Posted By David Morton
Can I give you a lead in and some background to the development of 62305 for the UK and some good news at the end.

BSEN 62305 is a document as you know which has been introduced to replace BS6651. It was necessary that UK PLC had an input into this proposed standard and as such our Lightning Conductor Industry governing body ATLAS (Association of Technical Lightning and Access Specialists) reviewed this document in conjunction with the BSI via our in house Lightning Conductor Committee.

This committee lead by our chairman Mr John Sherlock of Furse Thomas & Betts has been reviewing and developing 62305 for over two years with specific emphasis on the Risk document 62305-2. and our monthly meetings necessitated long hand sample risk calculations to ensure that our UK parameters were correct.

BSEN 62305 retains its original CENELEC format but of course now contains UK parameters.

The worked examples (Case Study for Structures) provides an excellent guide to long hand calculation but better still is the software being developed by Furse Thomas & Betts which will take all the hard work out of the calculation. Please do not think that this software is a total solution however, far from it, you still need answers for around 16 risk elements to input into the software, if you do not get all these answers or the answers are incorrect your design level of protection will be wrong and so will your Surge Protection Level (Mandatory Element) and of course the eventual cost (you wont get the money back later).

Sorry if the above is a bit basic but as you are probably aware the documents are too in depth for practical explanation here however I can direct you to our Federation Technical Committee via email at info@atlas-1.org.uk Tel 0115-955-8818.

If you need more information on the Furse Software contact them on enquiry@furse.com Tel 0115-964-3800

Regards
David J Morton
Regional Director
www.bestservices.org.uk

Posted By David Morton
One of the 16 or so parameters or weighting factors required for the determination of the level of lightning protection ie Level 1, 2, 3 or 4 is Hz Table NC.5 in 62305-2.

You will note from this table that as the panic level or hazard level increases so does the numeric value (multiplying factor).

On a practical basis it is considered that a weighting factor of say 5 would give an average panic level and with all the other factors taken into consideration this would generally be considered to be say a level 2 design.

If you consider therefore that any lightning strike to your project should be rated at a multiplying factor of say 20 or even 50 these multiplying factors would take you well into the level 1 protection category for both lightning protection and coordinated surge protection devices.

Choosing the highest level of lightning protection etc would not be inappropriate for a special hazard of 20 or 50 (as appropriate).

By the way, you will also note the multiplying factor of Rf is the highest factor from table NC.4 and you can see from the multiplying factor of 1 for your project!!! that this weighting factor will again push you towards the level 1 lightning protection when compared with the .005 value which of course has a much smaller influence on the result (lower level lightning protection).

As stated previously there are at least 16no weighting factors/multiplying factors to input into the calculation but it is fair to say that potentially hazardous petrochemical sites will generate the higher numerical factors putting level 1 lightning protection as the preferred level.

The risk assessment whilst giving you the preferred level of lightning protection will not of course help when applying the design intent (62305-3) in terms of separation distances for dangerous sparking and surge protection devices (62305-3 and -4) these must be evaluated, for want of a better word, separately.

Hope the above gets you a bit further on

Regards
David Morton