Replacing More Faceplates - Switches Have No Earth Available

[cwcw]

I am changing a few more faceplates from cheap plastic ones to metal ones. I have done this a few times now but seem to come across new problems each time! This time, in 2 of the switches there is no earth, despite metal back boxes.

The switches are a 2 way hall/landing and a 1 way landing light. Both have a single red wire coming into the top and going to the Common terminal, and both have a three-core cable coming up from below with one black into L1 and one black with red sleeve going into L2, with the 3rd core being snipped. I am assuming this snipped cable is what would be the earth - is there a way to test this or is it a case of putting the plastic plates back or getting in an electrician? Why would anyone snip the earth core anyway when it can just as easily and more safely be scewed to the backbox?

Additionally, the landing light did appear to have a single earth coming up from below, separate to the 3 core cable and screwed to the back box, but when I unscrewed this and pulled it away to put into the switch it came clean off in my hand! I looked with a torch through the hole but could not find any evidence it ever came from anywhere. The upstairs was rewired before we bought it so I am thinking it was there for show - is this likely or could it break off that easily in my hand? It seems unusual for a single earth cable on its own, not coming from the conduit.

 

[NewOrder]

The earth core might have been added at an extra date to make the existing circuit comply with the regulations. Don't even think about putting on metal face plates until you are more than 100% certain the earth is there and working.

I would just get a spark in to check your electrics over. I am just a DIYer but that is what I would do in these circumstances. Guessing costs lives.

 

[cwcw]

The earth core might have been added at an extra date to make the existing circuit comply with the regulations. Don't even think about putting on metal face plates until you are more than 100% certain the earth is there and working.

I would just get a spark in to check your electrics over. I am just a DIYer but that is what I would do in these circumstances. Guessing costs lives.

Maybe, but I don't see how it would just pull off in my hand. I've cut several bits of extra earth cable for these plates before, to link them to the back plates, and it takes some doing with a sharp stanley knife. It seems unlikely it would just snap off in my hand like that - it just looks like it was there for show.

I've already put the plastic ones back but now I am worried about the metal screws that hold these in - I've gone from blissful ignorance to paranoia. I'm even starting to doubt whether faceplates I've already changed before are properly earthed if the wiring is so dodgy - is there a way I can test this without having to pay for an electrician to look at every single one?

 

[ericmark]

In the 1980's I was working in the Falklands and on a friends farm he got a belt from the washing machine so I went to look at the earths. I wish I had never started each time I connected an earth I found the next one disconnected and finally found there was a break in the earths some where in the loft space where I had no access.

Since that time I have found this is common once you find one disconnected you find many more and only real answer is either a rewire or all class II fittings.

As to the why with lights that's easy before 1960 we never bothered with earths on lights.

Testing well the real method would be using a low ohm ohmmeter like I did on the Falklands although I know many use an earth loop impedance meter and work live.

I have a few times in the past tried to bring in earth wires but one of the problems I have found is where an earth is borrowed then it is all too easy in the future for that circuit from which the earth was borrowed to be removed and in so doing removing the earths again.

My mothers house is also without earths on the lights and just the other day I was talking about the problem with my son and we felt with the disruption involved with a re-wire class II was the way to go and once emergency fittings are fitted then to RCD protect the lights.

 

[aesmith]

The switches are a 2 way hall/landing and a 1 way landing light. Both have a single red wire coming into the top and going to the Common terminal, and both have a three-core cable coming up from below with one black into L1 and one black with red sleeve going into L2, with the 3rd core being snipped.I am assuming this snipped cable is what would be the earth - is there a way to test this ...

Is the third snipped core insulated, or just bare copper wire inside the sheath? You can test continuity with other earths elsewhere if you have a meter.

 

[cwcw]

The switches are a 2 way hall/landing and a 1 way landing light. Both have a single red wire coming into the top and going to the Common terminal, and both have a three-core cable coming up from below with one black into L1 and one black with red sleeve going into L2, with the 3rd core being snipped.I am assuming this snipped cable is what would be the earth - is there a way to test this ...

Is the third snipped core insulated, or just bare copper wire inside the sheath? You can test continuity with other earths elsewhere if you have a meter.

The snipped core is bare. It's a single wire in the sheath, quite thick, whereas the live and neutral either side of it are insulated and have multiple thinner wires. How can I test if it's an earth? Would a multimeter and some reading up help?

 

[aesmith]

The snipped core is bare. It's a single wire in the sheath, quite thick, whereas the live and neutral either side of it are insulated and have multiple thinner wires. How can I test if it's an earth? Would a multimeter and some reading up help?

Assuming a half decent electrical installation, you'd expect that to be the earth, although I wouldn't expect it to have been just cut short like that. It should really have been sleeved and then terminated. If you have a multi meter, you could measure resistance from the cut end to another earthed point in the system (check there's no voltage on it first though).

 

[Adam_151]

I've already put the plastic ones back but now I am worried about the metal screws that hold these in

Assuming the metallic screws are in contact with the box (many of the 16mm boxes around when lighting circuits were unearthed had nylon blocks for the screws to go into)

Then if you do find switch points without an earth then you can get nylon plate screws, just make sure you run the re-threader through first even if the hole seems fine, the nylon screws are much weaker than the metallic ones

 

[cwcw]

This picture shows what the cabling is like:

http://www.heluxgroup.co.uk/page/upload/modproduct_4bfb985d5f501_b1.jpg

The differences being that the colours are the old ones, and the middle earth core is snipped back to the grey sheath. I'm now pretty sure it is twin and earth cable that has been snipped back and I will buy a multimeter to verify this. If it is, and assuming there is sufficient slack or a safe way to extend it (?) I can connect the earth to the new faceplates. If there is no earth continuity I will be getting an electrician in to make it safe.

 

[ericmark]

I used a 13A Plug with an earth lead only connected to the earth pin of the plug as a reference point when testing for earth in a yet to be powered up house.

It is not perfect as you don't know the earth loop impedance of the socket you are using but it does the job good enough for what you need.

 

[PrenticeBoyofDerry]

As you will now have realised that the issue will not just be at this particular switch, but will likely to be common throughout your lighting circuit, so you are going to come across similar earth/CPC(Circuit Protective Conductor) problems at switches and fittings and very likely junction boxes/joints within ceiling/floor voids, these will all need to be addressed to get continuity throughout this circuit. Then you would also need to check that there is actually and earth/CPC at the board for this circuit.
It is not unusual to find single cores at the board and no earth/CPC for lighting circuits, even though there is evidence of an earth/CPC at other parts of the circuit.

Even though it is not unusual to come across lighting circuits that have no CPCs in installation dating back to the 60s, you also come across ones that used the metallic conduit as a path to earth.

A multi meter or low ohms reading continuity meter will be a helpful tool to confirm the continuity of the earth/CPC.
This test is performed with the circuit isolated and is generally done using one of two methods.
1) r1+r2, these are the Line/live(r1) cables and earth/CPC(r2). These conductors are connected together at the fuse board, the meter is nulled out and test made at lighting, switching and junction points, testing across live/line and earth/CPC.

2) Wander lead, this would require running a long lead to lighting/switching points from the earth/CPC at the board. The lead will need to be nulled out from the reading taken and the test is done between lead and earth/CPC at the accessories.

http://www.tlc-direct.co.uk/Book/8.4.1.htm
http://www.youtube.com/watch?v=fQJVNsi4X24

 

[ericmark]

PrenticeBoyofDerry is correct you should test back to the board as you know the valve of the long lead so you can get an accurate reading, however not sure if you really need such an accurate reading? although the ohms setting of a multi-meter will show there is an earth, at 7.8Ω which is the maximum allowed loop impedance without RCD protection permitted, your multi-meter will be rather inaccurate, it requires a special low ohm meter, which uses at least 200ma to do the test, to get accurate readings so using a know good earth is good enough.

One would hope that your 13A sockets do have good earths so using a 13A plug with just a earth wire connected to it long enough to reach to centre of the room should be a good enough reference point when only using a multi-meter.

Personally I would swap all fitting to class II and dump all metal fittings as PrenticeBoyofDerry says likely you will end up doing a part re-wire before you get it all earthed correctly but multi-meters are cheap enough so yes no harm in testing and finding out how many earths are missing.

Do remember with plastic switches the 3.5mm screws are still earthed to back box which makes testing easy but also means to get class II status you need the little plastic bungs on top of the screws. As a quick fix I have used silicon sealant on the screw heads to make sure no one can touch the screws holding on the switch plate.

 

[PrenticeBoyofDerry]

An alternative to metallic screws with insulated caps, would be to use Nylon machine screws.

 

[cwcw]

I'm thinking I will just get an electrician in to do an inspection. If any earthing needs adding then they will just have to do it with hopefully minimal disruption. I do have an installation cert dated 10 years ago to say ground floor earthing was done and upstairs fully rewired though, so hopefully it's all there but just not connected up properly.

 

[PrenticeBoyofDerry]

I do have an installation cert dated 10 years ago to say ground floor earthing was done and upstairs fully rewired though, so hopefully it's all there but just not connected up properly.

If it was not done/connected correctly, then the certificate has false information on it as it seems obvious that this is not true, depending on the interpretation of earthing, don't confuse earthing conductor and main earth bonding, with that of the earth/correct terminology CPC (circuit protective conductor) of the lighting circuit.
But it could well be that someone has made alteration since that cert was issued!
Does your document display r2 or r1+r2 values for the lighting circuit within the schedules of tests and are there any remarks regarding this on the document.