Strange stray voltage

[polarity]

Any ideas on this one welcome...

Putting in the lighting circuit for this new kitchen. Pull a brand new wire from a lighting circuit MCB in the CU - have removed other circuit on same MCB to keep it simple.

Connectors are push fit Wagos in a Wagobox.

Have 2 existing (one way) wall switches and the loop cables are accessible wher they come out of the wall so using those.

Live comes from CU MCB to Wago, splits out into the two existing wall switches then come back in and connect to their respective load cables, the N's of which are connected to the N from the CU. Earths all connected back to CU (though no E in existing loop cables). All standard stuff... I assume.

So I rig up a temporary light to one cable and terminate the other with a choc block for testing. Power on.

First switch on = light on, switch off = light off.

Other switch on = 230v on cable, switch off = 48V ! (L-N & L-E)

So thinking there might be a leak through the switch, I pull off the switch plate and disconnect the wire - still 48V!!, disconnect wire to other switch, still 48V. Turn off everything else in the CU, still 48V. Remove the temporary light same problem there, though slightly less voltage.

Opened Wagobox and double checked everything and separated all the blocks - still 48v

MCB off= 0V

There is almost no current behind it (0.019ma) but it is an odd phenomena as as far as I can see it is coming off a disconnected wire!

Am I going insane? or is this a symptom of an average Multi Meter?

P.

 

[binky]

If new cable is running alogside other live cables then this may just be an induced voltage, otherwise I would be looking for a borrowed neutral off another circuit.

I would also Insulation Resistance check cable in case voltage is early signs of cable damage from over zealous cable pulling

 

[Apache]

is the cable run alongside another for a distance? This is just induced voltage as far as I can see

 

[polarity]

If new cable is running alogside other live cables then this may just be an induced voltage, otherwise I would be looking for a borrowed neutral off another circuit.I would also Insulation Resistance check cable in case voltage is early signs of cable damage from over zealous cable pulling

I though of the induced voltage, but as mentioned, it is still there even with all other circuits off at CU!

The only bit of cable that is not brand new is the 2m in the wall to the switches. so that is a possible suspect, dont have an insulation tester so will bypass with a new cable.

The N is connected at the CU.

 

[mikep]

Got to be inductance !!

 

[polarity]

Got to be inductance !!

Can that happen with nothing else live? I reduced it so this is the only energised circuit. I am measuring the 48v at the load end which is about 4m to the switch - where it is physically disconnected!

We are out in the sticks, no high wires anywhere and its not like CERN is round the corner! :|

Following Binky's suggestion I will bypass the loop wires buried in the wall tommorow, - an insulation breakdown there could account for it. ray

If not it must be sunspots ....

 

[polarity]

This is getting annoying! Got to sort it as I assume it would show up as an anomaly on final testing?

I have bypassed the wall cable and I am still getting the same result. removed the other circuit, same result. See pic...

Duff cable? High frequency interference? UFOs? headbang

 

[matt.leung]

is it possible that there is voltage in the earth cable, and that there is cross polarity somewhere in the circuit...

 

[ianmacd]

Have you checked this at the MCB?

 

[SPARKY TIM]

Have you checked voltage neutral to earth, could be cross polarity or lost neutral.

 

[polarity]

Have you checked this at the MCB?

With the MCB off there is no voltage, with it on there is 240.

I get the same 48v-55v with L-N and L-E, 0v N-E, if there was V in the E or N where is it going back to - the L is disconnected at the switch...

Going to put my tinfoil hat on...

 

[m4tty]

what program did you use to do that drawing mate, if you dont mind me asking

cheers

 

[polarity]

what program did you use to do that drawing mate, if you dont mind me askingcheers

Rhino, http://www.rhino3d.com/

Right, I think it must be the shiny new cable, I tested between the L feed from the MCB and the other L end of the load cable and I get 207V (test point on pic), same result if I go via the closed loop...

 

[polarity]

WTF is going on here?

Following in from ianmacd's suggestion to test at MCB see attached pic....

All circuits off, except the test one through a 6a MCB, that (new 2.5mm) cable to represent a loop is about 2m long and terminates in the block as you can see.

Conductive choc blocs? I have only ever seen this when dealing with very high voltage or very high frequency.

 

[Lurch]

Have you tried using a decent meter to test this?

 

[polarity]

Have you tried using a decent meter to test this?

I was so tempted to put "no coments about the cheap a** meter please" on the end of my post !

In fact in my original post I asked if it was possibly a symptom of an average meter. Anyway it does the job - at least it seems too as it has never invented voltage before.

 

[Lurch]

I was so tempted to put "no coments about the cheap a** meter please" on the end of my post ! In fact in my original post I asked if it was possibly a symptom of an average meter. Anyway it does the job - at least it seems too as it has never invented voltage before.

Electronic meters, cheap ones more so, tend to fluctuate wildly on what they show when they are presented with no load and a little EMF or similar. Sometimes putting a dummy load across the test circuit will stable them up.

 

[polarity]

Electronic meters, cheap ones more so, tend to fluctuate wildly on what they show when they are presented with no load and a little EMF or similar. Sometimes putting a dummy load across the test circuit will stable them up.

Ok, it has repeatedly given the same readings on the phantom voltage, but worth a try, what would you suggest as a dummy load?

 

[Lurch]

Ok, it has repeatedly given the same readings on the phantom voltage, but worth a try, what would you suggest as a dummy load?

Something that would present a reasonable (couple of k) load to the circuit to kill the stray voltage, a lamp may do it.

 

[binky]

Failing cheap test gear try circuit on different MCB, or possibly check for continuity through MCB (dead of course) - you haven't filled them up with dust have you????