DIY Doctor


Postby » Sat May 03, 2008 2:34 pm

Hi...I'm thinking of having my top floor flat re-wired. It was built in 1967, and the electrics have never been looked at. I have an old fuse box, and apparently a 16mm pyro coming up from the meter downstairs. I've had 4 electricians round, and each say different things. Half say I need to bring a new cable from the meter downstairs, which they say is really expensive, whereas the other half say what I have is satisfactory and all that needs doing is just a new fuse box and rewiring the whole flat.

Please can someone tell me what the correct answer is??

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Simply Build It

Postby ericmark » Sat May 03, 2008 6:03 pm

16mm Mineral insulated cable can carry 107 to 137 amp according to installation method. Installation method refers to if it is buried in wall on tray etc. But although it may comply with 17th Edition some supply authorities have their own rules. Many ask for min of 25mm tails but with Mineral insulated cable it can carry much more current for the same size of cable than double insulated PVC cable. I would expect the existing cable would be OK but with so many variables and no report as to why the two electricians say it needs replacing really impossible to answer. Mineral insulated cable is about the best cable you can get and lasts for 100's of years but if damaged or not terminated correctly can absorb water which is the main reason for replacing but without removing the supply one can not really test it is possible electricians are playing safe just in case once the power is turned off and it is tested it is found to be faulty.

Postby sparx » Mon May 05, 2008 10:17 pm

Hi without seeing installation difficult to judge but if not increasing load by a lot then 16mm2 pyro fine.As presume there is some kind of switch-fuse at supply end after meter in which case it is classed as a rising sub-main, then no problem over sizeing.
As long as able to maintain earth continuity with gland then just changing the consumer unit should not be a problem, even using a plastic one if using earth tailed locknuts.
Ensure they bond to other services at your flat not just rely on main bonds downstairs,
Also get test certs & part-p registration in case you ever want to sell!
regards SPARX
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