Earthing & Lightning Protection ABB (UK)

Earthing & Lightning Protection UK solutions overview

Dia – 25 mm
Size – 762 mm
Base – 102 mm

Purpose of Conventional LPS (Franklin Rod)

The primary function of a conventional LPS is to protect a structure from lightning damage by providing a low-resistance path to the ground. The system intercepts lightning strikes before they can hit a building or other sensitive structures and safely diverts the electrical current into the earth.

Working Principle

The Franklin Rod System operates based on the concept of direct interception of lightning strikes. It consists of multiple rods or air terminals placed at strategic high points on the structure, where they serve as preferred attachment points for lightning.

How it Works

Charge Attraction: During a thunderstorm, a large potential difference develops between the charged storm cloud and the ground. This creates an electric field that intensifies around the highest points of a structure.
Interception: The Franklin rod, being a conductive material, attracts the lightning strike to itself rather than allowing it to hit vulnerable parts of the structure.
Energy Dissipation: Once the lightning strike is intercepted by the rod, the electrical energy is conducted down through a series of conductive cables (down conductors) to the grounding system, where the energy is safely dissipated into the earth.

Components of a Conventional LPS

A typical Franklin rod-based lightning protection system consists of the following components:

Air Terminals (Franklin Rods): These are pointed metal rods made of conductive material such as copper or aluminum. The rods are installed at the highest points of a structure, such as the rooftop or towers. Their primary function is to intercept lightning strikes.
Down Conductors: These are conductive cables (usually copper or aluminum) that provide a low-resistance path from the air terminals to the ground. They run along the sides of the building, connecting the air terminals to the earthing system.
Grounding (Earthing) System: The grounding system ensures that the electrical energy from a lightning strike is safely discharged into the earth. It typically consists of ground rods or plates buried deep into the soil. The resistance of the grounding system is kept low to ensure efficient dissipation.
Bonding: To prevent side flashes (sparks between conductive parts due to voltage differences), all metallic parts of the building and system are electrically bonded together to maintain equipotential grounding.

Advantages of Conventional LPS (Franklin Rod)

Simple and Effective: The Franklin rod system is a time-tested, simple, and reliable method of lightning protection.
Cost-Effective: The conventional LPS is generally less expensive to install and maintain compared to more advanced systems, like Early Streamer Emission (ESE) systems.
Low Maintenance: Once installed, conventional lightning protection systems require minimal maintenance apart from periodic inspections and testing of the earthing system.
Wide Application: Conventional LPS can be used on almost any type of structure, from small residential buildings to large industrial complexes.

Installation Guidelines

Proper installation is key to the effectiveness of a Franklin rod-based lightning protection system. Here are the general guidelines:

Placement of Air Terminals: Franklin rods should be placed at the highest points of the structure, such as chimneys, rooftops, or towers. They should be spaced at regular intervals to ensure adequate coverage.
Height Considerations: The rods must extend above the structure to provide effective protection. The height of the rods determines the radius of protection, with the “zone of protection” generally following a 45-degree cone around the rod.
Number of Rods: For large buildings or structures with irregular shapes, multiple rods may be required to ensure complete coverage.
Path for Down Conductors: The down conductors must be arranged in a straight and direct path from the rods to the earthing system to minimize the resistance.
Earthing Requirements: The earthing system must have low resistance, typically less than 10 ohms, to ensure effective dissipation of the lightning energy. Ground rods or grounding plates are buried deep into the earth to provide the necessary resistance.

Standards and Compliance

Conventional LPS systems must be designed and installed in compliance with national and international standards to ensure safety and effectiveness. Some of the key standards include:

NFPA 780: National Fire Protection Association’s standard on lightning protection systems.
IEC 62305: International Electrotechnical Commission’s standard for lightning protection.
UL 96A: Standard for installation of lightning protection systems by Underwriters Laboratories.

These standards provide guidelines on the installation of air terminals, down conductors, grounding, and bonding to ensure the system is effective in protecting the structure from lightning strikes.

Applications of Franklin Rod LPS

Conventional lightning protection systems are widely used in various sectors due to their simplicity and cost-effectiveness. Common applications include:

Residential Buildings: Particularly homes in areas prone to thunderstorms and lightning.
Commercial Buildings: Office buildings, shopping malls, hotels, and other high-rise structures.
Industrial Facilities: Factories, warehouses, and plants that contain flammable materials or sensitive equipment.
Public Infrastructure: Schools, hospitals, airports, and government buildings.
Historical and Monumental Structures: To protect landmarks, churches, and historical sites.

Key Considerations for Conventional LPS

Structural Height and Shape: Taller buildings and those with irregular shapes may require multiple rods and carefully planned conductor paths to ensure complete protection.
Grounding Resistance: Proper earthing is critical. The effectiveness of a conventional LPS depends largely on the quality of the grounding system.
Maintenance and Inspection: Routine inspections, particularly of the grounding system, should be conducted to ensure that the system remains effective over time.

Maintenance

Regular maintenance ensures the longevity and effectiveness of the system. Maintenance tasks include:

Visual Inspections: Regularly inspect the air terminals, conductors, and grounding connections for signs of corrosion, damage, or wear.
Testing Ground Resistance: Annual testing of the earthing system’s resistance is essential to ensure it remains within acceptable limits (typically below 10 ohms).
Repair and Replacement: Any damaged components, such as corroded rods or broken down conductors, should be repaired or replaced immediately to maintain system effectiveness.

Limitations of Conventional LPS

Limited Protection Radius: Unlike Early Streamer Emission (ESE) systems, the protection zone offered by conventional LPS is limited to the immediate area around the air terminals.
Side Flashes: If bonding is not properly done, lightning can jump between nearby conductive materials (such as pipes and wires), posing a risk to people and equipment.
Aesthetic Impact: The installation of multiple rods, conductors, and ground connections on a building may affect its aesthetics, especially on historical or architecturally significant structures.