Permanent live?

BBM77 · 15-08-2007 10:43am #1

I am putting in a new light in my bathroom. I need to find a permanent live wire in the attic. Does any one know how I could find a permanent live without having to cut any wires? Can this even be done?

Mr Magnolia · 15-08-2007 12:30pm

Why do you need a permanent live?

With the greatest respect Bally, it does sound like you should consult an electrician in regards to your requirements but, by all means come back and ask more questions I would like you to provide a little detail though

BBM77 · 15-08-2007 1:12pm

Mr Magnolia wrote:

Why do you need a permanent live?

With the greatest respect Bally, it does sound like you should consult an electrician in regards to your requirements but, by all means come back and ask more questions I would like you to provide a little detail though

I am putting in a shaver light over the bathroom sink. I need to find a permanent live so the light can be switched on independently and not only when the bathroom light is switched on. I am going to use a junction box so I don’t what to be cutting wires until I find the right one. All the wires look the same so I am wondering is their a way to know which is the permanent live as apposed to the wires that are only live when the light switch is in the on position. I am sorry I cannot be clearer, thanks for getting back.;)

Mr Magnolia · 15-08-2007 1:27pm

Thought it was for a shaver socket alright. You may have a permanent feed at your main bathroom light if the 'Three Plate Ceiling Rose'* method was used to wire your lighting circuits.

Three Plate Ceiling Rose method involves looping a live, neutral and earth around all the lights in the 'zone' and running a twin-brown to your light switch (live and switch wires). If you open the light fitting in the bathroom and discover 2 separate terminal/connector blocks with brown cables wired to them this would mean this wiring method has been employed and you have a permanent live/feed here.

There are other ways I could advise you to do this using fused-spur-outlets but you would need to be fairly competent to understand me and to carry out the work.

My advice to you is get an electrician in as no matter what way you choose to carry out the work a certain amount of it will be invasive.

*Not sure if this is the exact name of the system but the cabling system is the same regardless.

BBM77 · 15-08-2007 2:01pm

Thanks for that, I will check it out when I get home:)

Doolittle51 · 15-08-2007 2:07pm

There is a permanent live at the lightswitch for your bathroom. You could loop from there. Should be easy to fish a cable down the wall if they are normal partition walls. Then loop the neutral/earth from the light fitting.

Stoner · 17-08-2007 9:03am

Have to back up Mr Magnolia here, I'd advise that an electrician did this.

There should be a permanent live at the switch, the method of wiring Mr Magnolia mentioned is less common but keeps all the live wires at the light fitting and brings a feed and switch live to the light switch, if you are lucky there will be a permanent live at the fitting.
Most installations involve the permanent live wires (feeds) being looped at the light switches so the light fitting connection will only have a switched wire.

Anyway if it was me doing it this is what I would do, I'd only did this if the following instructions made perfect sense to me.

Assumptions
It is an upstairs bathroom, I have attic access and the attic is un-floored.

I'd get a phase tester and check if I had a permanent live at the switch,I'd do this by seeing which live cable lit up the phase tester regardless of the position of the light switch, the switch wires will flick the phase tester on and off with the light switch, the permanent will just stay on regardless of the position of the light switch until I turned off the MCB or fuse.

I would then turn off the power to this circuit by leaving the light on and turning off its MCB, when the light was out and the identified live wire was tested dead with the phase tester along with all other cables in the the back box, I would head for the attic.

I'd identify where the cables go down to the light switch and give them a light tug to see if they are loose.

I would then go back down to the switch and get a friend or son to help me.
I would get them to go into the attic and lightly tug each cable until I could see one that moves at the switch, if the cables were all very tight with no movement I'd leave it unless I was happy plastering up the walls afterward.

With the loose cable identified I would disconnect if from the switch and attach some 1.5.sq.mm PVC/PVC Brown cable to it via insulation tape, I'd leave the new cable on its roll for the time being.

The with it attached I'd shout up to my helper to lightly pull the identified loose cable up, I'd keep an eye on it at the switch and feed the cable into my helper until he/she had pulled the cable all the way up.

When my helper had pulled the new cable up into the attic and was holding the taped joint of the old and new cables I would cut the new cable on the roll at the switch.

In the attic I would attach another new cable via tape to the joint in the attic (I'd keep these joints as slim as possible and they would not be 3 cables thick anywhere)

then at the switch I'd pull down the cable that I had just cut off the roll,
In doing this I would be pulling the old feed cable and a new cable off the reel back down to the switch, when i had them down I would have the old and a new cable at the switch and the other end of the new cable would be on the roll in the attic waiting to be brought to it's location (the shaver light).

I'd connect the old feed and leave the new cable with its end taped up sitting in the back of the box unconnected and I'd replace the light switch.

I'd pop on the MCB and make sure the light worked.

I would not connect the new permanent live cable into the switch until I had the other end in the shaver light connected and during all connections I would have the power to the light switch off (even though the end of the new permanent live is taped up)

But that's me, If I felt that this sounded complicated to any degree I would not do it, I'd get an electrician an this has been our advice so far anyway.