Switched Neutral?

[Tempiz]

Hi,

Just bought new ceiling Pendant to replace a rather sorry looking one in my fathers bedroom. After isolating the lighting circuit at the CU, I opened the existing rose ready for removal only to find a peculiar wiring arrangement.

The existing rose is a normal loop type, but the 2 cables fitted don't seem right to me even though the light works. I know that in the past the electrician who did work at my parents house had done some pretty shoddy lookin wiring, and on one occassion never came back to complete the job leaving taped up live cables sticking out the bathroom wall. The builder who subbed him in appologised but never got it completed. I digress however!

The light fitting is fitted to the 'flex' outputs as normal, there is a 'live' connected to the 3 part neutral bar. its coressponding neutral is connected to the 2nd output of the 'live' bar (not the loop) and a cable with its live conducter cut off has its neutral connected in the same 'live' output as the other cable. I looked in the switch and found just a usual looking set up as if it were switched live.

By chance I have the floor board up in the room above so was able to partly trace the cables. The cable with the cut off live seems to go back to a junction box with 4 cables in. 2 of the cables are joined live for live, neutral for neutral etc, but the other 2 are joined neutral to neutral and have the lives cut off.

Any ideas what is going on here? Was there a 'once upon a time' when switched neutral was the norm. Wiring is about 20 years or so. I could probably rewire the rose taking a loop from the bathroom next to the bedroom as the floorboard that is up covers both rooms. Am just unsure if the single neutral is supplying the junction box or vice versa.

As always, many thanx in advance for your thoughts and advice.

 

[Taylortwocities]

There has never, ever been a time when a switched neutral was the norm.

Just because the wire is coloured black (blue nowadays) doesn't necessarily make it a neutral. Its a black wire, it could be a switched live (and probably is). If it is a switched live then it should have a red (brown) sleeve to indicate it is/can become live.

Its impossible to say what is going on unless you can furnish photos of
the ceiling rose
the switch
the junction box

 

[Tempiz]

Thanx for the reply, but to reaffirm:

two twin and earth cables going into ceiling rose, one has live and neutral connected albeit on the wrong connectors, i.e live is on neutral side and neutral connected to live next to flex connector. Second twin and earth has ONE conductor only which is neutral (black) and has been connected with the other neutral on the live bar next to the flex live output. The Live (red) conductor of the 2nd T&E has been cut off. No tape/sleeving to indicate if switched live on black conductors.

switch has usual red and black conductors present, indicating should be switched live.

Nearby junction box has 4 x T&E, 2 are connected pole to pole, other 2 have red conductors cut off and the black joined together seperately to the other 2 cables.

Cant upload photos at present as using parents PC with no software for my camera or phone.

 

[sparkwright]

i'm not quite clear where the two single black wires are connected to within the junction box. do they go in with the two blacks, or with one black or one red? couldn't quite follow that part of your post.

also, at the switch is it one normal twin and earth cable; or is it two twin and earths with some cores cut out? or something else? where does that other black at the junction box go to?

is all of the property like this or just that area?

 

[Tempiz]

Hi sparkright, thanx for the reply.

In the ceiling rose there are the usual 3 seperated connector bars, Neutral, loop, live. The neutral is taken up with the Blue of the lamp holder and a RED of T&E. The BLACK of the same T&E is connected to the live bar next to the brown flex of the lamp holder. Also within this live connector is a BLACK from a seperate T&E, but the RED is cut off.

Found a junction box under the floor above which has 4 T&E. 2 of them are connected pole to pole, with a third T&E RED on the 'live' connector. The Black from this 3rd T&E is connected to a seperate connector. A fourth T&E Black is also connected, but this has the RED conductor cut off.

Within the switch is one T&E normal in appearance to any switched live setup. Only this light in the house as far as I have found is connected in this manner. The others are a mixture of switched live with connections either in the rose or the switch where the neutral of two cables are connected in chock block while the 2 lives are in the switch.

 

[sparkwright]

so the centre loop terminal at the rose is empty?

 

[sparkwright]

when the light is on is it usual brightness? not really dim or anything?

 

[Tempiz]

Hi, Yes, loop is empty.

Light works fine as it has done for the last 20 years or so, no dimming etc. Am just wondering if all the switching and is in the junction box under the floor above and all the installer did was send the return to the rose rather than using the loop. Seems an odd way to do things. My biggest concern is the reversal of the 'Live & Neutral' in the rose. didn't want to correct it, not knowing how they are connected elsewhere. Just looks a bit rough. Have put it all back together with a new pendant set and is still working ok. Gonna be one of them little niggles knowing that it's there!!

 

[sparkyspike]

I'm wondering whether the light is wired up normally - it's just that the LIVE and NEUTRAL connections at the rose are the wrong way round. This won't alter the function of the light and the neutrals won't be switched. But if it's an ES fitting, it must be rewired the right way round.

Best thing to do is to use a multimeter to prove which cables are live, switched live and neutral and label them accordingly. Otherwise you are just guessing. It's possible you do have a switched neutral - I have found them in the past - so it may be worth checking to make sure and to avoid future problems like the one you are having now.

 

[ericmark]

Reading your posts this is what I think you have.

Ceiling Rose

• ericmark
• 31 Aug 2009
• 3

And from that it would seem some one has borrowed a neutral from the lights.

However removing the wire could cause more danger than leaving it where it is as if removed you may have some thing which does not work but is still live.

As to regulations the term "borrowed neutral" is used when the live and neutral do not come from same isolator and if the junction box you refer to is still part of lighting circuit it may be OK.

However until we can be certain then we could very easy give wrong advice so maybe you can alter the picture and show exactly what you have.

 

[ColJack]

Hi, Yes, loop is empty.

sounds like someone has just put the light back the wrong way..
the block with 2 connections is the switched live, the block with 3 connections that is not the loop is the neutral block..

 

[Tempiz]

This is a diagram of the rose and the junction box under the floor above. Am not able to trace all the cables in the JB, but am fairly sure the switch cable is in there and the cable with the red cut off. May also be one of the T&E with both conductors connected.


View media item 14122
Ericmark, had considered it being a borrowed neutral, but only 2 cables coming in which would need to be supply and switched something! Was leaning towards it possibly being switched neutral as a mate of mine had come across a few when rewiring older properties is the past.

ColJack, I had considered that, but given the rest of the wiring in the JB I cannot say for certain so have left as is.[/img]

 

[sparkwright]

have drawn out several wiring diagrams based on the information given. don't know how to post them, but surprised your light even works! is there another junction box hidden somewhere? is there another switch back to back with this one in another room which may contain some sort of joint? is a light in another room somehow directly involved in this wiring set-up?

 

[Tempiz]

Not sure about another JB as only 2 floorboards up, but the 2 nearest switches less than a metre away are both wired in a loop config as far as I can tell. No joins made in con block etc and only one cable in the switch. Gonna be one of them mysteries I guess. Am just amazed as to why one of the condutors has been cut off!