I see that there is multicore flex rated at 6A for central heating applications. Is it permissible to use this for a light switch, after all, the load would be within the 6A limit, or must T&E be used for fixed applications? I ask because I have a single light switch that I would like to upgrade to a 2 gang, 2 way light switch but there is only one length of oval conduit buried in the plaster.
I don't think I can fit two runs of 3&E down the conduit and I am not ready to chase and re plaster the room just yet, so I wondered if I could drop some multicore down the conduit and terminate it in a junction box above (notwithstanding the debate whether a junction box under floor boards is accessible!) until such time as the walls can be chased and more conduit added.
Personally I would say not good workmanship, but I might do it in my own house ...
Another alternative is to shove 1 x 3+e for the existing switch down the oval, and use a ceiling pullcord switch as a temp measure for the second light.
Another option, IF you have enough oval conduit exposed above is to get one of those rare beasties, an oval-round adaptor, then work a make or female
20mm adaptor onto the end, glue the lot with the solvent weld stuff and put a proper conduit style or square junction box on the end. Providing you can get a 100% enclosed conduit[1] run between the light switch and the junction box, you are then OK to use "singles" down to the switch (single insulated single core wires - buy from TLC or another trade counter). Crimp or screw strip in the junction box to normal T+E.
[1] This is necessary for regs compliance.
Flex is allowed. However it could be wired up using a 3 core and earth and a
2 core and earth if both lights are on the same MCB. The standard way of wiring a 2 way light switch has one of the terminals at permanent live so you only need to pull one perm live down and link it behind the lightswitch between the two switches.
Thanks, that's good to know. I'm wondering whether to bite the bullet and chase the wall sooner rather than later and have it done properly from the start. If I chase the wall and then plaster over the new conduit, will the new plaster "blend in" with the surrounding plaster or will I always be able to see where I cut the chase? Will it be necessary to skim the whole wall or use lining paper to hide it?
Ideal is bootlace ferrules on the end - useful for all flex applications especially the very small sizes.
You used to be able to pick up a mixed-box of Tyco Amp bootlace/flat/ pin on ebay quite cheaply. Then it is the bootlace ferrule ratchet crimper which TLC do (normal reg-blue-yellow will not work).
3C+E is possible as stated.
No need to skim the whole wall or use lining paper, indeed you do not need to redecorate if you have spare paper :-)
1A - If you have plaster over browning (sand cement)...
- Make a slightly wider jagged slot in the plaster with a HD stanley blade than you need
- Then scrape out the browning as necessary
- If it appears "blown" PVA the sides of the browning to rebond to wall, done
1B - If you have just plaster...
- SDS-chisel or chase-tool can be done directly if plaster isn't blown
- If it is do as above
2 - Make a chase...
- Goggles, gloves
- a) Diamond disc, arbor, cordless drill on low speed & goggles
- b) Diamond chase tool or angle grinder
- c) SDS chase chisel
3 - Fit round conduit for this application...
- Twin 20mm round is ideal, 25mm is a bit excessive
- Use a 47mm backbox so enough space even for Grid etc
4 - Plaster to hold conduit in place (&/or use clips)
5 - Plaster flush, drawing the trowel UP the wall as it firms up
6 - When plaster just green, shave plaster flush by trowel
- Green means the plaster is not quite powdery but solid shavings
- Hold the trowel at an angle and plane the plaster flush
With a little bit of effort the new chase is quite invisible.
Aside - If you have spare wallpaper you can put that back (you cut thro new & old, peel off old, new will but invisibly). The exception is if you had lining underneath in which case things get more difficult re matching thickness etc. Paper discolours with age so it is then a matter of cleaning/blending if necessary.
Aside - If the switch is "central" to the house, it might be worth leaving enough space for outside light switch. Some people prefer PIR lights, others prefer manual on/off and a central location can be handy. Just something else to consider.
In addition to Wireless, 3C+E you can go "French" and use a remote relay but that needs to be accessible. They routinely use such for 2- way switching in place of the UK system, then probably make the parts obsolete... :-)
Sorry, I'm not quite following you. I need one 3&E for each gang in addition to bringing the live down. I know you usually drop a twin brown and earth down for live and switched live and for a 2 gang switch, yes I could share the live and use a 3rd 3&E for live, switched live 1, switched live 2, but I would still need the other two
3&Es to run to the terminals on the second switch so that would make three 3&Es, so I'm still needing three cables or am I missing something?
Both lights are on the same MCB but I thought you couldn't have two different circuits at one switch?
A 2 gang 2 way light switch only needs 5 phase conductors and an earth for the back box to make both switches work. All the clever bits are done in the
Sounds perfectly safe in pragmatic terms, as long as appropriate teminations & joints are used. I am not an electrician, just a householder on a budget.
Sorry, I hadn't realised you were including a junction box. You are quite right that if you use a junction box I can drop fewer wires. I understand now. Thanks.
You only need the five conductors even without the junction box. I would drop two three core and earths myself, it makes it easier for the electricians to understand what is happening.
Not sure how unless all the terminals were done at a light fitting. Space is often at a premium behind modern light fittings and could make things interesting.
That is what the OP wanted to do. He has not got enough space in the existing conduit and is not wanting at this moment in time to chop into the wall.
I have decided that I will chase another conduit now and do it properly from the start.
Earlier in this thread someone mentioned if two lights were on the same MCB. I thought that you weren't supposed to mix rings (or radials since we are talking lights) inside a switch. Is that just a good idea rather than a regulation?
That got me wondering when you would want two different radials to go to one switch. The only thing I could think is if you had indoor lights on one MCB and outdoor lights on another. Wouldn't it be better to put them on separate switches in separate boxes?
Drifting further off-topic, I then wondered if you could put the two switches into one dual box? The reason I have started to doubt this is that the dual boxes appear to have two earth terminals: one for each switch. Now in the unlikely event of a fault on A, the current would flow through earth A and earth B. Does this have any implications? I suppose it would also cause problems if you were going around testing earth loop impedance if you were unaware that another earth was there?
Anyway, enough daydreaming, I really must find that chisel ;) TIA
There is nothing wrong or unusual about the power behind a lightswitch coming from 2 different MCBs. This is most often seen in a hallway where a 2 gang light switch is used for the hall and landing. The landing light is usually on the upstairs lighting circuit and the hallway light on the downstairs circuit. It would look unsightly to have two switches.
Parallel earths do affect earth loop readings. They will not however impact upon the safety of an installation.
When I was trying to think when you might have two gangs of a switch connected to two different MCBs, I almost thought of the stairs and landing but then I realised that in the (few) houses I have lived in, the landing light has always been on the ground floor MCB. Perhaps that's why I thought you couldn't mix MCBs in a switch?
I suppose that if you mix MCBs in a switch there is the risk someone only isolates one MCB and gets electrocuted off the other, but then if the landing light is on the downstairs MCB, someone could isolate the upstairs lights to work on it and electrocute themselves, so there are disadvantages to either system. I guess the moral is check and double check the power is off first.
I just wondered whether it might mask a problem if the earth on A was broken, it might appear to be intact because of earth B, but if earth B was working then I suppose you could argue that it doesn't matter as long as there is a connection.
In a very, very extreme condition, I suppose someone could isolate A and be electrocuted of there was a fault on B but that would be very very rare and I am clutching at straws here. I suppose no system is perfect.
Grid (modular) wiring accessories often have multiple supplies exposed within them, eg radial-1 radial-2 radial-3. The larger MK Grid faceplates do include a warning "Isolate All Supplies" label which should be attached to the metal grid frame. Modular wiring accessories in particular need such a label because the metal grid frame once populated with switches will obscure the cables underneath from both vision and short-nosed voltage detectors.
Conventional wiring accessories often have multiple supplies passing through them, that is to say the cable merely passes through using the box to define a BS7671 zone. An example would be a power cable passing through a light switch backbox to a power socket located inline further down the wall. A more common instance where both power & light cables would share the same conduit is a surface run round conduit in a garage or shed.
All cables are assumed live until individually proven dead - and that includes L+N+E and any other cores. Even then where a "borrowed neutral" installation fault exists it is possible for a tested-dead wire to become live once disconnected. An example of the a "borrowed neutral" is where the alternate positions of a hall switch move the hall lights off the downstairs MCB to upstairs MCB and vice-versa (something usually found by the unwary when the two circuits are later split across 2 RCD or 2 RCBO).
If you did not wire it all, you assume the worst - Main Switch is there for a reason :-)
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.