Earth Bar Fundamentals

Earth bar role in earthing measurements and LPS inspection
Electrical power systems are responsible for delivering electricity from generators to the end-consumer. Protection of these systems is necessary to ensure safety of personnel, to protect expensive assets and to ensure continuity of supply. Earth bars play a key role in the specialist systems designed to protect networks from fault conditions. In this article, we will look at 1) Where earth bars fit into the wider protection system 2) What an earth bar is and its basic construction, 3) Factors to consider when selecting earth bars.
Earth Bars: Role in The Protection System

Faults can occur anywhere on the system but are most common on outdoor transmission lines. Such faults are usually characterised by extremely high currents. Although the power system can protect itself from such faults (e.g., using overcurrent or distance protection), there may be short periods where extremely high currents are present. These high currents can lead to dangerously high step and touch voltages which can lead to injury of nearby personnel. Providing a low impedance path to ground is a key mitigation measure to minimise such risks.

The term “earthing system” normally used to describe the collection of assets responsible for dissipating fault current to earth. The earth bar plays a key role in this system as a common connection point to which all conductive components are connected. Among many other functions, an earth bar (also known as cut-off bar) disconnect the earthing installations for inspection and measurement purposes, as represented in Figure1.
Earth bar role in earthing measurements and LPS inspection
Figure 1. Earth Bar Role in Earthing Measurements and LPS Inspection

This figure illustrates a representation of an earth bar and shows its state during the measurement of the earthing resistance. It should be noted that several earth bars may exist in the same installation.

What is an Earth Bar?

Quite simply, an earth bar is a strip of metallic conductor designed to be a common point to which all conductive components and services, such as water and gas pipes, power, telecommunications, and data cables should be connected.

Standard earth bars are an efficient and convenient way of providing a common earth point. These bars are usually designed in accordance with a specific application. For instance, telecoms earth bars (right in Figure 2) differ than industrial/power earth bars.

Figure 2. Example of Earth Bars With Single Disconnecting Link, Earth Bars With Double Disconnecting Link, and A Telecom Earth Bar

The twin disconnecting links are mainly used to offer a temporary break in the connection to the earth, allowing the inspection and testing of multiple earth rods/systems while disconnecting them from the lightning protection and earthing system.

Earth Bar Selection

Earth bars must be adequately selected by considering various aspects. The first thing to mention is that an earth bar consists of materials used in earthing systems. Therefore, it must be able to provide a low impedance path to earth carry the maximum fault currents. In addition, it should resist corrosion and withstand mechanical damage.

A base made of GRP (Glass Reinforced Polyester) is usually used in earth bars to provide mounting and insulation from metallic surfaces. It also makes the earth bars easier to handle.

The careful selection of the material, cross-sectional area, and dimension some of the many factors that should be considered by experienced personnel in accordance with national and international standards. Thus, Kingsmill Industries have offered several designs to meet the requirements of the protective systems in any given installation.

Earth Bars: Factors to Consider

All conductive components and services, such as water and gas pipes, power, telecommunications, and data cables should be connected to a single earth bonding bar (i.e., equipotential bonding). For this reason, every earth bar should be installed in a way to allow easy access for testing and inspection, as represented in Figure 3.

Earth bars should be installed in the basement or approximately at ground level where insulation requirements are not fulfilled. Each earth bar should be connected to the earthing system via the most direct route as represented in Figure 4.

Example of the earth bars position within a structure
Figure 3. Example of The Earth Bars Position Within A Structure

Regarding the location of the earth terminal bar (or, the main earth bar), a provision should be considered for future earth bar connection, remembering that it is also facilitating the interconnection between the actual system and any future installation.

It is good practice to make sure that every earth bar is above ground, installed as a bolted connection and is in a safe area to avoid corrosion. According to the BS EN 62305-3, however, an earth bar of an isolated external LPS should be installed at ground level only.

It should be noted that more than one earthing bar can be installed in the same structure. This is normally for large structures of more than 20 m in length as stated by the standard [BS 62305-3]. In this case, all earth bars should be interconnected, and a ring earth bar may be used.

Example of the earth bars connection to the earth-termination system
Figure 4. Example of The Earth Bars Connection to The Earth-termination System

[1] British Standard Publications, Code of practice for protective earthing of electrical installations, BS 7430.
[2] British Standard Publications, Requirements for Electrical Installations. IET Wiring Regulations, BS 7671.
[3] British Standard Publications, Protection against lightning Part 3: Physical damage to structures and life hazard, BS EN 62305.

kingsmill logo

Down to Earth keeps you updated and explains all things related to Earthing and Lightning Protection. We care about keeping you and your structures safe, and to do so, we ask our top specialists to share some of their know-how regarding products and installations. We are always ready to get Down to Earth! We’ve got you covered! Make sure to subscribe to our newsletter to keep up with our latest articles and information about lightning protection.

Subscribe to our Blog