Electrical Bonding Defects: The Most Overlooked EICR Failure and How to Fix It
Of all the reasons properties fail EICR inspections in Manchester, electrical bonding defects are the most misunderstood. Property owners hear about faulty wiring, missing RCD protection and outdated consumer units — but bonding rarely gets a mention until the EICR report arrives with C2 observations that need fixing within 28 days. Yet bonding defects are among the most common findings we see across Greater Manchester, and among the most dangerous to leave unresolved.
This guide explains what electrical bonding is, why it matters, what defects inspectors commonly find, and how remedial work brings your property into compliance.
What Is Electrical Bonding?
Electrical bonding connects exposed metalwork in a building — gas pipes, water pipes, oil pipes, structural steelwork, central heating systems, air conditioning units — to the electrical earthing system. The purpose is to ensure that if a fault occurs and metalwork becomes live, the fault current has a low-resistance path to earth, causing the protective device to disconnect the supply quickly.
Without bonding, a fault could energise a gas pipe or water pipe. Anyone touching that pipe would provide the path to earth through their body. With bonding in place, the fault current flows through the bonding conductor instead, tripping the protective device before anyone is harmed.
There are two types of bonding in a building's electrical installation.
Main Protective Bonding
Main bonding connects the incoming metallic services — gas pipe, water pipe, oil pipe, and any other metallic service entering the building — to the main earthing terminal. This is done near the point where each service enters the building, using bonding conductors of a specified minimum size (typically 10 mm² or 16 mm² copper, depending on the size of the supply).
Main bonding is a fundamental safety requirement. It ensures that all metalwork entering the building from outside is at the same electrical potential as the earthing system. Without it, a fault anywhere in the building or even in the external supply network could create a dangerous voltage between metalwork and earth.
Supplementary Protective Bonding
Supplementary bonding provides additional connections between exposed metalwork within specific rooms — most commonly bathrooms, kitchens and plant rooms. It connects metal pipes, radiators, baths, basins, taps and any other exposed metalwork to each other and to the circuit protective conductor.
The requirement for supplementary bonding depends on the installation's earthing and RCD protection arrangements. Under current regulations, supplementary bonding in bathrooms may not be required if the installation has adequate main bonding, all circuits in the bathroom are RCD-protected, and all earth fault loop impedance values are within specified limits. However, in many older Manchester properties, these conditions are not met, and supplementary bonding remains necessary.
Why Bonding Defects Are So Common
Several factors contribute to the high incidence of bonding defects in Manchester properties.
Age of Housing Stock
Greater Manchester has a large stock of Victorian, Edwardian and pre-war properties. Many were built before bonding was a regulatory requirement, and while subsequent electrical work may have added some bonding, it is often incomplete or does not meet current standards.
Plumbing and Gas Work Without Electrical Coordination
When a plumber replaces a section of metal pipe with plastic, the bonding conductor that was clamped to the old metal pipe is left disconnected — or worse, connected to a short section of metal pipe that is now electrically isolated from the rest of the system. Similarly, a new boiler installation may alter the gas pipework routing without the bonding being reinstated.
This is one of the most common causes of bonding failure. The bonding was correct when it was installed, but subsequent non-electrical work has broken the continuity without anyone noticing. The electrician who installed the bonding has no way of knowing that a plumber will later replace the pipe section it is clamped to.
Kitchen and Bathroom Renovations
A bathroom refit that replaces copper pipes with plastic push-fit fittings, or a kitchen renovation that moves the sink and dishwasher, can disrupt existing bonding arrangements. Unless the contractor carrying out the work understands the electrical implications — and many do not — the bonding is not reinstated.
Modifications to the Gas Supply
Meter repositioning, replacement of lead gas service pipes with plastic, or the installation of a new gas main can all affect main bonding. The bonding conductor must be connected to the metallic pipework on the building side of the meter — if the pipe between the meter and the building is now plastic, the bonding point may need to move.
General Wear and Deterioration
Bonding clamps corrode over time, especially in damp environments. Conductors can be damaged during building work, hidden behind plasterboard, or cut by someone who does not know what they are. Labels identifying bonding conductors fade or fall off, making it unclear which cables serve a bonding function.
What EICR Inspectors Check
During an EICR inspection, the electrician specifically examines bonding in several ways.
Visual Inspection
The inspector visually traces bonding conductors from the main earthing terminal to each incoming service — gas, water, oil — and checks that the connections are secure, the conductors are undamaged, the correct size of conductor has been used, and the bonding clamps are in good condition.
Continuity Testing
Using a low-resistance ohmmeter, the inspector measures the resistance of the bonding path between the main earthing terminal and each bonded service. The resistance should be very low — typically well under 0.05 ohms for a properly installed bonding conductor. Higher readings indicate a poor connection, damaged conductor or interrupted bonding path.
Assessment of Supplementary Bonding
In bathrooms and other locations where supplementary bonding is required, the inspector checks that all exposed metalwork is bonded together and that the bonding paths have acceptably low resistance.
Common EICR Findings Related to Bonding
The following are findings we regularly see on EICR reports for Manchester properties.
C2: Main Bonding to Gas/Water Missing or Disconnected
This is the most serious bonding defect and is classified as C2 (potentially dangerous). It means the incoming gas or water pipe has no bonding connection to the earthing system. If a fault occurred that energised these pipes, there would be no protection — anyone touching the pipe could receive a lethal electric shock.
Remedial work: Install main bonding conductor from the main earthing terminal to the incoming service, using the correct size conductor and an appropriate bonding clamp. The connection must be made on the building side of the meter, as close as practical to the point of entry.
Typical cost: £150 to £350 per service, depending on the distance from the main earthing terminal and the routing required.
C2: Bonding Conductor Disconnected or Cut
A bonding conductor that was once connected but is now disconnected — typically because plumbing or gas work has disturbed it — receives the same C2 classification. The remedial work involves reconnecting the conductor to the correct point on the metallic pipe or, if the pipe has been replaced with plastic, rerouting the bonding to the nearest metallic section on the building side.
Typical cost: £100 to £250.
C3: Supplementary Bonding Missing in Bathroom
Where supplementary bonding is required in a bathroom but is not present, the inspector will note this as C3 (improvement recommended) unless the absence creates a specific danger, in which case it becomes C2.
Remedial work involves running supplementary bonding conductors — typically 4 mm² copper — between all exposed metalwork in the bathroom: pipes, radiators, baths, towel rails, metal window frames, and connecting them to the circuit protective conductor.
Typical cost: £200 to £500 per bathroom.
C3: Bonding Conductor Undersized
Older installations may have bonding conductors that are smaller than current regulations require. For example, a 6 mm² conductor where 10 mm² or 16 mm² is now required. The inspector will note this as a departure from current standards.
Remedial work: Replace the undersized conductor with one of the correct cross-sectional area.
Typical cost: £150 to £300 per conductor.
FI: Bonding Path Requires Further Investigation
Where the inspector cannot trace the bonding path — perhaps because it is concealed behind walls or runs through areas that are not accessible — a Further Investigation observation may be recorded. This means additional work is needed to establish whether adequate bonding exists, potentially involving lifting floorboards, removing access panels, or using specialist tracing equipment.
Typical cost for investigation: £100 to £200, plus any remedial work identified.
The Remedial Work Process
Fixing bonding defects is one of the most straightforward types of electrical remedial work. The materials are inexpensive, the installation is well-defined by regulations, and the work rarely causes significant disruption.
Step 1: Assessment
A qualified electrician reviews the EICR observations, visually inspects the existing bonding arrangements, and identifies exactly what work is needed. This often reveals additional issues the EICR did not specifically note — for example, a bonding conductor that is connected but uses an incorrect type of clamp.
Step 2: Installation
For main bonding, the electrician runs a conductor of the correct size — typically 10 mm² green-and-yellow insulated copper — from the main earthing terminal to each incoming metallic service. The conductor is routed neatly, clipped at regular intervals, and connected using BS EN 60947-7-1 compliant bonding clamps. Labels are fitted at each bonding connection and at the main earthing terminal.
For supplementary bonding, 4 mm² conductors are run between exposed metalwork, typically surface-clipped or concealed where practical. In bathrooms, connections are made to pipes, radiators, baths and any other exposed metalwork.
Step 3: Testing
After installation, the electrician tests the continuity of every bonding path using a low-resistance ohmmeter. The readings are recorded and should be well within the maximum permitted values.
Step 4: Certification
Bonding work carried out as remedial work following an EICR is typically documented on a Minor Electrical Installation Works Certificate. This provides formal evidence that the work has been completed to the required standard and should be kept with your EICR report.
Preventing Future Bonding Problems
Bonding defects often recur because non-electrical trades disturb the bonding without realising it. You can reduce this risk by informing plumbers, gas engineers and heating contractors that bonding conductors exist and must not be disturbed, asking them to notify you if they need to disconnect bonding to carry out their work, arranging for an electrician to reinstate bonding after any plumbing or gas work that involves altering pipework, and including bonding checks in your regular maintenance schedule.
For landlords and property managers, adding a bonding check to the schedule whenever a property undergoes plumbing work, boiler replacement, or bathroom renovation is a practical way to prevent bonding defects from accumulating between EICR inspections.
Costs Summary
| Bonding Work | Typical Cost | |-------------|-------------| | Main bonding — one service (gas or water) | £150–£350 | | Main bonding — reconnection after disturbance | £100–£250 | | Supplementary bonding — per bathroom | £200–£500 | | Undersized conductor replacement | £150–£300 | | Further investigation of concealed bonding | £100–£200 | | Full bonding remedial package (typical house) | £400–£800 |
Get Your Bonding Checked
If you have an upcoming EICR or your last report flagged bonding deficiencies, arranging remedial work now avoids the pressure of a deadline and ensures your property is safe.
- Call: 0161 302 1369 (Monday to Friday, 8 AM to 5 PM)
- Email: hello@manchestercompliance.co.uk
- Emergency line: 0161 302 1369
- Address: 25 Holden Clough Drive, Ashton-under-Lyne, OL7 9TH
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