Is it safe to use a metal light switch faceplate on a non-RCD protected circuit?

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Hello,

I've decided to do my first ever bit of electrical work - Starting simple with replacing a plastic wall mounted light switch with a sunken metal one.

I noticed on the consumer unit that half of it is RCD protected and the other half isn't, the lights being on the side that isn't. It made me think, would this be safe using a metal faceplate? I am of course going to attach the earth to the metal faceplate and run another earth wire from there to the backbox.

Cheers

Edit - Also while i'm here, does anyone know if there's any reason it would be a bad idea to use the screws off the old faceplate and cut them down in length a bit so they fit the new backbox?
 
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I noticed on the consumer unit that half of it is RCD protected and the other half isn't, the lights being on the side that isn't. It made me think, would this be safe using a metal faceplate? I am of course going to attach the earth to the metal faceplate and run another earth wire from there to the backbox.
Yes, perfectly normal. Must be earthed.

Edit - Also while i'm here, does anyone know if there's any reason it would be a bad idea to use the screws off the old faceplate and cut them down in length a bit so they fit the new backbox?
Of course not, but new ones don't cost much - then you'll have some long ones when you need them.
 
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Yes, perfectly normal. Must be earthed.


Of course not, but new ones don't cost much - then you'll have some long ones when you need them.

Thank you for the reply. The thing is i can't seem to find any the right length, even on Amazon. I was worried that if i cut them, the end could be rough and when i screw it down, cut into a cable. I guess i could dremmel any sharp bits.

Do you happen to know how i test that the earth is actually doing it's job? I did read something about using a multimeter, one on the live (with electric on) the other on the earth wire on the continuity setting on the MM but i swear that doesn't sound right and can't seem to find an answer online. I'm terrified of something going wrong and have two little ones that love to climb on chairs and turn the lights on and off. There is a thin earth cable coming out the wall outside, messily wrapped around a drain pipe and going into the soil. It does not look legit lol
 
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Edit - Also while i'm here, does anyone know if there's any reason it would be a bad idea to use the screws off the old faceplate and cut them down in length a bit so they fit the new backbox?

They can be very difficult to use, if you just cut them with a saw, unless you fit a (steel nut is best) nut first to tidy up the cut end of thread. Best thing I have found to cut them, is a cheap crimper, which had a series of threads for cutting different brass screws. Unscrewing it after chopping, cleaned up the thread.
 
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Thank you for the reply. The thing is i can't seem to find any the right length, even on Amazon. I was worried that if i cut them, the end could be rough and when i screw it down, cut into a cable. I guess i could dremmel any sharp bits.
Yes, remove any sharp bits by whatever means.

Do you happen to know how i test that the earth is actually doing it's job? I did read something about using a multimeter, one on the live (with electric on) the other on the earth wire on the continuity setting on the MM but i swear that doesn't sound right and can't seem to find an answer online.
You are not supposed to work with live wires but sometimes it is inevitable.

You must determine that the earth wire in your switch is connected to the Main Earthing Terminal at the supply.
You would need a multimeter and a long wire.

There are other ways which might be good enough but that is the only way to be sure.

I'm terrified of something going wrong and have two little ones that love to climb on chairs and turn the lights on and off. There is a thin earth cable coming out the wall outside, messily wrapped around a drain pipe and going into the soil. It does not look legit lol
I doubt it is anything to do with that - or shouldn't be.
 
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They can be very difficult to use, if you just cut them with a saw, unless you fit a (steel nut is best) nut first to tidy up the cut end of thread. Best thing I have found to cut them, is a cheap crimper, which had a series of threads for cutting different brass screws. Unscrewing it after chopping, cleaned up the thread.

Thank you, i will try this.

Yes, remove any sharp bits by whatever means.


You are not supposed to work with live wires but sometimes it is inevitable.

You must determine that the earth wire in your switch is connected to the Main Earthing Terminal at the supply.
You would need a multimeter and a long wire.

There are other ways which might be good enough but that is the only way to be sure.


I doubt it is anything to do with that - or shouldn't be.

I've got a multimeter and bought 25m of 1.5mm2 earthing cable today, would that be suitable?

Sorry to be a pain but do you know of any guides on exactly what to do? Scares the poop out of me working on live wires so i want to make sure i have every step clear in my head.

Why is the length of the screw so different than what was there before?

Currently there is a plastic surface mounted light switch, i am putting in a flush metal one with a 16mm back box imbedded into the wall. The screws for the surface mounted one are 2.5cm where i imagine i need about 16mm. I find it so odd they are hard to find in shops - screwfix minimum was 2.5cm but what about all the people using 16mm back boxes...
 
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There are two ways to test the earth, one uses a low ohm meter and is done dead, the meter must use at least 200 mA for the test, but you need to know the earth loop impedance at the consumer unit to work it out.

The other uses a loop impedance meter, and is done live.

The impedance (called resistance with DC) has to be low enough to work the overload within a set time, a B type MCB will trip on the magnetic part of the trip in the time allowed if the current exceeds 5 times rated current plus 5% so with a 6 amp MCB that is 230/30x95% = 7.28Ω the problem is these meters are expensive, and any other method will not give you the reading to filling in the test certificate.

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It is unlikely many DIY people bother with the Zs reading or the paperwork, they just trust to the lord, in real terms if doing DIY no option.
 
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There seems to be a lot going on here, so trying to keep things simple...

I noticed on the consumer unit that half of it is RCD protected and the other half isn't, the lights being on the side that isn't. It made me think, would this be safe using a metal faceplate?

Are you sure only half of the consumer unit is RCD protected, can you post a picture of it and we may be able to confirm! :)

You currently have a surface mounted switch and back box.

i am putting in a flush metal one with a 16mm back box imbedded into the wall. The screws for the surface mounted one are 2.5cm where i imagine i need about 16mm.

Personally, I would go for a 25mm back box (if you are happy to drill a bit further into the wall). It will give you more space to play with to get the wires to fold back into the box neatly.
Where you knock out a hole for the wire to enter the back box, you will need to use a rubber grommet to protect the cable.
Switches are usually supplied with new screws - you dont want nasty chewed up screws spoiling the look of your new switch! :)
There won't be any need to cut screws to size.

I've got a multimeter and bought 25m of 1.5mm2 earthing cable today, would that be suitable?

Sorry to be a pain but do you know of any guides on exactly what to do? Scares the poop out of me working on live wires so i want to make sure i have every step clear in my head.

You don't need to work on any live wires to check the earth continuity. Just use the continuity setting on the multimeter, connect one probe to the earth in your rewired switch, and the other to ideally the main earth terminal of the supply (probably next to the CU). If you can't achieve that, try the earth of a nearby socket - hopefully the multimeter will beep! A resistance measurement can also be taken.

Lastly, if it really worries you - stick with a plastic switch on the metal back box. It won't give you sleepless nights and you would have achieved something that will give you confidence.
...or consider having an installation inspection by a qualified electrician at some point soon! :)
 
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A rethreading tool (M3.5 x 0.6) for the switch/socket boxes is invaluable. Toolstation do them, as do Screwfix. There are many suppliers on E-Bay as well. Prices seem to be around £7.50-£8. The rethreading tool has got me out of trouble when I have cross threaded a particularly awkward socket box screw!
 
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Is this a "flat-plate" light switch? if so then I STRONGLY recommend a deeper backbox. Even for a regular switch 16mm can be pretty tight.
 
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Edit - Also while i'm here, does anyone know if there's any reason it would be a bad idea to use the screws off the old faceplate and cut them down in length a bit so they fit the new backbox?

I recently had to replace some surface mount plastic switches for a mate. He purchased the "screwless" plates from Screwfix- the types where the face plate clips in the main body


The screws provided were far too short. I couldn't use the existing screws though because they need to be counter sunk and not dome head. I ended up having to use socket extension studs, and then cut the supplied screws. I used my (cheapish) side snips to cut them. I did however find that running the screws counter clockwise before screwing them in clockwise prevented cross threading.
 
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Sorry to be a pain but do you know of any guides on exactly what to do? Scares the poop out of me working on live wires so i want to make sure i have every step clear in my head.

Advice if you must work live is - Wear insulating footwear, make sure arms and legs are covered, plus work with only one hand - hopefully dry and not sweaty. Keep the other in your pocket. Idea is to prevent current flowing through your body, especially from one arm, to the other - because your heart is in the middle. A shock across your one exposed hand, is less of an issue, it just hurts.
 
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Have I missed something? The OP hasn't said that they need to work with live wires- they simply mentioned that the stuff that they are working on is not RCD protected. Provided that they flick the correct MCB, and check the circuit, then, erm.. they won't be working on a live circuit. I am not an electrician but it might be helpful if one of you guys assure them.
 
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I find this all very strange, lots of folk use metal faced light switches, they are everywhere these days and perfectly safe unless seriously interfered, which the average child would be incapable of unless he were to set about using a hammer with all of his might. It's true that "only half" of modern consumer units are protected with an RCD - the power and cooker circuits which can carry a heavy load due to the thickness of the cables used but all circuits (including those for lighting) are never the less protected by MCBs these days which switch off instantly if there is a problem and are far safer than relying on just an earth wire. Only twice in the past 20 years have I seen old style units protected by fuse wire although I guess there may still be a few about. I was taught at tech college that the speed of current cut by an MCB was such that it would not be able to kill a two year old. Think about it, if metal light switches were at all dodgy, they would not sell very many would they?
 

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