring Regulations) requires. Water pipes, other pipework, central heating and exposed structural metalwork are bonded the same way. Connecting them all together creates a zone where differences in voltage between them are removed, so the risk of electric shock is kept as low as possible. A metal pipe with an insulating section where it enters the building doesn't need bonding.
It's permanent, and it's part of the electrical installation. Who fits it and where is covered in 7.2.
Temporary continuity bonding: against sparks
Stray currents can flow through gas pipework. If you break the pipe while current is flowing, the gap can spark, and that spark could ignite gas, or give you a shock. A bridges the gap so the electrical path stays unbroken while you work. See 7.3.
Your duties as a gas engineer
- Tell the customer when bonding may be needed. Anyone who connects installation pipework to a primary meter must, wherever equipotential bonding may be necessary, tell the responsible person that it should be carried out by a competent person (GSIUR reg. 18(2)). When you install new pipework, fit the bonding yourself at the time if you're competent to.
- Maintain continuity while you work. Wherever it's needed to prevent danger, use a suitable bond until the work is finished and permanent continuity is restored (GSIUR reg. 10).
- Check for stray voltage before you start. Before working on pipework, assess the risks, including stray electrical currents, and check for stray voltage on exposed metalwork in the work area (see 7.4).
Missing or inadequate bonding is treated as an electrical issue rather than an ID or AR gas situation. You leave a bonding notice, as 7.2 explains.
Interactive artefact
Temporary continuity bonding
What happens to stray or fault current when a pipe is cut, with and without a temporary bond.
Will demonstrate
- The current path through metal pipework
- What happens when the pipe is broken without a bond
- Fitting and removing the bond in the right order
Planned. This interactive will appear here when it's built.
Sources: GSIUR 1998 regs 10, 18(2)continuity, bonding duty L56 (2018) paras 160–161purpose of each bond BS 6891:2015 8.4.3.1 commentarypurpose of bonding BS 7671:2018 411.3.1.2 (via TB 102)what's bonded IGEM/G/11 Ed. 2 Table 1, 3.3.2situation 3.19 CCN1 Issue 16 §5assessed
Tutor notes
- Ask learners to explain, in a sentence each, the difference between main protective bonding and a temporary continuity bond, and which law requires each.
- Ask why a temporary bond is still needed when main bonding is already fitted. BS 6891 says to use one irrespective of any permanent bonding.
- CCN1 §5 lists reg. 10 and the minimum size of the main bonding conductor (items 11 and 14(i)); both are covered across 7.1–7.3.