Think Everyone Should Take a Look at this one

[pipdark16]

Hi Guys, First time ive posted on here but could do with a few opinions.

I've just been called back to a rewire I recently completed for a faulty bathroom light fitting. When diagnosing the fault i just so happened to put my fluke volt detector stick up against the concrete block wall and it alarmed showing voltage present. Bare in mind that this voltage tester only alarms at 200 volts and above and if anything, is under sensitive for my liking. Moving it across the wall i have found most of the wall to be showing live. Nice...
The only thing running through the wall is my cables and possibly some metal ties in the block work. All my tests came back well within limits upon commissioning but decided all it could be was those cables. I therefore disconnected them and performed an ins res test between all conductors. All came back >299M ohm using a megger MFT1553 that is nearly brand new. If someone put a nail in that wall then that nail could become live, no? As i came about this purely by chance i am wondering where us sparks would stand, should someone be hurt, as there are no tests that could show this.

Any response would be good guys

Cheers

 

[electricAl]

Its very late (my backs stopping me from sleeping) so excuses if this post makes little sense but

If you`re asking whether its your responsibility to ensure all the walls of the property are not live, then call me negligent but its really not something i usually check

Sounds as if you`ve fallen unlucky, but in case you have inadvertently had a hand in this, a couple of things spring to mind

Firstly, as you say the wall is blockwork in a bathroom, i`d have thought it a distinct possibilty that foil backed plasterboard may have been used (AquaPanel or similiar) If that is the case the mind drifts to possible causes of PD to earth - an faulting accessory or even pipework contacting it perhaps? altho quite how it`d become live without operating the protective devices - & you`ll have fitted RCDs to each cct.
From your description it doesn`t seem likely that any metal work would exist within the wall - no studs? - but remote possibility of a Catnic being within the wall for some reason? The rebars of a lintil maybe?
Is it a party wall? Conceivable the fault originates next door, or even on an outer wall, altho i`ll admit it seems unlikely.
Even less likely is someones Main running thru the wall.
And as all these possibillities would require your Megger to be up the duff at the very same time...extremely unlikely

In fact, they all seem unlikely. Thing is of course, even the most unlikely things happen from time to time...

 

[Griffin]

Hi,

I have had a similar situation a few years ago ( not in a new installation though)

I was called to an old cottage where the plasters were reskimming a wall and were moaning about getting a shock. (they are always moaning about something)

Further investigation proved that there was no earth to the lighting on that wall, there was a cpc but there was no continuity back to the board.

After ripping up a few upstairs boards found a lighting JB where the earth had come out of the terminal?? Must have been like it for years

Reconnected it.... floating voltage gone

Hope this helps

G

 

[Mr Mark Sparks]

strange!!!!!
you say most of the wall shows live
what is causing the wall to be conductive if you put a megger on the wall at 500v with the leads say 1m apart do you get a short??

 

[pipdark16]

Thanks for the replies guys. Didn't think about foil backed board but can't say I've noticed any during the install. Obviously whatever metal work it may be isn't, and in my opinion cannot be, effectively earthed. No RCD trips nothing. And the wall only shows live with my volt stick(non contact). Don't particularly want to stick something in it to see what happens. I've Checked all my wiring in JB/Lights/Switches ETC. All fine. I mean, say unsuspecting kiddie runs along and sticks a fork in the wall (which these kids are likely to do). Does my RCD still protect them/me effectively? As I said where would I stand in the eyes of the law as I have carried out all required tests and issued relevant certs. heck even had the council in for the building regs and had my part P assessment on the place. Think im going to open up the cable track where I pulled the cable through the original capping, which was tight, and see if ive chafe one conductor, on one side of the 3 core for two way lighting. Sound like the right move?

 

[Yooj]

Hi,

Isolate the dwelling supply...does the voltstick still show a voltage present?

Furthermore, can the voltstick be relied upon? Is it just saying that there are some live conductors somewhere within the wall, rather than the wall itself being live? I myself do not use voltsticks, and therefore I am unsure of their capabilities.

Get a wander lead, bang a large screwdriver into a flower bed in the garden as a temprorary earth-rod and measure the PD between it and the wall. Do the same between the screwdriver and the MET and the MET and the wall. This might shed some light on things...

Yooj

 

[old dog]

isolate the circuits one by one this will narrow it down. had something like this a few years ago
volt stick lighting up on the wall. found it was on the down stairs ring . split the ring found the leg between
2 sockets that was causing it and replaced it. never got to look at the cable its still in the wall and made safe
oh and all the readings i took would not pick it up

 

[Gravid]

Good old trusty voltsticks !! Chuck it in the bin mate.

 

[ian.settle1]

Good old trusty voltsticks !! Chuck it in the bin mate.

Not classified as an Approved Voltage Indicator anyway.

You used that to prove a circuit was dead and then you had an acciedent and HSE came calling expect a big fine at the end of the prosecution.

 

[pennywise]

Volt sticks are useless I got a false voltage indication from rock wool of all things. Think your phantom fault may be down to the volt stick.

 

[Romans99]

When the batteries are running out on the volt sticks they give dodgy readings.

Instead of it being something really bizarre or dangerous Im thinking the problem is the volt stick.

They are handy little things but looking at the price and the technology involved (or lack of) they can't be relied upon as a serious piece of testing equipment.

When working on outside lights that are wet/damp, mine shows live all the time even though I've tested for dead.

 

[pipdark16]

If the lighting circuits are isolated the voltage doesn't show. Think it has to be the cable but will try changing the batteries and see if i get the same. Will also try a different stick. My point still remains that if i put it down to the voltage stick and leave it, and there is live metal work in the wall, the day someone hits it, i'm in the s***...No?

 

[steamboatwilly]

If the lighting circuits are isolated the voltage doesn't show. Think it has to be the cable but will try changing the batteries and see if i get the same. Will also try a different stick. My point still remains that if i put it down to the voltage stick and leave it, and there is live metal work in the wall, the day someone hits it, i'm in the s***...No?

Absolutely, it's important to work out whether it's the volt stick or the wall. I use a variety of volt sticks when I've isolated circuits (etc) just to treble-check that the conductors are not live on the section I'm working on. Belt and braces I know. However, point is that they all light up every now and then depending on the material or whether they've been lightly 'banged' (something normally reserved for a Friday night after the pub ).

As the guys say above, turn circuits off one by one and try to narrow it down. Find a method of measuring voltage other than the stick.