Lightning Risk Assessment (IEC 62305) 

By on

IEC 62305 'Protection against lightning' requires a risk assessment be carried out to determine the characteristics of any lightning protection system to be installed. There is a lot of hype about about this being a complicated process, however in reality it is very simple.

Risk Assessment

The procedure requires assigning a tolerable level of risk. A lightning protection level is then chosen to ensure that the calculated risk level is lower than the assigned tolerable level.  This is carried out for each of the following risk types:

  • Loss of Human Life
  • Loss of Public Services
  • Loss of Cultural Heritage
  • Economic Loss

Each country defines it's own tolerable risk values (for example the UK assigns the tolerable risk for loss of cultural heritage as 10-4).  General representative values listed in the standard are:

Type of Loss

Tolerable Risk

Loss of human life or permanent injuries

10-5

Loss of service to the public

10-3

Loss of cultural heritage

10-3

Economic loss

10-3

 

Note: surge protective devices (SPD) when installed, can lower the calculated risks obtained during any assessment exercise.

Lightning Protection Level (LPL)

Four protection levels (I, II, III and IV) are defined by considering the peak current, charge, specific energy, duration of various lightning strokes and the probability of these being exceeded.  Lighting Protection Level I is the most severe, with level IV being the least.

Once a lightning protection level has been selected, this fixes many of the parameters for the design and installation of the system.  For example, the size of the rolling sphere for calculating protection zones is 20 m for a protection level of I, and increases to 60 m for level IV.

Calculation

After reading the standard, calculating the risk level may seem like a complicated process. Help is at hand however. In purchasing the standard the 'IEC Risk Assessment Calculator' software is provided free of charge. This is a very straightforward piece of software to use requiring the structure dimensions to be entered and various parameters selected from drop down lists. The entire process can be completed in only a few minutes and assessment reports generated.

The attached images show the input screen for the software and an example of the assessment report generated. Click on the images to view a bigger picture. this being a complicated process, however in reality it is very simple.

Related Links

The standard can be purchased at:

IEC Risk Assessment Calculator

 

Lightning Assessment Report 1.2

 

Lightning Assessment Report 2.2

 



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



Copyright Infringement

myElectrical does not support or promote the use of copyrighted material without the copyright owner's consent. If you believe that material for which...

Low Voltage Circuit Breakers

Circuit breakers are switching devices whose primary function is to isolate parts of an electrical distribution system in the even of abnormal conditions...

Getting Started with Patents

If you have a great idea or invent something the last thing you want is someone to steal the idea. One of the things you can do is protect the intellectual...

Gas Insulated or Air Insulated Switchgear

Various arguments exist around SF6 Gas Insulated (GIS) and Air Insulated (AIS) medium voltage switchgear. Recently we had to change a GIS design to AI...

Cable Sizing Tool

Our cable sizing tool is one of the more popular tools on the site.  The tool enables cables to be sized in compliance with BS 7671 (the IEE Wiring Regulations...

Photovoltaic (PV) - Electrical Calculations

Photovoltaic (PV) cells (sometimes called solar cells) convert solar energy into electrical energy.  Every year more and more PV systems are installed...

The ac resistance of conductors

In a previous article I looked at the dc resistance of conductors and in this article we turn our attention to ac resistance. If you have not read the...

Meeting room of the future

The IET site has a video of a visit showing of a high tech meeting room developed at Napier University in Edinburgh. It a good demonstration of innovative...

Thomas Edison

American inventor Thomas Alva Edison was born in Milan, Ohio on February 11, 1847. He was the youngest of seven children and received little formal schooling...

Why is electricity so hard to understand?

It's been a busy few months on different projects or busy couple of decades depending on how I look at it. I can say that on the odd (frequent) occasion...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note