different lighting wiring

[tbs1983]

Hi Guys, I'm from a mainly industrial background so looking for an experienced domestic sparky who can help out.

My mate asked me to change a couple of old pendants in his house for new ones.
Went there tonight to do them, in both pendants (different rooms) were 3 x double insulated single cores. One of which was connected to the line side of the rose, and the other 2 were connected to the neutral. (no earth present, not uncommon in older lighting circuits)
I thought it was strange but thought there may be a borrowed neutral case going on or something.
On disconnecting the old pendant I powered up and was surprised to see that I was getting 230v across the 2 cores connected to the neutral side.
Anyone come across this type of wiring method before? I can't fathom it out to be honest. I assume there are JB's above in the ceiling somewhere but why the need for this rogue 3rd neutral core that is seemingly live?

Any help will be greatly appreciated!

 

[tbs1983]

note - both were 1 way circuits.

switches were off when I was getting 230v across the 2 'neutral' cores

 

[Pete999]

Hi what colors are the singles I did a lot of house bashing when they used single cables, it may be in your case that you have a neutral in and a neutral out, and a single switch wire, thet did supply them with a cpc but not that many firms used them. If the cables are all black, the sparky may have used a black single as a switch wire, you may have measured 230 across a neutral and the switch wire, hope this helps.

 

[tbs1983]

Thanks for the quick reply, the neutrals were black/black, the live was black outer/red inner.
I was definitely getting 230v across the two black/blacks.

The mistake I failed to make was to open a switch to see what was in them.

 

[Pete999]

Not sure what to say, felt sure that was the problem, what have you got at the switch?

 

[overskilled]

Did you test across L->N? Wondering if polarity is reversed?

 

[tbs1983]

Makes total sense what your saying, in fact i'm starting to think it is wired in the way you described. in effect they just ran a single neutral from db - rose - rose - rose etc, then did the lives from db - switch - switch - switch etc, and then ran in a single switch wire from each switch to each rose.
Just wondering why I was picking up this voltage across the 2 disconnected neutrals ? perhaps my testers were playing up!

 

[overskilled]

Also is there any conduit hidden in the ceiling, did a house recently where it looked like no earth on the lighting circuit, untila bit of poking and prodding revealed a conduit box that had been buried in plaster over the years

 

[Pete999]

Thats right N to all the lights, L to all the switches and a SW from light to switch, I did 1000s of them, what meter were you using?

 

[Pete999]

Also is there any conduit hidden in the ceiling, did a house recently where it looked like no earth on the lighting circuit, untila bit of poking and prodding revealed a conduit box that had been buried in plaster over the years

Doubt if they used conduit with double insulated singles, but stranger things have happened

 

[tbs1983]

Just a small martindale voltage/continuity tester. didn't have full test kit with me.
I didn't lift any floorboards or anything to find conduit or the like.
Literally just swapped 2 old roses for 2 new ones.
Pretty sure it must be wired as you described. Makes total sense now. Think my tester must have been picking up some false readings.

Thanks for the help, learnt something new again today (1970's wiring methods!)

 

[Pete999]

No problems us old furts have their uses from time to time

 

[showerman]

Hi , have you put your tester in SERIES with the 2 neutrals and are picking up the voltage
being sent from one of the other lights trying to complete the circuit ? you need to make sure all other switches are off and /or lamps removed , this should explain the reading you were getting .

 

[MDJ]

Hi Guys, I'm from a mainly industrial background so looking for an experienced domestic sparky who can help out.

My mate asked me to change a couple of old pendants in his house for new ones.
Went there tonight to do them, in both pendants (different rooms) were 3 x double insulated single cores. One of which was connected to the line side of the rose, and the other 2 were connected to the neutral. (no earth present, not uncommon in older lighting circuits)
I thought it was strange but thought there may be a borrowed neutral case going on or something.
On disconnecting the old pendant I powered up and was surprised to see that I was getting 230v across the 2 cores connected to the neutral side.
Anyone come across this type of wiring method before? I can't fathom it out to be honest. I assume there are JB's above in the ceiling somewhere but why the need for this rogue 3rd neutral core that is seemingly live?

Any help will be greatly appreciated!

Come on man think about it, neutral in and neutral out, single switch wire from switch, lamps in and you are making the circuit with the tester.

 

[benji]

don,t suppose light in adj. rooms could have been switched on could they

 

[tbs1983]

Thank you showerman! The lightbulb has literally just switched on in my head !!!! Makes perfect sense now!!!

Why didn't I think of that before !!!!

Thanks guys for all the help, the case is now closed!

 

[Pete999]

Can't see the lives from the neutrals lol

 

[KAS1]

If you split the 2 blacks them "power up" and measure across the 2 blacks If there is another light switched on somewhere on the circuit you will of course pick up 230v across the 2 blacks lol

 

[MDJ]

Can't see the wood for the trees you mean Pete

 

[Pete999]

Yep something like that.

 

[R G]

If it was working before and you have i/d off the live return wire to the pendant , and the other cores were in the neutral bar , then no problem , the reason you are getting 230v between the neutral is because the its the return through the other lamps on the circuit .

 

[tbs1983]

Cheers Ray, understand it now. Thanks for the help (and the usual sarcastic comments from the trolls).
Done a bit of new housebashing but Not worked on 2 many older installations. Once the wiring method was established by the very helpful Pete, the answer to the voltage problem made sense.

Thanks again

 

[MDJ]

(and the usual sarcastic comments from the trolls).

Nothing Sarcastic at all, you were encouraged to think about what happened, you understand now and got your answer, don't be so Touchy :troll: