Fault Find #7

[Paul.M]

Call out to a house, double socket in the far end of the kitchen has stopped working.

Questions to the home owner (my sister in-law btw):-

Has a fuse blown?

"Yes, this afternoon. I re-wired the fuse myself."

Do all the other kitchen sockets work?

"Yes, only the one that we plug the boiler into is broken, now we have no hot water or central heating. (combi gas boiler btw).



I plugged in my MFT into the socket and the readings were:-

L = 0V
N = 244V
CPC = 244V

Now going on what she said and the readings you have, what do you think has happened? Just to help you paint a picture in your mind:- (1) the socket is a spur so only 1 T&E going to it. (2) it has been spurred from another socket and the cpc is not terminated therefore no earth return path.

This is a strange one but it make logical sense once you know the answer.

 

[Dooby]

Oohh! I didn't know you'd been doing fault finding puzzles, how exciting! (am easily pleased, admittedly)
Going to look at the others first

 

[Happy Jack]

L = 0V
N = 244V
CPC = 244V

Thanks Paul, these are always welcome!

Could you clarify the above by introducing each with a reference; live is at 0V in relation to what? N is at 244V in relation to what?

It appears too simple to just assume the socket-outlet has been wired incorrectly. More details are required, I think.

 

[Paul.M]

I took the readings with an MFT and using a plug in adapter box. Each socket pin is tested individually.

Think cable damage in-bertween the two sockets and how can we have 0V on Live (line) and 244V on CPC?

 

[Floody]

Your CPC is giving a reading of 244v yet the earth hasn't been terminated.

My answer: Shes put the live into the earth terminal on accident.

 

[Baker1988]

Im a bit drunk right now so forgive me if this makes no sence, if the cpc is not connected but is giving a voltagethen it must be wired incorrectly and livehas gone in cpc terminal, but thinking about it that cant be right as it must of been wired correctly before or the boiler wouldnt of worked in the first place, its a bit wierd when you say "rewired herself" do you mean it was a 3036 fuse that blue? i think some one has put a shelve up or some thing and damaged the cable with a screw maby or when it short circuited and blew it has damaged the cable and melted it making them touch, are u sure your mft is working correctly and that the socket is not damaged

 

[Happy Jack]

I took the readings with an MFT and using a plug in adapter box. Each socket pin is tested individually.

Think cable damage in-bertween the two sockets and how can we have 0V on Live (line) and 244V on CPC?

Another question, as while this sort of thought-exercise doesn't have any value if you are too explicit, I'm not sure I quite understand you.

So you've metered the socket-outlet, and with reference to 0V you obtained the readings above.

What you describe above, does this still assume you are measuring the socket-outlet and not the conductor itself, having released the face plate from the wall for closer inspection? So this 244V has been measured from where the CPC should be via the pin receptacle, not the actual CPC itself?

The way I see it at this stage, is that only one of the live conductors should have a pd about nominal voltage; the fact that two conductors are at the same voltage indicates a dead-short between actual live and one other, occurring somewhere upstream of the socket in question. And even if the polarity had been reversed, which appears so, I wouldn't always expect that to interrupt operation.

 

[Floody]

Happy Jack, I don't want to sound like a bit of an idiot here, but I struggle reading your posts. Your articulate levels are way above mine, your style of writing makes me need to read your posts 3 or 4 times each just to try and understand it. Your a clever bloke, but for me... You make things more complicated haha.

This isn't an attack on you mate and please don't take offence.

 

[Happy Jack]

This isn't an attack on you mate and please don't take offence.

Haha. No, none taken. I appreciate the honesty.

I've tried to condense what I've written above, but the question remains; I'm not sure I can reduce it any further without attaching a drawing. In fact, I may just go ahead and do that...

 

[Paul.M]

i think some one has put a shelve up or some thing and damaged the cable with a screw maby or when it short circuited and blew it has damaged the cable and melted it making them touch, CORRECT! A simple short circuit due to a floorboard nail that worked its way into the T&E and shorted Live (Line) to CPC making it Live. are u sure your mft is working correctly and that the socket is not damaged

My MFT is less than a year old and I tested it against other socket circuits in the house and then my own house when I got in just to check it. That thought crossed my mind as well.

 

[Paul.M]

What you describe above, does this still assume you are measuring the socket-outlet and not the conductor itself, having released the face plate from the wall for closer inspection? So this 244V has been measured from where the CPC should be via the pin receptacle, not the actual CPC itself? Its an adapter box that you plug into the socket to test the conductors without taking off the plate, its a safe and quick method of fault finding without spending time taking off socket plates that dont need investigating. It also proves dead when switching off the circuit for safe isolation. Once you've bought and adapter box and used it like this or for RCD testing at the furthest point, you will never go back to crock clipping where it is not needed. A by-product of doing this is that you are testing the socket plate as well

The way I see it at this stage, is that only one of the live conductors should have a pd about nominal voltage; the fact that two conductors are at the same voltage indicates a dead-short between actual live and one other, occurring somewhere upstream of the socket in question. And even if the polarity had been reversed, which appears so, I wouldn't always expect that to interrupt operation.

Yes mate, see above for answer. Just a dead short that made the CPC conductor live. Now looking at the "possible" cabl run, it went up stairs into a bedroom with a loose floorboard that over time a nail punched its way into the T&E. Floorboard up, cable repaired using MF Wago's and a choc box, tested and job done.

This was a can of worms that I've opened! Once I took the front off the C/U a whole load of problems came my way. 6mm shower and a 6mm electric cooker + a socket (in 2.5mm) was all on the same 30A BS3036 fuse!!!! I found 4 circuits that were redundant but still terminated to the board??? Ripped them out for a start. The whole house lighting on one 6A fuse. 2.5mm radial skt circuit on a 30A! So I spent my Sunday ripping the lot out and putting in a nice new shiny 10 way split RCD board and chasing borrowed neutrals, all free of charge for my sister in-law. Should have cost close to £400! Her husband is a bit of a mechanic and he will be doing work on my van free of charge, trust me

 

[Baker1988]

My MFT is less than a year old and I tested it against other socket circuits in the house and then my own house when I got in just to check it. That thought crossed my mind as well.

"correct" thats what i like to hear haha

 

[Happy Jack]

Yes mate, see above for answer.

Thanks for that Paul. I had envisaged a R1 + R2 plug top tester, like the one Kewtech make and that I link to below. From your description it doesn't sound like the product, so can you provide a link to the one you used, for clarity?

Kewcheck R2 Socket Adaptor - R2 - Test Without Removing Wall Socket

Her husband is a bit of a mechanic and he will be doing work on my van free of charge, trust me

From what you describe I would hope so! And always nice to see the trades exchange in this way.

You find any more 'faults' Paul, please do let us know!

 

[Paul.M]

That's the one but mine is the previous model. I've also got a full set of light mates, worth their weight in gold when your up a ladder with 3 leads and a box around your neck.

 

[KWCFC]

Hi Paul. If there was a short between Line and Earth why had the Breaker/fuses not tripped? From what I gather the socket wasnt working but the circuit was still live?