2 way light switch


Postby pga1 » Mon Apr 07, 2008 2:16 pm

Can someone please help me - I want to change a single light switch to a double so that it operates two different lights in the same room. I called an electrician and he told me that becuase the switch cable had a green gunge in it the whole of the upstairs lighting ring would need replacing. Can you please tell me what causes the green gunge (something to do with the copper?) and am I I being given the correct information about having the whole ring replaced?
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Postby ericmark » Mon Apr 07, 2008 7:42 pm

There are two oxides of copper cupric and cuprous one blue/black the other green something to do with how the link with oxygen. As to cables if they become damp they can oxide and just like rust with steel it will degrade its ability to carry current. PVC coating on cables as well as insulating them tends also to stop any erosion traveling up the cables. However the old rubber cables tended to have problems here and it did seem to travel up the rubber making it unsafe to do anything but replace them.
We stopped using rubber around the 1950's not sure exact date but around same time as we went metric. And for lights also older houses had no earths which now is not acceptable. So how old is the wiring? If before 1960 then most likely it does require a rewire. After 1960 then it could still need it but I would be wanting to look at a little more than one switch to say all the lights need rewire. If he has seen something like missing earths then I would have expected him to have pointed this out. So how old is it? Also if you follow the regulations all houses should be checked every ten years or less. It is your safety not only for getting of shocks but from fire. If the cables are old then I would want them all checked not just lights.
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Postby pga1 » Tue Apr 08, 2008 2:36 pm

The cable is earthed and in white pvc. Not sure how old it is but at least 15 years. Its still flexible and all the other cables look OK.
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Postby ericmark » Tue Apr 08, 2008 4:14 pm

I would get a second opinion. There is something wrong to get green gunge but I would not think that warrants a re-wire but white cable also makes me wonder this is one for Sparx if he's around. He knows more than me on this sort of stuff. White is normally low smoke cable but I wonder if colour used for something else in the past? I would get second opinion anyway.
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Postby sparx » Tue Apr 08, 2008 8:26 pm

Hi Guys,
There are several different issues here,
so first to the 'green-gundge'. There have been 2 or 3 articles on it in trade press, it is to do with plasticiser migration within the PVC, not harmful to the cable, not good for accessories connected as it can get in the works eventually, also not too good for the skin when working on connections. Not apparently affecting cables integrity.
White PVC used to have no significance and was normally used for surface clipped cables for looks. Now new white reserved for low smoke/fume cable as Eric suggests but not in this case due to age.
Now to the main point, just fitting a 2 gang switch won't allow you to control 2 independant lights unless wiring is done with live & Neutral fed first to switch, not often done 15 years ago, so if only one 2 core and earth at switch then some rewiring will be required anyway.
Think that covers it for now,
regards SPARX
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