Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, about exterior uplighters and the cable to be used to supply them, is answered by BASEC:
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| H05RN-F rubber cable - limited protection against digging. |
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Question: I am installing some flush fitting external uplights (Class 1) for a commercial development. The client has sourced the uplights from a supplier, which claims that I can use
H05RN-F rubber cable. Surely this cannot be correct, can it? What type of cable, other than SWA - if any - can be used? Guardian? I will have a problem - not uncommon - that SWA cable is just not designed for termination into these fittings. Please advise...
Answer: Buried cables should have mechanical protection such as SWA or conduit.
Buried cables should have mechanical protection of some form if digging is possible in the area where they are installed. If the lights are mounted in areas where digging is not likely, such as in concrete or a pathway, it might be argued that this is sufficient protection from digging.
The commonly specified cable in the UK for protection against digging is a steel wire armoured (SWA) type such as BS 5467.
Screened cable made to BS 8436, such as the Guardian product you mention, is not intended for outdoor buried use as it does not offer sufficient mechanical protection.
Rubber sheathed cable, such as H05RN-F, is a rugged type of flexible cable suitable for outdoor use, but it offers only limited mechanical protection against digging.
Manufacturers of ground-mounted or buried electrical products, such as exterior uplighters, should preferably provide the ability to properly terminate SWA cables so that earth continuity is maintained. If the terminations cannot be made effectively (electrically and waterproof), then either an alternative light should be used, or other methods of protection of cables used (such as steel conduit).
Dr Jeremy Hodge, BASEC
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