wobbly voltage

[buddha]

a bit of twin and earth controlled by a one way switch that i was gonna wire a new light to showed 240v with the switch on ,and 200v with the switch off.

the other gang in the switch controlled some existing lights,and when the light was turned off,the wire in L1 showed 240v,but when switched on with the light working,showed no voltage! in this gang i think the neutrals are being switched.

not sure whats going on in the first gang of switch with the voltage going to 240v with switch on and 200v with switch off.

any of you more clever sparkies got any possible explanations?

 

[NozSpark]

The first one sounds like an induced voltage,, as you don't have a load on the cable the voltage on it can float (there is very little if any current available though).. DMMs don't show as a load in this instance, only moving coil meters will

On to problem 2... What are you measuring the voltage on L1 with respect to? You do know that we are not allowed to only switch the neutral??

 

[buddha]

thanks for the reply,yeah i know switching neutrals is dodgy,its old wiring,theres probaly a birdsnest of a junction box somewhere.I stepped back from it as I dont want to add to already dodgy wiring.

On the piece of t&e i was gonna wire new light to,between black and earth i got 240v ,between red and earth i got no voltage,do you reckon the black is live and the red neutral? and could i use this as a live and neutral feed to another a new switch i could install,running my new switch line and neutral from here.

thanks for taking an interest.

---------- Post Auto-Merged at 17:29 ---------- Previous post was made at 17:25 ----------

noz,what are DMM'S? i measured between earth on an adjacent switch,(as the earth in problem switch didnt seem to go anywhere) and L1

 

[NozSpark]

DMMs are Digital Multi Meters mate,,, like I said they don't appear as a load on a circuit

If it is truly a switched neutral the voltage will show as 230v ish when off and will drop to as near as zero when it's on

and if it is a switched neutral,, 1 it will need sorting and 2 you cannot use it as L&N as the L is fed through a lamp

 

[ProDave]

Are you sure you are not just looking at a red and black at the light switch, where red is live in, and black is switched live out, and there is no neutral at the light switch?

To be absolutely certain, take a wander lead back to a KNOWN good neutral point somewhere to measure from.

 

[monkey5]

Are you sure you are not just looking at a red and black at the light switch, where red is live in, and black is switched live out, and there is no neutral at the light switch?To be absolutely certain, take a wander lead back to a KNOWN good neutral point somewhere to measure from.

my thoughts too, maybe the sw live and perm live are "wrong" way round, or if its pretty old maybe its wired with one of them really orgainsed square junction boxes with all light feeds and sw lives go back to them.

wayne

 

[sellers]

Are you sure you are not just looking at a red and black at the light switch, where red is live in, and black is switched live out, and there is no neutral at the light switch?To be absolutely certain, take a wander lead back to a KNOWN good neutral point somewhere to measure from.

Good advice, if theres any confusion on which conductor is what in these circumstances I always go back to the board with a long lead to confirm.

 

[buddha]

not sure if they are the wrong way round in the switch,no voltage switched on but light works,voltage present switched off,would it matter if i swapped the two around?

---------- Post Auto-Merged at 11:16 ---------- Previous post was made at 11:14 ----------

DMMs are Digital Multi Meters mate,,, like I said they don't appear as a load on a circuitIf it is truly a switched neutral the voltage will show as 230v ish when off and will drop to as near as zero when it's on

and if it is a switched neutral,, 1 it will need sorting and 2 you cannot use it as L&N as the L is fed through a lamp

thanks noz,dmm came to me last night,the penny dropped when i was half asleep ha ha,thanks for the advice.

 

[ProDave]

not sure if they are the wrong way round in the switch,no voltage switched on but light works,voltage present switched off,would it matter if i swapped the two around?

That does sound like you have just two wires in the switch, a red and a black.

With the switch off, the red will be live, and the black will be connected, via the resistance of the lamp to neutral, so with a meter will read 240V across the switch.

And of course with the switch turned on, both will now be live, but a meter connected across the switch will of course read zero.

Are there JUST these two wires in the switch, or any others?

Have you done a proper test yet with a long lead back to a known neutral to give a proper reference point?

 

[buddha]

thanks pro dave,i didnt do the long lead test.

It was a 2gang switch,a red going to one common then linked to the other common,a black in each L1.

I put one probe on an earth from another nearby switch,and then the other probe on L1,240v off/ov on.

I did the same for the other gang and didnt get a voltage with switch on OR off,yet this switch effected the bit of t&e it was supposedly supllying,and changed the voltage there from 240v to 200v on/off.

I will give the long lead a go,thanks for taking the time to help.