Q2.1. What is Radioactive Lightning Protection?
Radioactive lightning protection is based on claims that a radioactive source around the head of an air terminal enhances its natural ion discharge which naturally takes place during a static build-up associated with lightning storms. This enhancement is claimed to be so great that it improves dramatically the ability of an air terminal to attract to itself a lightning strike.
This form of protection, however, has never been accepted by any international body and is disputed by many leading authorities on the subject.
The reports contained in the Furse document “papers on ‘Exotic’ lightning protection systems” confirms the view that a radioactive source has little, or no effect as a lightning protection unit.
The foreword in BS EN 62305 makes the following statement:-
‘it is recommended that the materials extent and dimensions of the air terminations, down conductors, earth terminations, bonding , components, etc. as laid down in this standard should be adhered to in full, irrespective of any devices or systems employed which claimed to provide enhanced protection”
In effect, researchers who have examined the various claims of ‘exotic’ systems have found them to have no scientific credibility.
Q2.2. Does copper attract lightning better than aluminium?
‘No’. The choice of materials for a lightning protection system is dictated by their resistance to corrosion, overall comparative costs and their compatibility with other metals used on the structure – not by material’s ability to attract lightning. Lightning will be attracted to any earthed conductive (metal) part of a structure in preference to a non-conducting material.
Q2.3. When using an aluminium system, does the conductor size have to be greater than when using copper?
According to BS EN 62305, ‘No, it doesn’t’. When a conductor is struck by lightning, the lightning current is of a high magnitude, flowing along the conductor for only a fraction of a second. The choice of material is not as important as in a continuous current carrying application. The minimum size recommended in BS EN 62305 is 50mm2 for both copper and aluminium. However our recommended practice is 70/ 75 sq. mm for cable and tape conductors respectively.
Q2.4. Can I mix circular/stranded conductor with tape conductor on my lightning protection system?
It is not normal practice to mix various types of conductors, but for instance, circular conductor can change to tape conductor at the test point.
Q2.5. Can I hide the system under the roofing?
BS EN 62305 permits the use of air termination conductors to be installed below the roof covering, but advocates that it is used in conjunction with 0.3m high bare vertical rods projecting through the roof.
Q2.6. When would I use a catenary wire suspended above the area to be protected?
It can be used in instances where a high degree of protection is required. For example, with high risk structures such as explosive factories, tank farms etc.
Q2.7. If you bond metal window frames, ducting, etc. into a lightning protection system, will these then become ‘live’ when lightning strikes, therefore, becoming potentially dangerous to any contents or persons nearby?
By not bonding any metal work close to the lightning protection systems, if lightning should strike , the voltage difference between the lightning conductor and the metalwork could cause a flashover, therefore, becoming ‘live’ and finding a dangerous and uncontrollable path to earth from this point.
By bonding all the metalwork into the lightning protection system, the voltage always remains the same, thereby preventing any flash-over and ensuring safety for contents and persons nearby.
Q2.8. Should the metal scaffolding on a building be protected against lightning?
Yes. BS EN 62305 strongly recommends that throughout the period of construction, all large and prominent masses of steelwork including scaffolding should be effectively connected to earth.
Q2.9 The IEC Code of Practice infers that horizontal roof conductors are sufficient. Why then should I use air rods?
BS EN 62305 does not regard vertical finals as essential except where dictated by practical considerations. The American Code, however, recommends the use of vertical finals. The choice of use is, therefore, governed, to a large extent, on which standard is being adopted.
At FullSpectrum Energy, we are uniquely positioned by experience and expertise to Advice, Design, Install, Commission Effective Lightning Protection and Quality Earthing System to international best practices irrespective of the sector and Standard.
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Victor Oyedu, FNSE, FNIEEE, CPQ.
Power Quality and Energy Management Specialist.
Publisher at Afrienergyonline.com
CEO, FullSpectrum Energy Solutions Limited, Nigeria.
