Why a temporary bond goes across a cut in metal gas pipe, the order of work, and how it differs from permanent main protective bonding.
Metal gas pipework can carry electrical current, or sit at a different electrical potential on each side of a cut. Breaking it without a bond can create a spark, enough to ignite gas, or expose you to a shock. A temporary continuity bond gives the current a path around the break.
Before disturbing the pipe or its bonding, assess electrical hazards as well as the gas work. Diverted current can remain on pipework even after the property’s electrical main switch is opened. A temporary link does not make an existing dangerous voltage or current safe; stop and obtain the appropriate competent assistance where a hazard is suspected.
Order of work
- Shut off the gas in the normal way. The temporary electrical link protects continuity across the planned cut; it does not make the pipe safe to open or remove any other gas-work precautions.
- Identify where you will break into the metal pipe.
- Before cutting, clamp a temporary continuity bond across the section to be cut, with a clean metal-to-metal connection on each side.
- Check both clamps are tight on clean metal, so the bond actually carries current around the break.
- Do the gas work with the bond left in place while the pipe is open.
- Remake the joint and confirm the pipe is electrically and mechanically continuous again.
- Only then remove the bond, and carry on with tightness testing and recommissioning.
Temporary bond versus main protective bonding
- The temporary bond covers the duration of the work only. It is not a substitute for the installation's permanent main protective bonding.
- Permanent bonding: where metal gas pipework is an extraneous-conductive-part, its bonding conductor connects it to the installation's main earthing terminal. This limits the voltage difference someone could touch between the pipe and other bonded metalwork.
- A fault can still leave dangerous voltage on metalwork. Main bonding cannot stand in for an appliance circuit's protective conductor, and gas pipework must never serve as an earth electrode.
- Where bonding is required, secure the clamp to sound bare metal of the consumer's pipework after the meter or insulating section, before branches and as near the service entry as practicable. An electrically competent person should check the applicable BS 7671 position requirements.