I have come across this in the past where over the years there have been re-wires without removing the old cables.
I have found one can get some sort of idea as to what feeds what by measuring the loop impedance where there is a ring as one leaves the fuse box one sees the impedance raise the fall as one returns to the fuse box with large jumps for those sockets on spurs. Not the correct way but it gives one a quick indication and also tells one if you could convert to MCB's.
The problem with a MCB is it's not a continuous as with the fuse but has a straight line where the magnetic part takes over from the thermal part so there is a very defined point of pass or fail on the loop impedance.
Testing the ring exists for all that's line, neutral and earth is of course important and the correct method is to create a loop and then with a low ohm meter test the resistance and all sockets which are part of the ring will have the same reading. However going to all that work is rather pointless if the loop impedance will not pass anyway.
The MCB as I said has too distinct parts the thermal bit will cause it to eventually trip at the rated current but this could take hours. The magnetic part will ensure it will trip within the time allowed with a short circuit but with a short circuit the current needs to be 5, 10, or 20 times the rated value for a B, C or D type MCB. So for example a B32 MCB will need 160 amps to flow to trip it which equates to a loop impedance of 1.44 ohms. With a fuse being slightly over 1.15 ohms for a BS 1361 30 amp fuse will just mean it takes slightly longer. But with a MCB being over the 1.44 limit means it could take many times longer as it needs to heat up the thermal part instead to the magnetic bit working.
Once you have the data then you can decide the best way forward but without the data guessing is just not good enough.
For the DIY man the first consideration has to be is it worth buying or hiring the test gear? The loop tester, low and high ohm ohmmeter and the RCD tester which also records the time taken to trip will as a set cost around £750 to buy or £75 to hire. Normally min of one week to hire. So you would need to work fast to complete all work within the week.
As for the professional there is the problem in leaving work not deemed as safe. One is not permitted to leave a house uninhabitable without finding alternative accommodation but also one can't re-energise a circuit deemed as dangerous and in the world of blame that gives the electrician a real problem. To complete the tests he has to switch off the power and if he then finds a fault he can't re-energise however neither can he lock it off so once out the door you could re-energise. However once you know it's dangerous then to re-energise should some one be injured you would be libel.
It's that sucking through teeth and jobs worth comment. So if you think it will fail then to get an electrician to tell you what you already know is rather pointless.
So the next best is the socket tester with a loop tester built in. There are two popular types one by socket & see and the other by Martindale both just over £50 the SOK34 or SOK36 or EZ150 these are not as good as the loop tester used by the pros but do a reasonable job I would expect the EZ150 would likely be best for you. Try Test4less they seem to have low prices.
However at £44.16 plus vat still not cheap. By time you have bought or hired the test gear one wonders if it's really worth DIY?
The
http://www.esc.org.uk/industry/industry ... ce-guides/ Number 8 does tell you some of the problems with using socket testers. Have a read then say if we can help.
