MCB tripping after a couple of minutes

  • Thread starter Thread starter GeX
  • Start date Start date
GeX said:
What I think is the feed for dining room light is showing ~22v between live and neutral. I'm not sure why that'd be. I'm perfectly at home debugging electronics / PCBs with my trusty multimeter..

It's back to not tripping the MCB, but the dining room and porch lights not working.
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This tells you the fault is between the last working light or the first light that doesn't work - either at the connections at either light or the cable between them

22v with the mcb on or off - if off it will just be induced voltage from other cables running alongside

Whats the reading between earth and live and earth and neutral - then assuming the earth isn't broken you can tell if the live or neutral cable is broken

if you have 230v L to E, but not 230v L to N then neutral is broken
If you have don't have 230v to either N or E and have continuity N-E then L is broken

Probably a L - E short that now has blown itself apart and cleared the fault and broken the connection to dining room and porch lights
 
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GeX said:
What I think is the feed for dining room light is showing ~22v between live and neutral.
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daft question - how do you measure that, if the mcb has cut the supply .. or do you mean a resistance measurement of some kind.

to rule out the switch->bulb wire short, did you remove all bulbs and disconnect switch on one side, in case they too, have a fault.

but further than that, if you cannot see wire defect, don't you have to break the ring at judicious/bisection points and see if you can observe L/N shorts with a multimeter

did you find a good online guide ?
 
ok, hopefully tonight I can get the PIR / porch light apart and see if that's looking suspect.

The thing that is throwing me is the fault seeming to change - but also that the between the dining room and porch is the hallway - and those lights are working.

I've removed old, dead cables that were left in from the rewire and will take another look later and hopefully trace the wiring back.
 
It'll be pressure fault on a cable. Guarantee it.

Get an Electronian out. They'll have that diagnosed and fixed in a couple of hours and it'll not cost you a lot.

Source: Electrician.
 
This is sorted now. Turned out to be two faults.

There was a terminal block out of sight that the earth had come out of, and was alarming close to poking the live. This is what was causing the breaker to trip when cables were moved around. The porch and dining room lights not working was because they'd borrowed a neutral from the lounge circuit. The lounge has recently been redecorated and had a plaster ceiling rose fitted, the decorators didn't refit the light fitting as the paint wasn't dry. They also didn't join the neutrals for it either.

Electrician also checked the cables for any crushing damage, nothing seen. In the photos all of the squished ones through notches are actually dead.
 
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