In need of a fault finding wizard

[Sparky Ninja]

What I do know is that if I was the OP I would be thankful for all these ideas, but probably scratching my head with where to start next....

 

[Kamikaze]

This has the hallmark of a damaged cable. Something like a screw through a T &E cable or a nail through the sheathing into a T & E cable. The most sensible thing to do is to disconnect all connections on this circuit and systematically work your way through each leg. Insulation resistance and continuity tests. I know this is time consuming, but the real headache will be when you find it. Replacing the cable, now that everything is probably plastered and decorated.

 

[IQ Electrical]

I'm sure the OP said he'd done IR tests, that would surely have indicated a fault of sufficient magnitude to 'leak' 42 Volts.

 

[Sparky Ninja]

Hi,im in need of some help.Recently completed a 80 bed nursing home,its been tested and the whole installation is electrically sound bar one thing,i got a really puzzling fault on a lighting circuit protected by a b6 60898 .when the circuit is switched off the lights dim(18w pl lamps)after days of testing procedures r1+r2 insulation r and zs all fine ,the voltage is 42v between cpc and line any help please

I'm sure the OP said he'd done IR tests, that would surely have indicated a fault of sufficient magnitude to 'leak' 42 Volts.

I think so too.

I still think the first thing to do is locate the circuit creating the problem via a method like I suggested. Then when the circuit is found, dissect the crap out of it.

 

[bugsy]

I think the problem is more than likely to be a neutal or switch line fault , what cables are installed (skinned , singles , fp. armour?

 

[whats an rb4]

i agree with widdler on this one induced voltages are always a worry but unlikley dont tjhink property wolud be large enough for this to come into play

 

[cr_sparky]

i have had 42v at a light switch before in a old building,there was a neutral (red single core)connected in the line terminal,with it being an em light circuit (3 core) maybe you have got incorrect polarity?

 

[WDMDL]

OK.. you've done IR tests on that circuit...

the problem circuit is 5 wall lights controlled via photocell and timeclock.simplest circuit in the building typical.many thanks

Timeclock AND photocell? Why? Do you need the lights to go off after a certain time of night?

Is the photocell the NEMA socket type?
Check that is specified as a relay switched type.
If not, these need to pass a small amount of current all the time to power the internal circuit. But generally they will say "suitable for filament lamps only" if this is the case.
Unplug the photocell, see what happens

Same with the timeclock, check that it is a relay switched type too. (listen for the relay click as you operate the override)

But if it's induced voltage that's the problem (sounds very unlikely now), and the luminaires don't have PFC correction capacitors, fitting them will generally pull the induced voltage right down.

Simon.

 

[Doug]

If there is still a voltage present when the circuit is switched off at the MCB then perhaps the MCB is faulty.

This has the hallmark of a damaged cable. Something like a screw through a T &E cable or a nail through the sheathing into a T & E cable. The most sensible thing to do is to disconnect all connections on this circuit and systematically work your way through each leg. Insulation resistance and continuity tests. I know this is time consuming, but the real headache will be when you find it. Replacing the cable, now that everything is probably plastered and decorated.

A link between this circuit and another should show on IR tests between circuits. Alternatively, switch off every circuit except this and look for a voltage on another circuit.

 

[the pict]

move the line to another breaker ? MCB's can sneak voltage past the contacts
Pict

 

[IQ Electrical]

hi des,thanks for reply if it was a main earth problem why only that circuit with the fault out of so many.i have disconnected all the accessories off this circiut and removed the line at board but when i test voltage between the so called dead live and the earth bar it still shows 42v how is this pos.ive also checked all ceiling grid and metal stud for voltage and its all clear.

I think he covered that.