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.

 

[mackers]

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 ?

the hills are ALIVE with the sound of music or maybe not in jimfuego's case!

 

[Des 56]

I am going to apologise to jimfuego for my tasteless humour

jim, Have this thread back

Humour leads me astray I'm sorry to admit

Now tell us, what is the answer to the mcb issue ?

 

[RWJ]

I am going to apologise to jimfuego for my tasteless humour

jim, Have this thread back

Humour leads me astray I'm sorry to admit

Now tell us, what is the answer to the mcb issue ?

I'll carry on playing chequed flag on this online speccy emulator..... I'm 6 years old at the moment!!! Stuff my 6 year old's NFS on PS3 rubbish he don't know a decent driving sim!!

 

[Side Cutters]

If you've already checked each accessory and switch, disconnect at each point and do a continuity test to find the damaged cable or connection.



I am 17 turning to 18. Was that a song in the sound of music?

 

[1shortcircuit]

which could obviously be virtually impossible to find - especially as the customer has recently insulated the loft and and boarded over part of it.

It seems there are a few discrepencies that need to be attended to before further advice can be given. Your results are showing a fault on line and neutral conductors but no answer has been given to suggest that lamps, transformer packs or even dimmer switches have been removed from the circuit.

The other point I will address is the "Virtually impossible to find"??? Why is it? DIVIDE and CONQUER! You will find which accessories the fault is between, if you do not have access then explain to the customer that gaining access to continue your fault finding will still be charged at your hourly rate, when I suggested this to one of my clients they were in the loft like a ferret moving insulation and boards in order to assist (genuine customer though and probably quite rare these days):thumbsup

 

[Edd]

Hi chaps/chapesses

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 your getting 0.0M ohm L-N and the MCB is still on!! then its one of three things.. either a lamps in circuit still and your testing through that,(this will give the reading but wont answer why no supply) or the cable really has gone down.(this would give the reading but also trip the mcb) or a failed MCB. (open circuit when in the on position) Im guessing dodgy MCB and lamp in circuit..
Good Luck.

doe a deer a female deer, ray a drop of golden sun!!
sorry its in my head ile go stand over here....

 

[trev]

I'm really surprised no one has mentioned Edelweiss yet.

 

[telectrix]

eric weiss was the real name of houdini. are they related?

 

[mackers]

eric weiss was the real name of houdini. are they related?

get out of that one trev!LOL
you may have to press the"esc button"

 

[trev]

They were brother and sister mate but one of them was adopted
esc, esc, esc, nope that's not working. I'd best reboot

 

[jimfuego]

Morning chaps

Apologies for not replying sooner - having posted late on a Saturday night, i didn't think i'd get any replies til this morning!

So - a): i did check the voltage coming out of the MCB (with a voltage tester :wink_smile and it was reading 240V - a faulty MCB was my first suspect - but no voltage at accessories.

b) the customer stated that when he boarded out the loft he raised the finished floor level up by using 2x4 struts on top of the joists, and that he worked round any cables he encountered. i can see that he has raised the floor and i trust him on the cables (he's a builder).

c)
schoolboy error on the insulation resistance: took all the bulbs out on the circuit, but now you mention it forgot to isolate the transformer pack for the shower light...

d) 1shortcircuit: "The other point I will address is the "Virtually impossible to find"??? Why is it? DIVIDE and CONQUER! You will find which accessories the fault is between," " & sidecutters: "If you've already checked each accessory and switch, disconnect at each point and do a continuity test to find the damaged cable or connection." - this is what i had started to do before it got dark yesterday and which i will continue to do to try and pintpoint the faulty bit - so you're right: not 'virtually impossible'.

i was just a bit worried that after 90mins work i had no answers for the customer, so was just asking the question on here to see if anyone had any suggestions - so thanks for all the responses.

Going forward, i'll double-check the MCB and carry on with the continuity testing - whistling "The Sound of Music" as i do so...

cheers

 

[Edd]

If you say that there is a supply leaving the MCB but nothing at the lights, then its really gota be at the first on the circuit, or the cable run from CU up to first point!!
again good luck..
PS dont leave us all hanging when you do find the fault, theres nothing worce than reading all the advice then never hearing what the out come is..

 

[trev]

Going forward, i'll double-check the MCB and carry on with the continuity testing - whistling "The Sound of Music" as i do so...

cheers

That'll be how you solve the problem, like Maria.

How long can we get away with references to the sound of music before we get shouted at for going off topic?

 

[telectrix]

well, julie had her gestapo, we've got moderators ( sorry, mods, only joking):furious3:

 

[kung]

If you say that there is a supply leaving the MCB but nothing at the lights, then its really gota be at the first on the circuit, or the cable run from CU up to first point!!
QUOTE]

Thats where id be checking ! also could redo connections as its like the pencil lead it could have a break even though it looks ok ! discon from cu and test at closest light on circuit i recon to.

 

[jimfuego]

If you say that there is a supply leaving the MCB but nothing at the lights, then its really gota be at the first on the circuit, or the cable run from CU up to first point!!
again good luck..
PS dont leave us all hanging when you do find the fault, theres nothing worce than reading all the advice then never hearing what the out come is..

thanks Edd - i'm hoping it doesn't take long to identify

 

[kung]

For quickness lash up a jump wire as a last resort if lights fading and safe to do ! while replacing cable if needed ! can also work with socket circuits.

 

[ezzzekiel]

as everything has been covered i would just add as a recomendation to your client to use candlelight (very easy to rectify faults and no part p to worry about)