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



Autonomous Vehicle Challenge

Two driverless and solar power vans have departed from Italy on their way to China via the silk road. During the 13,000 kM trip the vans will drive themselves...

Cost Performance and Time

Often us engineers get so bogged down in equations, using software, producing drawings and writing specifications that this becomes the sole focus.   ...

MIT OpenCourseWare

MIT OpenCourseWare, makes the materials used in teaching all MIT subjects available on the Web, free of charge, to any user in the world.

Cable Sheath and Armour Loss

When sizing cables, the heat generated  by losses within any sheath or armour need to be evaluated. When significant, it becomes a factor to be considered...

Electric Motors

Collection of links to various places with useful motor information. I’ll try and return to the page every now and again to update it with any motor notes...

Lightning Protection and Earth Electrode Resistance

Most installations involve some form of lightning protection system which is connected to an earth electrode.  The function of the earth electrode is to...

Calculating Cable Fault Ratings

When selecting a cable, the performance of the cable under fault conditions is an important consideration. It is important that calculations be carried...

Multimeter

Multimeters are undoubtedly the most common item of electrical test equipment in use.  Often it is the first piece of equipment people will turn to when...

How Electrical Circuits Work

If you have no idea how electrical circuits work, or what people mean then they talk about volts and amps, hopefully I can shed a bit light.  I’m intending...

IEEE Winds of Change

IEEE TV has a part series of videos on wind power and it's implication. For a really good overview to the technologies and issues around wind power, these...

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