Cable for switch drops.
Discussion
I have a situation involving a triple lightswitch (3 switches in one unit, so do we call it a 3 gang?) and I want to run three new cables to it.
All of these will eventually control relatively low lower lights, but I first want to reinstate a ceiling light which will have three 40 watt bulbs. I've not yet decided what the other two switches will do, but one might control an external 400 watt PIR halogen light, and the third switch might be used to control another outside light of fairly small wattage.
Anyhow, the thing is that going up from the switch unit is a fairly slim conduit buried in the plaster, so that gives limited space for cables. So, what I'd like to do is run three cables up the conduit and into the loft and pick those up later with junction boxes/connectors of some sort to serve the various lights.
I have some cable which was bought for connecting thermostats to valve actuators in our underfloor heating system, and this cable is type 2192Y, which is twin (live and neutral) i.e. 2 x 0.75 mm2, and if it is technically acceptable I'd like to use this cable for the switch drops. Normally we would use 1.0 or 1.5 mm2 cable for lighting, but in this case I'm hoping that 0.75 mm2 will be OK.
My feeling is that it should be satisfactory in terms of current carrying capacity, as the cable runs will be short, and they will not be wrapped up in insulation or anything of that sort, but what do you think?
Your advice and guidance will be much appreciated.
All of these will eventually control relatively low lower lights, but I first want to reinstate a ceiling light which will have three 40 watt bulbs. I've not yet decided what the other two switches will do, but one might control an external 400 watt PIR halogen light, and the third switch might be used to control another outside light of fairly small wattage.
Anyhow, the thing is that going up from the switch unit is a fairly slim conduit buried in the plaster, so that gives limited space for cables. So, what I'd like to do is run three cables up the conduit and into the loft and pick those up later with junction boxes/connectors of some sort to serve the various lights.
I have some cable which was bought for connecting thermostats to valve actuators in our underfloor heating system, and this cable is type 2192Y, which is twin (live and neutral) i.e. 2 x 0.75 mm2, and if it is technically acceptable I'd like to use this cable for the switch drops. Normally we would use 1.0 or 1.5 mm2 cable for lighting, but in this case I'm hoping that 0.75 mm2 will be OK.
My feeling is that it should be satisfactory in terms of current carrying capacity, as the cable runs will be short, and they will not be wrapped up in insulation or anything of that sort, but what do you think?
Your advice and guidance will be much appreciated.
curlyks2 said:
Flexible 0.75mm2 cable appears to be rated to 6A ( source). As you say, 1.0mm2 or 1.5mm2 T&E would be more normal. If you use your twin cable, how are you planning to earth the switch(es)?
Hi, and many thanks for your reply.I was planning to connect a single earth wire to the terminal in the metal back box, with a short connection onto the back of the switch unit as well, though all the exposed parts of the switch unit are plastic. The end of the earth wire within the back box would have green and yellow sleeving. The other end of the earth wire would then be connected to the earth connections in the junction boxes in the loft.
I'm hoping that would be safe and satisfactory, but perhaps you would be kind enough to let me know if you think it would be inadequate.
speedyman said:
Run a triple (3 core + earth) and a two core 1.0mm2. Loop one live feed to each switch common and use the other wires as switch lines. Joint box in loft above.
Thanks for the suggestion, and I'm not suggesting your scheme is wrong, but I don't understand it. It'll need a bit of thinking about at this end. Electrical stuff is not exactly my specialist subject.In any case I'm not sure that I have sufficient space within the existing (quite small) conduit to accommodate what you suggest, and I was rather hoping to use the 2 x 0.75 mm2 cable that I already have available.
The scheme is easier to understand if you draw it, but essentially you only need one "in" wire, and then you have three "out" wires going to each light from the switch (switched live).
Think of it like the water in your house - you have one mains feed, which is branched off with separate taps - you wouldn't have separate mains feeds for each room (bathroom, kitchen, etc)
Think of it like the water in your house - you have one mains feed, which is branched off with separate taps - you wouldn't have separate mains feeds for each room (bathroom, kitchen, etc)
p1esk said:
I thank curly, speedyman and Pheo for their helpful advice, and from their suggestions I've no doubt I shall be able to achieve what I want and have a safe system.
On the other hand I find Alucidation's comments quite unhelpful.
PH: great for getting helpful advice.....but I have to say I'm a little with the one you found unhelpfulOn the other hand I find Alucidation's comments quite unhelpful.
I'm all for fitting a new ceiling lamp or replacing a switch myself, but once I'm not sure on things, I have to firmly agree I would call in someone qualified.....sorry to hear you find that advice unhelpful...
I think the point is you have to have a long hard look at what you want to do, and how confident you can be that its a robust solution which meets BS7671, and any other applicable regs.
IF after doing your research you are not confident that you can do so, then you should not consider yourself a competent person, and should get a competent person in to do so.
IF however after doing your research you can be confident you can produce a standard of work which will exceed regulatory requirements, and subsequently be safe, then you could consider yourself a competent person.
So for example, I think its broadly OK to ask for help to understand and learn the safe circuit design parameters, provided you can then actually execute. If you remain confused/unsure, then it would be sensible to seek the help of a qualified professional. Your definition should include things like crimping wires correctly, how much insulation to strip, how to ensure continuity of earthing etc.
I think all Alucidnation is trying to make sure is that you don't blow yourself up, or create a hazard. Electricity can and does kill, start fires etc, so needs to be taken seriously.
IF after doing your research you are not confident that you can do so, then you should not consider yourself a competent person, and should get a competent person in to do so.
IF however after doing your research you can be confident you can produce a standard of work which will exceed regulatory requirements, and subsequently be safe, then you could consider yourself a competent person.
So for example, I think its broadly OK to ask for help to understand and learn the safe circuit design parameters, provided you can then actually execute. If you remain confused/unsure, then it would be sensible to seek the help of a qualified professional. Your definition should include things like crimping wires correctly, how much insulation to strip, how to ensure continuity of earthing etc.
I think all Alucidnation is trying to make sure is that you don't blow yourself up, or create a hazard. Electricity can and does kill, start fires etc, so needs to be taken seriously.
Pheo said:
I think all Alucidnation is trying to make sure is that you don't blow yourself up, or create a hazard. Electricity can and does kill, start fires etc, so needs to be taken seriously.
Surely electricity is not as dangerous as it used to be?What, with all these RCD's, RCBO's etc that are available nowadays, if you did cock up with the wiring, all it's going to do is trip out?
By the way, I converted an old Methodist chapel about 35 years ago and did all the wiring myself. If I wasn't sure of anything I'd go to the library and look it up. (No internet in those days)
Alucidnation said:
Jesus.
You yourself have said you basically don't really know what you are doing so rather than risking it, why not get a registered electrician in to do it for you?
You are already contravening the regulations with your 'idea'.
This^^^^^^^^^You yourself have said you basically don't really know what you are doing so rather than risking it, why not get a registered electrician in to do it for you?
You are already contravening the regulations with your 'idea'.
Then again its Bank holiday weekend so everyone is allowed to do anything..........Wait for the BANG!!!!
Electrical stuff is not exactly my specialist subject......
well then dont feckin touch it ! simples.
When will folks get it that you dont mess with electricity ? And asking for advice on a forum that you can not be sure if you will get an answer back that meets with the regulations etc.
the wire you were discussing was it rated for mains connection or extra low voltage use ? How are you planning on undertaking the connections to your final loads ?
The switch your talking of using a three gang switch. if your only doing simple on off for the light then you only need a switched live for each light. The switch needing four wires and an earth. Id use 1mm. run two lengths of twin and earth down. live goes to one terminal of all three switches. The three other terminals are wired back to the terminal box using one core on one cable and two on the others. red sleeves used to designate that they are the switch wires.
It is easy enough to do but even the slightest doubt then get someone in to do it for you.... its much safer in the long run and you wont be left with a burnt out house.... or even worse.
well then dont feckin touch it ! simples.
When will folks get it that you dont mess with electricity ? And asking for advice on a forum that you can not be sure if you will get an answer back that meets with the regulations etc.
the wire you were discussing was it rated for mains connection or extra low voltage use ? How are you planning on undertaking the connections to your final loads ?
The switch your talking of using a three gang switch. if your only doing simple on off for the light then you only need a switched live for each light. The switch needing four wires and an earth. Id use 1mm. run two lengths of twin and earth down. live goes to one terminal of all three switches. The three other terminals are wired back to the terminal box using one core on one cable and two on the others. red sleeves used to designate that they are the switch wires.
It is easy enough to do but even the slightest doubt then get someone in to do it for you.... its much safer in the long run and you wont be left with a burnt out house.... or even worse.
You could use 1.5mm2 single core cable, which is designed to be used in conduit.
https://www.tlc-direct.co.uk/Main_Index/Cable_Inde...
If you don't need such long lengths, go to your local wholesalers and ask for some end of reel bits.
https://www.tlc-direct.co.uk/Main_Index/Cable_Inde...
If you don't need such long lengths, go to your local wholesalers and ask for some end of reel bits.
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