What is Lightning Protection?

What is lightning protection and how does it work? 

Lightning protection is a system that’s put in place to protect a structure or a building from lightning damage, and to protect either persons or livestock inside or around the building. 

Lightning strikes can result in large impulse currents up to 200kA. Left to their own devices, these currents create electrical arcs and cause huge amounts of heat. They are highly unpredictable and can cause damage to buildings and even loss of life. 

A lightning protection system works by attracting the lightning strike to a dedicated conductor, such as copper or steel, that disperses the currents to the ground in a controlled and safe manner. 

There are three elements to a lightning protection system. They are:

  1. Air termination - hits this first, collects the strikes
  2. Down conductor - takes current from air termination, to the earth termination
  3. Earth termination - current disperses to ground


How do you protect buildings from lightning strikes?

You protect buildings from lightning strikes using a lightning protection system, which controls the lightning current.

What is the importance of grounding in lightning protection?

Lightning must reach the ground - this is where it is trying to get to. Lightning uses ground as its whole conductor. A lightning protection system means that it gets to the ground and the current is dispersed safely. No part of the system will work without the other. 

The grounding system is integral to a modern electrical lightning protection system. Without it, lightning can cause danger and damage including ground faults, loud electrical noises, damage to buildings, fire and personal injury.

In some instances the earth termination system will need to consider touch and step voltages to provide a safe environment. 

What are the principles of earthing in lightning protection?

Earthing is fundamental to a lightning protection system. It is the part of the system that terminates the current and transfers it safely to the ground. 

In most instances in the UK you can use an earth rod or series of earth rods to earth a lightning strike. The earth termination system is required to have an overall resistance of less than 10 ohms.

In some instances a more complex earthing system is required. For example, where there are hazardous areas in a building you have to use a perimeter earth electrode that surrounds the structure, this consists of horizontal buried electrodes. 

Where a site has a high voltage earth system you may be able to use this for the lightning protection earth termination system.

How does a lightning arrester work?

A lightning arrester is unique to a high voltage system. A lightning arrester diverts an impulse to earth rather than allowing it to continue down the phase conductor. 

How does surge protection work?

A surge protection device (SPD) works with a low voltage system. It temporarily shorts the phase conductor to earth, however in this system the impulse current is on the earth conductor rather than the phase conductor, as in a lightning arrester.  

Both a lightning arrester and a surge protection device stop a surge or impulse current propagating any further down the circuit.