Electrical Fault - Correct Diagnosis?

Hello,
Just noticed that electric boiler in out flat didn't appear to be
heating any water. The fault was quickly traced to the DP switch
supplying power to the heating element, which would no longer physically
switch from the on position, and which no longer had the neon light
illuminated.
Examination of the back of the switch showed significant charring at the
top of the dry-lining box, on the back of the switch where it had been
pressed up against the neutral wire, and about 1 inch of the insulation
from the neutral wire had burnt away, leaving significantly discoloured
copper underneath. The other wires looked largerly unaffected.
Finally, the neutral wire was loose in its terminal on the switch.
My conclusion would be the original installer either hadn't tightened
the neutral terminal, or had tightened it onto the neutral wire's
insulation, leading to very poor contact, and the consequent arcing
which overheated the neutral wire and damaged the switch.
Firstly, does this sound like the correct diagnosis?
Secondly, how cross ought I to be with the builders / developer. Would
you consider such wiring as grossly incompetent and as having come close
to starting a fire, or just as slightly sloppy and of no real danger?
Does it seem unreasonable to demand a full wiring inspection to ensure
that there aren't any similar issues lurking elsewhere (New build flat,
completed just over a year ago)?
Many Thanks,
Reply to
Christopher Key
Diagnosis sounds OK (I'd bet on slack screw), just had a similar failure myself in a metal box after about five years. I guess drywall boxes are pvc or some other fire resistant plastic, so not a large fire risk. If arcing or overheating gets beyond a certain point usually an ELCB trips and the "fire" goes out. My gut feeling is that 95% of such faults are fail safe (perhaps someone in the trade has some statistics?). Of course this isn't to say that electrical faults don't sometimes cause serious fires, but I suspect the problems arise when there are wood shavings or a mouse nest or similar in the wrong place, or a non-compliant bundle of wires. This is another advantage of all-metal boxes and metal conduit as used in schools / hospitals / factories.
Reply to
newshound
In article , Christopher Key writes:
It's quite likely if it's a recent installation. If it's not recent, then I would say slightly more likely, particularly if it's a cheap make of switch, is that the switch contacts have gone high resistance, generated excess heat which is conducted back to the screw terminal. This might result in the screw terminal failing too when it overheats, or it could just be suffering directly from conducted heat.
Replace the switch with a good make such as MK, and not the cheapest on the shelf. Check tightness of the other terminals on the circuit.
For a one-off, I would forget it and move on.
Reply to
Andrew Gabriel
In article ,
Yes. Inadequate tightening is pretty common. Dunno why. Perhaps just using a screwdriver that's too small. It's near impossible to overtighten them without employing a gorilla.
The whole idea of a backing box is that it will contain any fire.
I'd first remove a couple of random sockets and check if the screws are loose.
Reply to
Dave Plowman (News)
You would be surprised how often I find this. Light switches, sockets, DP shower switches, ceiling roses. Very common fault.
My Dad always taught me to 'tighten it up till it squeaks' which I still do today.
Reply to
The Medway Handyman
Tighten, push accessory fully into place on back box, gently pull forwards and tighten again. Cables often move slightly as the accessory is moved into place, however tight you did the screws up first time.
And always try and pull the cables out to test if tight.
Reply to
rrh
Instead of a few random sockets, you could test all the sockets at once by doing a continuity check on the final ring.
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says that whichever of the live/neutral/earth readings is high will only be found by removing and tightening up the terminals on the last remaining socket you have to check and this socket will also be in the most inconvenient place.
A simple work around to the above is to start with the most inconvenient socket and this time the problem socket will be the easiest one to access. It will still be the last one on the ring circuit that you have to check though.
Adam
Reply to
ARWadworth
Tighten, waggle the wire to settle it in, then tighten again - finally give the wire a tug just to make absolutely sure.
Reply to
Harry Bloomfield
In article ,
Just a question of using the correct screwdriver. Many seem to think a 'mains tester' ideal for such work - they're not. You need a decent one with a shaft the same diameter as the screw head (as a rough guide).
Reply to
Dave Plowman (News)

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