I am due to fit a socket in a staff room kitchen which is simple enough. The only problem is that there only appears to be one DP socket and a spur attached to it. I'm assuming this must be a radial but frustratingly for me it is not listed on the Diistribution board. The cables are 2.5mm so it is either a ring or a radial but I''m cautious to add a socket to this existing arrangement as the existing socket already has a spur. There are no other sockets within at least a 20m radius. Any ideas?
In theory if you took 8 spurs from a ring main at the same point it would be no more loading than 8 spurs one on each of 8 existing sockets of a ring main (Although may be not to regulations) but in practice getting four 2.5mmÂ² cables into one hole in a socket is near impossible. One way around this problem may be to change the double socket for two singles ring going in one out of other so with two spurs still only three cables into each socket. Although in domestic ring mains are common in commercial radials seem to be preferred method often in 4mmÂ² on a 30 â€“ 32 amp supply and I have seen where electricians have assumed it is a ring main and used 2.5mmÂ² to extend instead of 4mmÂ² plus of course the volt drop can easily become excessive. Always check the R1 + R2 etc. Easy on a ring Line to Line at 4% and 32 amp <= 0.29 ohms so one measurement shows if it is ring and if you can add to it keeping within volt drop. On a radial you need to find last socket. I sometimes use 230/PSC line to neutral at last socket (= total ohms to supply transformer) â€“ 230/PSC at board = R1/2 but unless you understand keep to method your happy with. Some ELI and PSC meters measure only PSC line to earth and donâ€™t have a switch to check line to neutral and would take longer to make test leads than measure with low ohms ohmmeter. I am assuming youâ€™re an electrician and this is being done at work other wise it would be over the head of most DIY people. And to make out minor works cert you will need meters anyway remember as last person to work on the circuit you will be responsible for the whole circuit so testing is very important to show not only any mistakes you may make but those which may have been made in the past including if the sockets on the circuit could be used to power things outside that there is RCD protection or if missing it is noted on paperwork. i.e. watch your back.
I had assumed you were a maintainance electrician. I have had the same problems myself. Unlike the domestic guy who inspects and tests every day you may only be required to do it once in a blue moon and often you find a lack of test equipment where most installation work is out sourced. These outside firms love to point it out when someone before them got it wrong. Which is why I said watch your back. I have gone to management many times and said to do this job I will need xyz and it may be cheaper to out source. If you have done same job before use the "There are new regulations and now I need xyz." No shame is saying there are new regulations and I need the books and get firm to buy BS7671:2008 and new book 3 and guild to 17th Edition. With new regs out and in force July 1st this is right time to ask.
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