Is this a switch in the neutral instead of the live?

[Davisonp]

I had an odd one today.

I was investigating a problem with a light that was not working. As it turns out, it was multiple loose connections causing the problem.

The circuit is wired in old unearthed two core cables making the contact voltage tester a waste of time.

At the light fitting there is a single two core black and red cable appearing and connecting into the ceiling rose, however, a non contact voltage detector indicates that there is constant voltage on the black cable regardless of the switch position. This black cable is connected to the pendent neutral.

The light switch is a double switch and both switches have a two core cable to each switch. The non contact voltage detector does not detect any voltage at the switch unless the light controlled by that switch is turned on and working.

I was surprised that the non contact voltage detector only detects voltage at the switches when the light controlled by that switch is illuminated. The switch controlling a compact florescent lamp does not surprise me too much, but the second switch controls halogen bulbs, so I would expect there to be voltage potential at the light switch even if the switch is in the neutral cable and the switch has the lights off.


I am pretty sure both lights have the switch in the neutral. Can anyone confirm my theory, and why there appears to be no voltage at the switch when the halogen lights are turned off.

 

[Pete999]

Don#t use a Non contact voltage indicator to trace faults or problems.

 

[telectrix]

as pete says, these voltsticks can pick up stray voltages all over the place and cannot be relied on except as a rough guide. test circuits as per taught using approved testers.

 

[hightower]

as pete says, these voltsticks can pick up stray voltages all over the place and cannot be relied on except as a rough guide. test circuits as per taught using approved testers.

Difficult to test using two probe type when all you have is a line and a switch line at the box. Time to invest in a single probe voltage tester?

 

[Rosco]

Rub a Voltstick on your fleece and you could be fault finding for years lol

 

[buzzlightyear]

voltsticks to inducate magnetic force.

 

[Pete999]

voltsticks to inducate magnetic force.

voltsticks to inducate magnetic force.

Inducate WTF is inducate

 

[Dave OCD]

If the switch was connected across neutrals surely you'd have mains potential on one side of the switch when off -an open neutral ?

 

[Davisonp]

Don#t use a Non contact voltage indicator to trace faults or problems.

Initial investigation was with a contact voltage tester, that confirmed there was no voltage whatsoever at the switch, and when testing the ceiling rose, no voltage between live and neutral regardless of the switch position.

My contact voltage tester beeps a warning if you touch anything with live potential, but will only display the voltage when you touch the other prong to an earth or neutral, somewhere creating a potential, and the tester also has a constant tone to indicate continuity. So, no power detected anywhere by the touch voltage tester.

So, on the working light switch, the contact detector gives no voltage or potential between the two cables with the switch in the open position, then the tester reports continuity when the switch is closed and the light is on and power must be running through the switch, so why does the touch tester not beep to tell me there is AC?, unless the continuity test overrides the AC warning in this situation, and yes, the tester is working correctly as confirmed with both the test box I carry and self the internal self testing.

So, I moved to the contactless tester as a tool.

Nothing identified at either switch until the working light turned on then power detected on both the switch cables for that light, but nothing detected on the other switch wires, it was then that one of the leads popped out of the non working light switch and I found all four connectors were loose.

Tightening the switch connectors and the light still did not work.

So, back to the ceiling rose, and the non contact voltage detector could not detect anything in the red cable, but it did indicate voltage on the black cable, regardless of the switch position.

So, why does the contact voltage detector not find voltage in the neutral area of the ceiling rose, It is because the black cable was also loose, and not connecting with the neutral bar of the ceiling rose, but visually appeared to be fine. The non contact tester could detect the voltage.

Reconnecting the black cable and tightening the connections on the ceiling rose, and the light works again.

So, the question is why is there no voltage at the switch? Is my suspicion of a switch in the neutral correct?

 

[Davisonp]

as pete says, these voltsticks can pick up stray voltages all over the place and cannot be relied on except as a rough guide. test circuits as per taught using approved testers.

See answer to pete.

 

[Davisonp]

If the switch was connected across neutrals surely you'd have mains potential on one side of the switch when off -an open neutral ?

That is what I would expect, but the contact voltage tester says there is nothing, and that is what is confusing me.

 

[Davisonp]

I could have wired my megger MFT up to the earth of a socket and used that for a voltage identifier, but with a mum trying to keep three under 10 kids away from me while I investigate I did not want to go back to the van for extra equipment or have extra trailing wires around the house and I wanted to get sorted and safe as quickly as I could.

 

[sparksburnout]

Inducate WTF is inducate

That is what I would expect, but the contact voltage tester says there is nothing, and that is what is confusing me.

If all else fails, you could always chuck this non contact carp in the bin and do some good old dead testing?

 

[westward10]

This really is rudimentary fault finding, assuming there is a fault.

 

[Davisonp]

This really is rudimentary fault finding, assuming there is a fault.

I have found the fault, and am asking if my interpretation is correct.

 

[westward10]

So what was the fault, in a few sentences.

 

[Des 56]

I have found the fault, and am asking if my interpretation is correct.

Sorry Dave I don't want to come over as "holier than thou" but, Have you found this fault?

Reverse polarity is a fault,unless this is definitely proven one way or the other,this potential fault remains

 

[sparksburnout]

I have found the fault, and am asking if my interpretation is correct.

The question is, did you use the procedures you were taught during your training? I can't remember the bit about using a non-contact voltage tester? You should be doing basic dead tests to identify this type of well, basic, fault? It does rather sound a bit chaotic.

 

[buzzlightyear]

with a mum trying to keep three under 10 kids away

never work with dogs or children in house.

 

[PEG]

You cannot make an assessment of what voltages are present,using the method stated,regardless of the number and age of any kids running about.

Please do not take this the wrong way,but a customers arrangements can never,usurp the correct method of either proving or testing. It just creates a potential risk,and can slow down finding any fault.