Earthing Bars – What They Are and What They Do

An earthing bar, also known as a ground bar, is an important component in many electrical systems. It provides a central point to connect multiple grounding conductors, helping manage electrical safety and interference. This guide will explore what earthing bars are, why they are used, their key features and how to choose the right one for your application.

An earthing bar is a metal strip, often made of copper, equipped with several terminals to connect grounding or earthing conductors. It creates a common bonding point to link multiple ground connections in an electrical installation into one consolidated bar.

What is an Earthing Bar?

Earthing bars are installed in many types of electrical systems, equipment and enclosures. Some common examples include:

• Switchboards and distribution boards
• Motor control centres (MCCs)
• Control panels and field enclosures
• Equipment racks and metal frames
• Telecom cabinets and shelters

The main purpose of an earthing bar is to provide a solid, low impedance ground reference in an electrical system. This ground reference helps maintain safety and protects equipment by diverting wayward electrical currents away from devices and people.

Why are Earthing Bars Used?

There are several important reasons earthing bars are commonly installed in electrical systems:

Electrical Safety

Having a solid, consolidated earthing point is vital for safety. It provides a path to earth for fault currents, reducing the risk of electric shock. Earthing bars connect all metal components to ground, preventing dangerous voltage on racks, panels and device enclosures if an electrical fault occurs.

Controlling EMI/RFI

Grounding through an earthing bar helps minimise electrical noise interference, known as EMI (electromagnetic interference) and RFI (radio frequency interference). Any electromagnetic noise or stray currents induced in the system will be shunted away to ground. This is important for maintaining signal integrity and avoiding interference issues.

Lightning Protection

In outdoor installations, earthing bars help dissipate lightning strikes and other high voltage surges safely to earth. Connecting all metalwork and electrical devices back to a common earthing point is essential to handle these potentially damaging voltage spikes.

Avoiding Ground Loops

Using an earthing bar creates a single point of contact with the earth ground plane. This avoids ground loops, which occur when electrical devices make multiple, separate connections back to ground. Ground loops can induce noise currents and interfere with signals.

Key Features of Earthing Bars

Earthing bars have some common design features and properties that suit them to their purpose:

• Made of conductive metal, usually copper or aluminium. This ensures high electrical conductivity.
• Multiple binding posts or terminals. 6-24 terminals are common, allowing many ground conductors to be consolidated at one point.
• Large conductive surface area. The actual metal bar is sized to handle expected fault currents without overheating.
• Mechanical strength for durability. Earthing bars are securely mounted and made of rigid metal to withstand physical damage or movement.
• Corrosion resistance. Materials and platings (e.g. tin) are chosen to prevent long term oxidation and degradation. Stainless steel bars are popular.

-Certified to relevant safety standards. Bars are tested to required standards such as UL, CSA, IEC and verify they can handle expected fault currents.

• Sized to suit the electrical system. Different current ratings are available to safely earth small control panels or huge switchboards.
• Electrically bonded to the enclosure. The bar is securely connected to the earthing point of the metal cabinet or frame it is mounted in.
• Permanent, reliable connections. Screws, bolts or lugs are used to make high integrity, corrosion-resistant joins to ground conductors.

Choosing the Right Earthing Bar

Here are some key factors to consider when selecting an earthing bar:

Electrical System and Fault Current Rating

The prospective short circuit current that could occur if a major electrical fault happens needs to be estimated. The earthing bar must have sufficient ampacity to carry this current for the duration required to clear the fault through overcurrent protection devices. Higher rated bars are used for systems with higher available fault currents.

Number of Connections Needed

The earthing bar must provide enough terminals to consolidate the ground conductors required in the electrical system. As a rule of thumb, choose a bar with 20% more terminals than immediately needed to allow for future expansion.

Enclosure Type and Mounting

Earthing bars need to be securely mounted, so the mounting style must suit the enclosure. Common mounting options include screw-fixed, DIN-rail mounting, and mounting feet for bolt-through panel mounting.

Environmental Factors

For outdoor or wet area installations, earthing bars with greater corrosion resistance are preferable, such as stainless steel. Harsh chemical or abrasive environments also require bars with coatings that protect against degradation.

Mechanical Strength

In physically demanding applications with vibration, shocks or extreme temperatures, copper alloy or steel earthing bars provide maximum mechanical durability and strength.

Cost

Copper earthing bars provide the best electrical conductivity. However, aluminium or tin-plated steel bars can be used to reduce cost in lower rated applications not requiring ultimate conductivity.

Relevant Approvals and Standards

Check that the earthing bar is certified to all required electrical equipment standards for your country and application. This ensures safety and compliance with the electrical code.

Installation of Earthing Bars

When installing an earthing bar, there are some key guidelines to follow:

• Select suitable mounting location. This is typically near the bottom rear of the enclosure and close to the main earthing point.
• Mount the bar securely using manufacturer recommended fasteners. This usually involves bolt-through to structurally sound points.
• Make sure it is electrically bonded to the enclosure earth using star washers and appropriately sized bonding conductors.
• Use appropriately sized cables for all earth connections to equipment. Overly long or undersized cables increase resistance.
• Use proper earth cable terminals, lugs, clamps or bolts to make high integrity connections.
• Make connections following a logical sequence from top to bottom or left to right. Neat connections aid testing and maintenance.
• Label all earth cables clearly at both ends following electrical code and standards.
• Carry out earth continuity testing to verify resistance is within acceptable limits after installation.

Properly installing earthing bars helps create a safe, reliable grounding system and prevents many common electrical hazards.

Earthing Bar Testing and Maintenance

While earthing bars are designed for reliable, long-term performance, periodic testing and maintenance helps confirm their integrity:

• Continuity Testing: Use a multimeter or earth tester annually to measure resistance from the earthing bar to the system earth. Resistance should be below 0.1 ohms in most electrical systems.
• Connection Inspections: Check earth connections at the bar routinely for any loosening, corrosion or damage. Re-tighten or replace affected lugs or cables.
• Cleaning: Wipe down earthing bars occasionally to prevent accumulation of dust, grease and other contaminants which can degrade connections.
• Bolt Torque Checks: Periodically check tightness of mounting bolts and connections to specified torque settings.
• Reload Protection: For bars using disconnecting links, check proper operation and replace fuses or links if faults occur. This protects the bar from damage.
• Enclosure Bonding: Confirm the earthing bar has a suitably-sized bond connecting it securely to its enclosure earth point.

Following the manufacturer’s maintenance recommendations helps maximise longevity and performance.

Examples of Earthing Bar Applications

Earthing bars are applied in diverse electrical installations. Some typical applications include:

Switchboards

Large main switchboards have a vital need for consolidated earthing. An earthing bar safely connects all the system ground conductors, enclosure metalwork and cable armouring that terminates in the switchboard. High capacity copper earthing bars are normally used.

Motor Control Centres

Industrial motor control centres contain multiple motor controllers in a single assembly. An earthing bar bonds all the motors and metallic sections together, preventing a shock hazard. It also helps reduce electromagnetic interference.

Equipment Racks and Frames

Connecting rack-mounted electronics or telecommunications equipment to a shared earthing bar helps avoid interference issues. It also protects sensitive devices from unplanned voltage spikes.

Battery Banks

In battery rooms and UPS systems, earthing bars safely connect the multitude of battery units to ground. This is crucial to handle potentially enormous fault currents from shorted battery strings. Copper earthing bars are preferred for maximum fault current capacity.

Telecom Shelters

Outside plant telecom shelters and huts rely on an earthing bar to ground cable shields and protect sensitive electronics from lightning surges coming down the cabling. A good grounding strategy is essential for reliability.

Machinery and Vessels

On large machines, vehicles and seafaring vessels, earthing bars provide a common grounding point for control systems, power systems and electronics. This enables proper function and safety. Stainless steel earthing bars withstand harsh conditions in these applications.

Summary

Installing suitable earthing bars is a fundamental part of creating safe, reliable electrical systems. Earthing bars consolidate ground conductors to manage fault currents, reduce EMI/RFI noise, avoid ground loops and protect equipment.

Choosing the right bar depends on factors like the fault current rating, number of connections required, mounting style and environmental conditions. Following best practices for installing and maintaining earthing bars helps achieve a low resistance earthing system.

Earthing bars are found across many industries wherever robust electrical grounding is needed. Whether it’s an industrial facility, telecoms site, commercial building or marine vessel, earthing bars play an important role in managing electrical safety and performance.