Bonding vs Earthing in Electrical Installations

Bonding vs Earthing in Electrical Installations

A Technical Guide for Electricians According to SANS 10142-1

One of the most misunderstood topics in electrical installations is the difference between earthing and bonding.

Although these two concepts work together as part of the electrical protection system, they serve very different technical purposes. Misunderstanding their functions can lead to:

• Failed Certificates of Compliance (COC)

• Dangerous touch voltages

• Protective devices not operating correctly

• Non-compliance with SANS 10142-1

For the electrician signing a COC, understanding the regulatory intent behind earthing and bonding is essential.

1. The Regulatory Framework

Earthing and bonding requirements in South Africa are mainly governed by:

• SANS 10142-1:2024 – The Wiring of Premises

• SANS 60364-7-712 – Solar PV installations

Within SANS 10142-1, the key areas covering earthing and bonding include:

• Earthing terminals and connections

• Earthing arrangements and earth continuity conductors

• Inspection and testing requirements

The standard requires that earthing arrangements must provide a connection to earth that:

• is reliable

• can carry earth fault currents

• prevents electric shock hazards and thermal stresses

Protective earthing and equipotential bonding therefore form one integrated safety system within the installation.

2. Protective Earthing

Definition

Earthing is the intentional electrical connection between the electrical installation and the general mass of earth.

Its purpose is to provide a low impedance path for fault currents so that protective devices such as circuit breakers and earth leakage devices can operate quickly.

The earthing system must be capable of carrying prospective fault current without excessive temperature rise during the disconnection time. 

Main Components of an Earthing System

Main Earthing Terminal (MET)

The main earthing terminal is the central point where all earthing and bonding conductors connect.

It typically includes connections from:

• earth electrode

• earth continuity conductors

• equipotential bonding conductors

• lightning protection systems

• telecommunications earthing conductors

The MET forms the reference point of the entire earthing system.

Earth Continuity Conductors (ECC)

Earth continuity conductors connect exposed conductive parts of electrical equipment to the earthing system.

Their function is to ensure that when a fault occurs between a live conductor and a metal part, the fault current flows safely through the earth conductor.

These conductors must:

• have sufficient cross-sectional area

• maintain continuity under fault conditions

• comply with cable standards and installation rules

Earth Electrodes

An earth electrode provides the physical connection between the installation and the earth.

Examples include:

• earth spikes

• earth plates

• foundation earthing

Foundation earthing is considered one of the most effective earthing methods where available. 

3. Equipotential Bonding

Bonding refers to the connection of conductive parts together so that they remain at the same electrical potential.

This is known as equipotential bonding.

The objective is to prevent dangerous touch voltage between metal parts that could otherwise be at different voltages.

Bonding therefore protects people by ensuring that two conductive parts touched simultaneously cannot have a hazardous voltage difference.

Examples of conductive parts requiring bonding include:

• metal water pipes

• gas pipes

• structural steel

• cable armouring

• PV mounting structures

• metal service pipes entering the building

4. Minimum Bonding Requirements (According to SANS 10142-1)

Equipotential bonding is one of the most critical safety measures in electrical installations.

SANS requires that extraneous conductive parts entering or forming part of the building structure must be bonded to the main earthing terminal so that they form part of the installation’s equipotential bonding system.

Where an accessible bonding terminal is provided for other services such as telecommunications systems, it must be connected to the main earthing terminal using a copper conductor of at least 6 mm². 

This prevents external conductive systems from introducing dangerous voltage differences into the installation.

Bonding of Metal Water Pipes

Metal water pipes entering a building are classified as extraneous conductive parts.

They must be bonded to the earthing system to prevent voltage differences between the plumbing system and the electrical installation.

The bonding connection should:

• be installed near the point where the pipe enters the building

• be mechanically secure

• use approved bonding clamps

• be connected to the main earthing terminal

This requirement typically applies to:

• copper pipes

• galvanized steel pipes

• stainless steel pipes

Where the piping system is entirely plastic, bonding may not be required. However electricians must always confirm that metal fittings or valves are not present, as these can reintroduce conductive paths.

Bonding of Gas Pipes

Gas pipes must also be bonded because they can introduce stray voltage into the building.

If potential differences occur between gas pipes and other conductive parts, sparks could ignite flammable gas.

Gas pipe bonding therefore reduces both electric shock risk and explosion risk.

Bonding of Structural Steel

Structural steel used in buildings can also form part of the equipotential bonding system.

Reinforcing steel embedded in concrete may be integrated into the earthing and bonding system when correctly connected to the earthing terminal. 

This practice is common in:

• commercial buildings

• warehouses

• reinforced concrete structures

It can significantly improve the performance of earthing systems and lightning protection systems.

Bonding of Cable Armour and Metallic Sheaths

Electrical cables with metallic components must also be bonded.

Examples include:

• steel wire armoured cables

• metal cable sheaths

• cable trays

• metal trunking systems

Bonding ensures that if a live conductor faults to the armour or metal enclosure, the protective device will operate quickly.

Bonding in Bathrooms and Wet Locations

Bathrooms and wet areas present a higher risk of electric shock due to the presence of moisture and increased body conductivity.

Additional equipotential bonding may therefore be required between:

• metal baths

• metal water pipes

• heating pipes

• structural steel

This ensures that anyone touching multiple conductive parts will not be exposed to dangerous voltage differences.

Bonding of Solar PV Structures

Solar PV systems introduce large metallic structures exposed to environmental conditions.

All metallic PV module frames and mounting structures must be bonded together and connected to the main earthing terminal of the installation.

Where a separate PV earth electrode is installed, it must still be connected to the main earthing system to maintain equipotential bonding. 

The bonding conductor used for PV mounting structures must have a minimum cross-section of 4 mm² copper. 

5. Testing Requirements for Bonding and Earthing

Earthing and bonding systems must be tested during inspection and certification.

Bonding conductors must be tested using a test supply between:

• 4 V and 24 V

• minimum 0.2 A

The measured resistance must not exceed 0.2 Ω. 

Earth continuity conductors must also be tested to confirm that the resistance between the distribution board earth terminal and the point of consumption meets the limits specified in SANS 10142-1. 

6. Critical Limitation: Neutral and Earth

One of the most important rules electricians must follow is:

Neutral and earth may not be connected together on the load side of the point of control. 

Incorrect neutral-earth connections can cause:

• circulating currents

• nuisance tripping

• dangerous voltages on metal parts

This is one of the most common faults discovered during inspections.

7. Practical Example – Geyser Installation

A typical compliant geyser installation includes:

• an earth conductor connected to the geyser casing

• bonding between the hot and cold water pipes

• connection of these pipes to the earthing system

This ensures that all metal parts remain at the same electrical potential, even during fault conditions.

8. The Electrician’s Legal Responsibility

When a registered person signs a Certificate of Compliance, they confirm that:

✔ earthing is correctly installed
✔ equipotential bonding is present
✔ earth continuity is verified
✔ test results comply with SANS requirements

Failure to verify these systems can lead to:

• injury or fatality

• legal liability

• invalid COC

Earthing and bonding are therefore not just technical requirements — they are legal safety obligations.

Final Thought

A safe electrical installation is not defined only by the wiring or circuit breakers.

The true backbone of electrical safety is the earthing and bonding system.

Earthing ensures that fault currents have a path to earth, allowing protective devices to operate.

Bonding ensures that all accessible conductive parts remain at the same electrical potential, preventing dangerous touch voltages.

When installed and tested correctly, these systems create the equipotential environment that protects both the user and the electrician.