Dead Circuit

[jimfuego]

Hi chaps/chapesses

I have been looking at an upstairs lighting circuit today: a bulb blew this morning (the MCB didn't trip) and subsequently the whole circuit stopped working. The MCB was stil closed when i arrived and no voltage or current was present at the accessory or either of the two way switches. I've checked the connections in all the switches/accessories/visible junction boxes in the loft - and at the MCB - and they're all tight and can see no obvious breaks/nicks/pinches at these points. I'm getting continuity readings on all conductors at the point where the bulb blew (slightly high on line and neutral). I have also done an Insulation Resistance test on the circuit and am getting a reading of 0.00Mohms on L/N, and about 4Mohms on L/E and N/E.

The only thing i can think of is that the basic insulation has failed somewhere in the circuit, which could obviously be virtually impossible to find - especially as the customer has recently insulated the loft and and boarded over part of it. (could too-thick loft insulation cause 1mm cable to heat up so far as to melt? there are only 6 points on the circuit).

does anyone have any other ideas of what it could be, or are we looking at re-wire?

any thoughts appreciated

cheers

 

[mackers]

was there any voltage on out going side of mcb?

 

[needasparks]

Might sound obvious but is there power actually coming out of mcb ? It could have failed during the fault.

 

[RWJ]

was there any voltage on out going side of mcb?

Not using a Neon screwdriver!!!!! A proper voltage tester if you can

 

[needasparks]

snap.......

 

[Des 56]

Thank you lads
Minds with the same thought as me but much quicker with the keyboard rendered my ramblings old hat

Because I went to the trouble of pounding the keyboard,I'm posting it

I will ask the silly question, just to get the missing info out of the way

Was a supply confirmed at the load of the mcb ?

 

[Marvo]

I'm getting continuity readings on all conductors at the point where the bulb blew (slightly high on line and neutral). I have also done an Insulation Resistance test on the circuit and am getting a reading of 0.00Mohms on L/N, and about 4Mohms on L/E and N/E.

If you belled out all the wiring and your IR test is 4M then the wiring is okay. I'm guessing there were still lamps in the fittings which gave you the '0.00Mohms on L/N'

The only thing i can think of is that the basic insulation has failed somewhere in the circuit, which could obviously be virtually impossible to find

Why do you say that if your IR readings were okay?

could too-thick loft insulation cause 1mm cable to heat up so far as to melt? there are only 6 points on the circuit).

Anything's possible....... but you would have seen it in the test results.......

.....or are we looking at re-wire?

A rewire on what grounds?


What type of lighting is it?

 

[mackers]

0.00 megs just a thought did you take the lamps out?

 

[Side Cutters]

Did the people that boarded out the loft put a screw partly through a cable?

 

[needasparks]

when i started out every fault i went to i emptied the van of tools and testers, I then learned to start at the begining and think basic.
Never let me down yet. You can get bogged down with the things the fault has caused and miss the obvious. Good luck fella.

 

[mackers]

yep, always start at the very begining, a very good place to start,!

 

[RWJ]

^^^^ Julie Andrews

 

[mackers]

^^^^ julie andrews

doh, ra,me ! Name that tune in one!

 

[Des 56]

when i started out every fault i went to i emptied the van of tools and testers, I then learned to start at the begining and think basic.
Never let me down yet. You can get bogged down with the things the fault has caused and miss the obvious. Good luck fella.

Lets carry on that excellent piece of advise and start the ball rolling (assuming getting replies off jimfuego)

Quest 1 ( in my best July Andrews tone )

Was there a shilling in the meter ?

 

[needasparks]

I had an old boy i was working for. he would watch me running in and out with tools while sitting there rolling a smoke.
then when i had finished he would look up and say ''You checked the fuse boy! '' learnt real quick.