Q3.1. Non-metallic DC clips. Do they comply with the British / IEC Codes of Practice?
The Code merely states that, where non-metallic fixing materials are used, and then consideration should be given to their possible degradation due to ultraviolet light, frost, etc. Quality clips are manufactured from a high- grade polypropylene which exhibits excellent mechanical and thermal properties. They provide a high resistance to ageing when exposed to ultraviolet light over many years.
Q3.2. If a roof conductor is painted; does this impair its efficiency?
In our opinion, any covering that acts as an insulator will impair its efficiency. The extent of the reduction of efficiency is dependent upon the characteristics and thickness of the material. However, BS EN 62305 advocates the use of bare conductors for air termination networks wherever possible. If for, say corrosion reasons, a covering is required, a PVC coating or painting is permitted.
Q3.3. Can down conductors be run behind marble cladding?
This depends upon whether there is sufficient air gap between the outside frame of the structure and the decorative cladding, and how it is fixed. If there is insufficient movement of free air behind the cladding, it may be inadvisable to install the down conductors there, due to the mechanical forces created by the shock wave during a discharge, causing cladding to be dislodged. Further information regarding these mechanical effects can be found in BS EN 62305
Q3.4. Can I run the down conductor through a lift shaft, or use the lift guide rails as a down conductor?
‘No’. BS EN 62305 strongly advises that lift shafts should not be used for this purpose. Down conductors may be housed in an air space provided by a non-metallic, non-combustible internal duct and taken straight down to ground.
Q3.5. When an aluminium system is used, what is the best way to connect to the copper earthing?
The mating surface of the aluminium should be cleaned thoroughly by wire brushing and approved grease or jointing compound applied. The copper surface should be hot tinned and two mating surfaces bolted together. The complete joint should then be protected from the ingress of moisture by the application of an approved protective wrapping.
Alternatively a purpose designed friction welded bi-metallic connector offers a quick, easy and reliable method of terminating the copper and aluminium conductors.
Q3.6. If a building has a metal roof, it is necessary to install a roof conductor as well?
Provided the roof is electrically continuous and meets the thickness requirements of BS EN 62305 and is connected to the down conductors, there is no need to install roof conductors.
Q3.7. Can I use the metal cladding around the parapet wall as part of lightning protection?
‘Yes’. Provided the cladding is of sufficient thickness, is electrically continuous and is bonded into the other parts of the lightning protection system. BS EN 62305 gives minimum thickness of sheet metal for this application.
Q3.8. Can down conductors be run inside a building?
A down conductor should preferable run down the outside of a building. If an external route is inadvisable, for example, building of cantilever construction from the first floor upwards should not have their own conductors following the outside contour of the buildings. In these cases down conductors may be housed in non-metallic, non-combustible internal ducts and taken straight to the ground.
Q3.9. How do I route a down conductor in a cantilevered building?
There is no easy answer to this question. Where possible, the down conductors could be sited at the corners where a straight path may be possible, but if as in many buildings, the cantilever continues around the whole building, then natural down conductors could be used, such as the reinforcing bars or steelwork. Or, if the building is in the course of construction, a fire resistant duct could be built in for the down conductor. In any case the possibility of voltage gradients at the earthing positions must be considered.
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.
