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Spuring Sockets and Junction Boxes in Main Bedroom

Postby SRS » Fri Feb 06, 2015 6:59 pm

Hi All.

Am new here and looking for some advice, sorry if the question is a repeat.

I have just started a renovation project, which is quickly spiraling cost wise, so am looking to do some jobs myself.

In the main bedroom there are currently on 2 plug sockets, 1 single and 1 double. They both have 2 sets of wires going in to them which would suggest they are fine for adding spurs to and covered by the rcd at the consumer unit.

The problem I have is that the wiring is already quite bulky before I add the spur wire. Is it possible to run the existing wires to a junction box and then from the junction box to the existing sockets and then create the spur? or is this a big NO NO?

Also, how many spurs is it safe to run from an existing socket? I want to add 2 to 3 double sockets if possible.

Thanks in advance, much appreciated.
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Simply Build It

Postby ericmark » Sat Feb 07, 2015 1:00 pm

There are many ways to extend the ring or add a spur but first you must consider there may have been some one before you who did not know the rules.

So two cables does not mean it's a ring. Job one is test. All power off and all MCB's off you can easy test there is continuity between the three pairs with any simple multi-meter. Once you have confirmed it is a ring then next step.

To extend the ring you should also test the loop impedance to see if the extra length will cause the permitted limits to be exceeded but many DIY people do not worry.

There are two common methods. Using a twin (not double) socket box or using Grid sockets either way you end up with two single sockets one on each end of the ring and you can then use these as points to add the extra cables to extend the ring.

As spurs there are two very different types, Fused and unfused. Using a fused connection unit (FCU) to replace the existing socket you can take the new fused cable to as many sockets as you like. It is just like having a built in extension cable. But without a FCU you are allowed just one device.

Junction boxes have a few problems. The major one is hinged around the safe zones and being able to see it exists the other is use of screw terminals. Screw terminals can with vibrations and heat and cold work lose. So they have to be accessible. There are maintenance free types which use spring clips to hold wires. There are also connector blocks using screws and the Wango connector with uses springs.

The problem where access is limited it is very easy for a cable to jump out as the socket is being put in the box. Clearly if the line or neutral to new socket pops out the socket will not work but on the ring everything will still work but one leg of the ring may be overloaded.

As to earth wires it is all too common to lose an earth as things work anyway.

So once complete you need to test. Be it an easy to access socket to test ring or use of an earth loop impedance tester and compare before and after results it does need testing.

So before you start decide how to test. I often cheat should not say that but if I test the earth loop impedance then open socket then test it is a ring if when I replace the socket I get same reading I am 95% certain I have not got any disconnected wires.

But without having an earth loop impedance tester the only place were you can test wires then replace covers without flexing or bending the wires so you are sure no wires have been disturbed after testing is the consumer unit. However even with the main isolator off there are still live parts in a consumer unit. I am certainly not happy telling any DIY guy to go into the consumer unit.

Only you know your skill and maybe even you don't know? So you have to sit down and decide what route to take. You assess the risk and decide is it worth it.

One option is to do all electrical work then ask an electrician to do an EICR he will not check routes of cables but he should test sockets and use his skill to highlight problems. However by time you pay an electrician to do an EICR then you may as well pay him to do the job.

The problem as I am sure you can see is not doing the job but testing. Job is easy it's the testing which presents the problem. The Martindale EZ150 with loop test will find some but not all faults. The Electrical Safety Council best practice guide 8 a free download does highlight some of the problems.

There are quite a few best practice guides you may want to read some of the others to. The problem is 98% of the time nothing goes wrong. But if your unlucky enough to be in that 2% then it really does go wrong. Emma Shaw, Mary Wherry and Thirza Whittall all died due to errors in the installation. The Emma Shaw case was all about inspecting and testing, the plaster made the fault but the electrical firm failed to detect the fault and as a result the foremen got a jail sentence.

With most of the cases it's not down to one man's mistake but due to a series of errors which all added up together. If some one told me there were sparks and water going everywhere I would say turn off power then the water but at the heat of the moment mistakes are easy. With a broken ring you may have no problems at all for 25 years. Then add one new appliance and fire results.

It is easy for me. One I am not paying and two I have the test equipment required. You however need to assess the risk and decide what to do. As to rules and regulations well they say you must test and must record your results so near every DIY job brakes the rules so the simple answer to near every DIY electrical question of "can I" is "NO" but that's clearly not very helpful.

I can't tell you what to do but I hope I have made the risks more apparent so you can decide what to do.
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