Electrical Question

Cross polarity problem.

Hi all. I have a problem with the lighting in my house. Basically, there is a light switch at either end of the hallway and its only possible to turn the lights off from the same switch I use to turn the light on. ie. if I come into the house and use the switch there to turn on the
lights, I can only turn them off from that switch. I've been told its called cross polarity and even if the lights are switched off, they are still technically live. Its only occured recently after we had some boarding and skimming done on the ceiling. I would be grateful for any suggestions/remedies.
Thanks for the info everyone - have checked the switches and are all connected OK. Will post a job on here and get it looked at.

9 Answers

Best Answer

Suggested remedy. at the back of your switches will be 3 terminals in a triangle shape. the top is the 'common' and usually labled thus. the bottom 2 are l1 and l2.
Only attemp this if you are confident in your basic wiring skills.
Switch off all power. take the swithches off and look at the wires (take a photo if unsure).
one switch will have 1 wire in the common and 2 in l1 and 2 in l2. the othe switch should have 1 wire in each terminal common, l1 and l2.
a common fault here is the switch has been taken off and not put back right.(maybe during plastering??)
You must make sure that the 'common' in each switch is the same wire as the other switch. This should sort your problem...let me know if it does.

Another way which is practically the same. look for the switch with 2 cables (one will have 2 wires and an earth the other will have 3 wires and an earth) make sure the cable with 3 wires (one into each terminal) is wired into the same terminals in the other switch as they are in the swith you are looking at. ie. common to common, l1 to l1, l2 to l2.

Answered 9th Sep 2011


Member since 1 Sep 2011

I must first advice you to get a qualified electrician to attend site & investigate the problem.
its highly unlikely to be a cross polarity problem, but at a guess the workman or woman, may have damaged a cables that is used for the 2way switching when thy installed your new ceiling,

Answered 9th Sep 2011

Home Power Distribution Ltd

Member since 6 Feb 2010

on a 2 way switch you will have cable connection points marked
C. L1. L2. on one of the switches there should be one cable with
colours brown black and grey. or red blue and yellow,( depending how
old the cables are ). assuming it's the former,( switch of the power) put the brown wire in L1, the black wire in L2, and the grey wire in C. then go to
the other switch and there should be two cables, One with colours
brown and blue, and the other with colours brown, black, and grey.
put both browns in L1, the black and blue in L2, and the grey in C.
if this does'nt work email me back with more info.
Kind Regards
Phil Tatler

Answered 9th Sep 2011

Phil.Tatler Electrical&Security

Member since 6 May 2011

This sounds like the two way switches are connected wrong. There are two ways of wiring two way lighting, the conventional method and the conversion method. In order to help we need to know which wiring method is in place?

Answered 10th Sep 2011

DCM Electrical

Member since 23 Aug 2011

Hi sounds like your plaster have removed the switch or light and not fitted it back on correctly,easy fix for a qualified electrician


Answered 9th Sep 2011

I Parker electricals

Member since 3 Mar 2010

The two way switching has an incorrect connection or a cable has come out of a terminal. this would usually be at one of the switches if wired conventionally. When the ceiling was worked on did you also decorate the walls ie loosen the switches if so a cable may have dropped out of its terminal or even snapped off at the terminal, this would be the first place to check.
Unfortunately 2 way switching is not easy to describe in a few words on here. But it would be an easy job for a qualified electrician and would probably not cost a fortune to fix put it up on my builder as a job and save on your legs running back and forth

Answered 9th Sep 2011


Member since 9 Oct 2008

Hi Ado

Very hard to pinpoint your problem but if I understand it right it sounds like you have a problem with your stappers that go between the switches. If I were testing that is where I would start to see if one of the strappers has been broken ( possibly been screwed through ? ). The only surprising thing is that you said that only the roof was boarded, it is possible that it has been screwed through the roof but it would have been more likely to have been screwed through the wall. By getting an electrician in to test it should quickly resolve it, after that it is just a matter of locating the break.

Either way it does need testing thoroughly by an electrician. Hope this info helps.


NJM Electrical

Answered 9th Sep 2011

NJM Electrical

Member since 7 Mar 2009

is it just me or are you missing the obvious. If it was working fine before the ceiling was reboarded then I have to assume someone took down the light fitting to do this then put it back up incorrectly. Therfore the remedy would be to refit the fitting correctly.

In the past some older electricians used to wire up two way lighting from the rose to each switch so by this meathod of wiring it is possible to wire it up incorrectly from the ceiling rose and with the information you supplied i.e it was fine before the ceiling was done it has either been wired up incorrectly or the cables are damaged.

Answered 10th Sep 2011

kevin cassidy building contractors

Member since 16 Dec 2010

I asume that you are talking about two way lighting? When you had the skimming done, did they remove the switches? If so, it sounds as if a wire has come adrift. there should be 3 wires to one switch ( common, L1 & L2) and 5 wires to the other. As long as the same colour wire from the 3 core cable is in the common at each end and one wire from each of the 3 core and the 2 core are joined in L1 & L2, all should be OK
There would always be a live cable in a switch, even when it is turned off, as you are only putting a break in the circuit, so isolate at the fuseboard

Answered 10th Sep 2011

Evergreen Electrical Ltd

Member since 27 Jul 2009

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