Changing from / to a dimmer light switch

Andrew · Post by **Andrew** » Mon Nov 20, 2006 7:14 am

Hi, I have a dimmer switch in one room and a normal switch in another. What I want to do is swap them. Is this okay to do? Does a circuit have to be "special" or the bulb be specific to accept a dimmer switch, and also visa versa?

If this is okay to do, can I guess the wiring is the same for both?

Thanks.

Andrew · Post by **Andrew** » Mon Nov 20, 2006 11:02 am

Actually, I need to amend this post, having just seen the Ultimate Handyman webpage that tells you in detail what to do!

However, what if my wiring doesn't have an earth wire? I can't check as I'm at work, but I'm 95% sure that my light switches (and possibly the plug sockets) only have two wires.

Is this a problem? I've read that simply connecting an earth wire from a switch to a socket (i.e. not connected to the mains) is pointless. True? Should I just ignore the earth part?

By the way, all my face plates are plastic, although the boxes in the wall are obviously metal.

Any help would be appreciated.

tim'll fix it · Post by **tim'll fix it** » Mon Nov 20, 2006 12:10 pm

I would be worried if your sockets dont have earths.

However it is common for lighting to have the earths clipped off (although very bad practise)

if you really have no earth you should consider a rewire

Andrew · Post by **Andrew** » Mon Nov 20, 2006 12:34 pm

I'm not exactly Mr electrical DIY, and my memory isn't so good, so I could well be wrong. I'll have to check tonight.

At least, I hope I'm wrong. I'm not having a re-wire.

I'll let you know later...

Post by **ultimatehandyman** » Mon Nov 20, 2006 1:00 pm

You can not use dimmers on Flourescent Lamps or most low energy Lamps!

Years ago they never used to use the earth wire on lighting circuits as it was common then to fit a plastic ceiling rose.

The lights really should be earthed as under fault conditions it is still possible to touch the screws holding the faceplate to the backbox.

Sometimes the earth wire will still be there, but has been snipped off at the same length of the PVC coating.

If the sockets also have no earth then it is time to start to give this some serious attention, and you could be looking at a full rewire. Having no earths on a lighting circuit with plastic face plates carries much less of a risk than sockets without earths- this is downright dangerous!

When you get home check the sockets and if there is no earth then it is time for a full re-wire!

Andrew · Post by **Andrew** » Mon Nov 20, 2006 5:29 pm

Right, I have just checked one light switch (the one I intend to swap) and one double plug socket. The good news is there are earth wires in both. The bad news is I must be stupid, as I remember wiring them in now! However, I just want to be clear, so...

Light switch:
1) At the moment, it's a two way switch, although it's only being used as a one way. I take it there is nothing to worry about if i revert back to one way when I fit the dimmer?
2) Like I said, there is an earth (the bit you split the sheath with). It's not got a coverslip on it, and it simply goes from the circuit to the metal box and then stops there. It doesn't go to the face plate, but then there's not a place for it to go on the faceplate (it is plastic after all; do they only have a place to earth the face plate if it is made of metal?).
3) Can I assume that all my lighting will have this type of wiring (do you call it core and earth?)?

Plug Socket:
1) I simply copied what was there previously, which is: two earth wires joing together to go into one earth terminal. Is this sufficient or does something else need to be done?
2) Things you might want to know: it is a plastic faceplate, and there are two earth terminals, one not being used.

Many thanks once again.

Andrew
<soon>

Post by **ultimatehandyman** » Mon Nov 20, 2006 6:26 pm

That is good news

Light switch:
1) At the moment, it's a two way switch, although it's only being used as a one way. I take it there is nothing to worry about if i revert back to one way when I fit the dimmer?

That will be fine.

2) Like I said, there is an earth (the bit you split the sheath with). It's not got a coverslip on it, and it simply goes from the circuit to the metal box and then stops there. It doesn't go to the face plate, but then there's not a place for it to go on the faceplate (it is plastic after all; do they only have a place to earth the face plate if it is made of metal?).

This is quite normal, but there should be green and yellow earth sleeving over the earth wire really. The earth wire often terminates into the backbox. If you were to fit a switch with a earthing terminal you would terminate the earth wire to the earthing terminal on the faceplate and the backbox as well, this is acheived by using a small lenght of earth wire that goes from the face plate to the backbox, as well as connecting the earth wire of the circuit to one or the other.

3) Can I assume that all my lighting will have this type of wiring (do you call it core and earth?)?

Well you should never assume anything but it is more than likely that the rest of the wiring is like this, but you can not be sure without checking. The cable is called core and earth. Twin core and earth is the most common, three core and earth is used in two and three way lighting circuits.

Plug Socket:
1) I simply copied what was there previously, which is: two earth wires joing together to go into one earth terminal. Is this sufficient or does something else need to be done?

This is also very common, but now it is more common to split the earth wires and place one in each terminal, these should also be sleeved with green and yellow sleeving. If you have metal backboxes then you should also cut a small length of earth wire and fasten it between the socket earth terminal and the earth terminal of the back box, so that you have an additional earth. This should be done regardless of whether the socket is plastic or metal.

You can see how to wire the short piece of wire from a switch or socket back to the backbox on this page ( known as supplementary earthing)- http://www.ultimatehandyman.co.uk/repla ... switch.htm

sparkydude · Post by **sparkydude** » Mon Nov 20, 2006 6:27 pm

The bare earth wire in your light switch should be sleeved in green/yellow sleeving,as should any bare earths in your eelctrical system. Your socket is wired fine, but as a safety measure it is normal practice to run an earth lead (piece of bare earth core sleeved) between the terminal on the backbox and the faceplate. This is recommended as there have been a lot of cases of decorators removing sockets to wallpaper or paint behind and then sticking a scraper or suchlike onto the live terminals and blowing themselves up, the earth lead will help with a good earth path and help the protective device(fuse or MCB ) to operate more efficiently. Swappng your switch and dimmer is an easy operation as you said there is a guide on here to help you out. Any problems get back to me here

Nick

Andrew · Post by **Andrew** » Mon Nov 20, 2006 8:11 pm

Thanks sparkydude and UHM. It's nice to know the setup isn't immediately dangerous :!: Just to wrap this up, some final questions:

1) I take it that the circuit earth cable(s) are meant to touch the supplimentary earth cable (both in sockets and switches), so it in effect becomes an extension. If that's correct, then would it be incorrect if I kept my plug socket setup (both circuit earths terminating into one terminal) and then supplimentary bonded from the metal box to the unused earth terminal on the faceplate? If I was to do that, the supplimentary earth would never "physically" touch the two ciruit earths.

2) Is there any advantage to using the two earth terminals or could I rightly keep with the two earth wires going into just one of the terminals? THis probably ties in with the answer to question 1.

3) Final question - if I went to buy some earth cable for supplimentary earthing, what type would I need to buy? Is this cable all the same, in other words?

Many thanks.

sparkydude · Post by **sparkydude** » Mon Nov 20, 2006 8:28 pm

Nothing wrong with using the other earth terminal for your box earth, it will be joined by the meatl strip inside the socket anyways. If you wish to install these earth links then you can either buy some stranded 1.5 conduit cable for the purpose or just get some offcuts of 2.5twin and earth cable, pull out the earth,sleeve up with green/yellow and use that for the purpose.

any more questions feel free to ask

Nick

Post by **ultimatehandyman** » Mon Nov 20, 2006 8:41 pm

1) I take it that the circuit earth cable(s) are meant to touch the supplimentary earth cable (both in sockets and switches), so it in effect becomes an extension. If that's correct, then would it be incorrect if I kept my plug socket setup (both circuit earths terminating into one terminal) and then supplimentary bonded from the metal box to the unused earth terminal on the faceplate? If I was to do that, the supplimentary earth would never "physically" touch the two ciruit earths.

It is not uncommon to see all three earth wires pushed into one earthing terminal, but for some reason unknown to me it now says in the on site guide that the earth wire needs to be wired so that one wire goes in each of the two earthing terminals. As you are not fitting it from new I don't see why you cannot put all three earth wires into one terminal, but it would be best if you could put one in each and then a supplementary wire in one of them leading to the backbox.

2) Is there any advantage to using the two earth terminals or could I rightly keep with the two earth wires going into just one of the terminals? THis probably ties in with the answer to question 1.

I am not sure, but I am sure there is a good reason for it.

3) Final question - if I went to buy some earth cable for supplimentary earthing, what type would I need to buy? Is this cable all the same, in other words?
Normally you would use the central core from the wire that you are using to wire the circuit, called the CPC. Normally a piece of this would be stripped and used and then covered with green and yellow earth sleeving.

If you have some twin core and earth cable knocking around you can use the cpc from this and get some green and yellow sleeving. You must use the correct wire though, so if it is for the lights use the cpc from either 1mm or 1.5mm twin and earth. If it is the sockets use the cpc from 2.5mm twin and earth. You can use the 2.5mm twin and earth cpc for the switches as well as the sockets if you like but you can't use the cpc from the 1mm or 1.5mm twein and earth for the sockets as it would be too thin.

You can buy a couple of meters of 2.5mm green and yellow sleeved wire and supplementery bond all your sockets and light switches at once-

http://www.tlc-direct.co.uk/Products/CA2dot5SGY.html

2.5 mm may be a bit over the top, but I once did a full house with 4mm as it was what I had available at that time. You can use thicker wire than recommended but never thinner wire.

Let us know how you get on

p.s. Make sure you do it with the electric turned off

Andrew · Post by **Andrew** » Sun Nov 26, 2006 10:26 am

UHM - you say you can't use a dimmer switch on flurescent or most low energy lamps. Can you use them with spot lights / recessed lighting? I have four recessed into the ceiling in one room and want to put them in other rooms where the dimmer switches will be? Does it depend on the type? I've got the fitting instructions and it doesn't say they can't be used with dimmers. The ones I currently have are 50watt mains halogen.

Ta.

sparkydude · Post by **sparkydude** » Sun Nov 26, 2006 10:28 am

THEY SHOULD WORK FINE ANDREW, JUSTY MAKE SURE THE DIMMER IS OVER RATED TO THE LOAD YOUR PUTTING ON IT, FOR YOUR 4 LIGHTS YOU NEED AT LEAST A 250w DIMMER.

NICK

OOPs didnt realise caps lock was on oh well not writing it all again

Andrew · Post by **Andrew** » Fri Feb 09, 2007 8:41 pm

Here's a stupid question...

...If I install supplimentary earthing to my socket boxes, this doesn't mean that when the power is on, the box would be "live", does it? I don't make a habit of unscrewing the face plate, sticking my fingers inside and touching the metal box when the power is on, but I'm just intrigued... :sign3:

Post by **ultimatehandyman** » Fri Feb 09, 2007 9:03 pm

No, the metal back box would only be live under fault conditions and because it is earthed/bonded you would either feel a small shock under fault conditions or the fuse/mcb would trip/blow.

You shouldn't really remove the sockets with the electric switched on, it is bad practice.

If you were to get a shock it could be your last!