How to check your main bonding conductors

Helpful video reference. The GSH Electrical Training tutorial "How to Test the Protective Bonding Conductor — Testing and Fault Finding Hints and Tips" is the video reference here. GSH Electrical Training produces UK-specific electrical training content for City and Guilds and EAL qualifications, covering BS 7671 requirements. The testing procedure shown is what an electrician would carry out during an EICR or a test on newly installed bonding.

1. What main protective bonding is, and why it matters

Every property with a gas or water supply that enters through metal pipes must have those pipes bonded to the main earth terminal at the consumer unit. This is a BS 7671 requirement under Regulation 411.3.1.

The reason is simple. If a fault somewhere in the electrical installation puts a live voltage onto a metallic water or gas pipe, anyone touching that pipe and a separately earthed surface at the same time could receive a dangerous shock. The bonding conductor creates a low-resistance path between the pipe and earth, so the fault current flows to earth rather than through a person, and the protective device (fuse or circuit breaker) can operate quickly.

It does not matter that you have RCD protection throughout the property. The bonding conductors are a separate and additional safeguard.

2. What to look for at the gas meter

Find your gas meter, which is usually outside near the front of the house or in a utility cupboard. Look for a green and yellow cable, at least 10mm2, clamped to the gas pipe within about 600mm of where the pipe enters the building on the consumer's side. The clamp will look like a metal bracket with a screw fixing, and it may carry a warning label saying something like "Safety Bonding — Do Not Remove."

Check:

• The clamp is on bare metal pipe, not on paint, plastic coating or lagging
• The clamp screw is tight and the conductor is not loose
• The cable enters the building and runs continuously to the consumer unit
• There are no obvious signs of corrosion at the clamp

3. What to look for at the water supply

Find where the cold water supply enters the building from the street. In most east Kent properties this is a 15mm or 22mm copper pipe appearing through the floor or wall near the kitchen or utility. Look for a green and yellow cable clamped to the metal pipe near that entry point.

The same checks apply as for the gas pipe: bare metal contact, tight fixing, no corrosion, continuous cable run. If the incoming service is entirely in plastic pipe from the street, bonding may not be required for that service — but a qualified electrician should confirm this.

4. Follow the conductors to the consumer unit

Trace both bonding cables from the service pipes to the consumer unit. In well-installed properties they run in the shortest practical route, usually clipped to the surface or run in conduit. They should terminate at the main earth terminal bar inside the consumer unit enclosure.

Look for:

• Continuous cable runs with no joins or interruptions
• No damage to the cable insulation along the run
• A secure termination at the consumer unit — no loose strands

Do not open the consumer unit to check this. An electrician will check the internal terminations during an EICR.

5. What an electrician checks further

Beyond the visual inspection, a qualified electrician will use a low-resistance ohmmeter to measure the continuity of each bonding conductor. The reading should be very close to zero ohms. A high reading, or an open circuit, indicates a break somewhere in the conductor or a loose connection at one of the terminations.

This is one of the standard checks on every EICR. It cannot be done safely without the correct test equipment and training.

When to call us

If your main bonding conductors are missing or in poor condition, fitting new ones is a straightforward job for a qualified electrician. It is usually done in a single visit and can be combined with an EICR if you want the full picture on your installation. Richard covers east Kent and quotes a fixed price before any work starts.