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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Using SWA cable
Planning to bring my garage supply (which has a workshop section) up
to date in Christmas week. (last legal throw before part P) A thread ran a few weeks back on running a supply cable from a house to a (detached) garage & SWA cable was suggested. To take up that suggestion advice is needed as it is a long time since I used SWA cable (& then only once). 1. Rating: It would be buried (as per above thread) about 450mm (18ins) underground (hard drive/path) - about 4m as the crow flies, but 7m-12m after deviations round, up & down. Is it correct to use IEE table 4D1A/ref method 1? (the illustrations for method 1 don't refer specifically to underground use). 2. Ducting: Instead of burying it in bare soil it looks more sensible to run it inside a duct, but attempts to source underground ducting have failed. Does anyone know of a source, or failing that, could semi-flexible 40mm waste pipe be used? If SWA is ducted, how does it affect current rating? 3. Termination: The house end is no problem as that connects into a metal enclosure which I know how to connect, but how do you connect the garage end into a standard plastic consumer unit? Is there a special gland for this? Or do you connect into a service block of some type & then run the last 12 ins or so in tails? 4. Earthing: I'm not completely happy about relying on a non-copper earth (ie the steel armour). Instead can I use 3 core SWA & use the 3rd core as earth to supplement the armour? Common advice seems to be to avoid using the house earth, but if possible I'd like to avoid the work involved in installing an earth rod. The house supply is 100amp PME/TN-C-S. 5. Cable size: nominally 6mmsq cable is adequate for the garage load (ring + freezer radial + lights), but am wondering about using a larger cable - eg 16mmsq. There'd be 2 benefits - much lower volt drop, plus less light flicker when a machine starts. Relative to the whole project the extra cost is small, but are there any practical snags? Does anyone know the outside diameter of these cables? 6. Finally looking up the ratings for these cables in the IEE regs & comparing with the TLC catalog, why the differences? eg TLC show swa 16mmsq 2 core (6942x) as 91amps, IEE table 4D4A shows 89amps. In fact most cable amp values given by TLC are lower than the IEE tables give. Many thanks for all help offered. |
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