Metal Faceplates - Lightswitch Wiring

[dk1uk]

Hi - please can someone advise on a couple of issues?

I am replacing my plastic lightswitches with metal ones. The instructions are clear - the faceplate must be earthed to the metal backbox.

I have two issues:

1. Some of my backboxes are plastic - so what can I earth the faceplate to?

2. Where the backbox is plastic, whoever installed the plastic faceplate has clipped the earth cable - is this right?

Many thanks in advance for you help.

 

[RF Lighting]

1. Some of my backboxes are plastic - so what can I earth the faceplate to?

There should still be an earth wire at the switch position.

2. Where the backbox is plastic, whoever installed the plastic faceplate has clipped the earth cable - is this right?

No it is not right.

You must NOT fit metallic switches if you can not reliably earth them.

 

[Adam_151]

I am replacing my plastic lightswitches with metal ones. The instructions are clear - the faceplate must be earthed to the metal backbox.

Its badly worded. The switch plate must be earthed. This can come from the metal box if it is earthed already, by installing a small link.

1. Some of my backboxes are plastic - so what can I earth the faceplate to?

Take the earth core of the cable from the holding terminal in the box and connect to the switch plate instead

2. Where the backbox is plastic, whoever installed the plastic faceplate has clipped the earth cable - is this right?

Thats wrong, you need your earth conductor to connect to your new switch plate. The installer who was there has demonstrated very bad practice and made your task 10x harder!. You are going to have to gain enough on the cable to be able to make a joint onto what remains of the earth!. In addition you are going to have to verify that the conductor is actutally connected to earth and whoever saw fit to just snip them off at this end didn't see fit to do it at the other end too!.

Do you own a multimeter?

 

[dk1uk]

Thanks for the replies. There's enough cable remaining back there for me to clip back live/neutral to gain enough earth, so that's a relief.

However, a very good point on whether it's been snipped at the other end...and my knowledge starts to fade. How can I check - where would I look?

I don't own a multimeter but I could buy one.

Thanks again.

 

[Adam_151]

You'd do a simple continuity test between the earth you wanted to test and the main earth terminal in the property (or something which you know is earthed to it - such as the main bond on you incomming water service)

You'd also need a long coil of wire as a 'wander lead'

If you dont have a multimeter then a you could get an old fashioned door bell, battery and a long lead wire it up with two leads (one long, one short) where you'd have the bell push, put it near your point with a known good earth and connect the short lead to earth. Take your long lead to your earth you want to prove and touch it to the previously snipped earth and listen for the bell ringing

 

[dk1uk]

Thanks again.

So I have been out to buy a multimeter.

Can I check that the following steps are correct to test the earth in the suspect light switch?

1. Isolate power.
2. Open a socket or lightswitch which I'm confident has an earth cable that is properly earthed.
3. Connect my wander lead to the earth terminal on the back-box of trusted socket/switch.
4. Open my suspect lightswitch.
5. Turn power back on.
6. Using my multimeter, touch one probe on the wander lead and the other on the earth cable in the suspect lightswitch.
7. If there's continuity, my multimeter will beep. If there's no continuity, then I should assume the earth in my suspect lightswitch is not connected?

Many thanks

 

[Adam_151]

Thats basically it. You might want to consider attaching yous wander lead to the bond on your water stop tap to avoid having to open up another point. (just strip it back quite a bit and wrap it around the screw on top). Or you could wire it into a the earth terminal of a spare plug top (ensure you don't have a brain fart and connect it to L or N tho!). Or you could just back of one of the screws on a socket front, wrap the end of the stripped wander lead around it, and tighten it back up (same with a consumer unit cover screw - if you have a metal con/unit)

 

[EFLImpudence]

1. Isolate power

Yes.

2. Open a socket or lightswitch which I'm confident has an earth cable that is properly earthed.

How will you be confident. You should use the Earthing Terminal in/near the consumer unit.

3. Connect my wander lead to the earth terminal on the back-box of trusted socket/switch.

As 2.

4. Open my suspect lightswitch.

Yes.

5. Turn power back on.

NO, NO, NO. Leave it OFF.

6. Using my multimeter, touch one probe on the wander lead and the other on the earth cable in the suspect lightswitch.

Yes.

7. If there's continuity, my multimeter will beep. If there's no continuity, then I should assume the earth in my suspect lightswitch is not connected?

Correct.

 

[Adam_151]

Missed his No.5, ELFI

 

[dk1uk]

OK, thank you, especially on the point about leaving the power off!

Question though - how do I identify the earthing terminal in/near the consumer unit? Sorry - not really ever done anything with the consumer unit except isolating the power.

One other question - so far, I have replaced a few switches with metal ones, connecting the available earth to the earth terminal on the metal back-box. Then running a new bit of insulated cable from the earth terminal on the back-box to the earth terminal on the switch...I've done this wrong haven't I? I should have connected the available earth to the switch, then run a new bit of insulated cable back to the back-box terminal. But...does it matter, or should I re-do them?

Many thanks again.

 

[EFLImpudence]

Question though - how do I identify the earthing terminal in/near the consumer unit?

You may have a bare metal block near the consumer unit with green and yellow wires connected to it or a G&Y wire connected directly to the incoming supply cable. If so use one of these.
If not and you are not comfortable taking off the front of the consumer unit (switch off the main switch but remember the wires to the top of the switch will still be live) then use a metal pipe or back box as near the CU as possible.

One other question - so far, I have replaced a few switches with metal ones, connecting the available earth to the earth terminal on the metal back-box. Then running a new bit of insulated cable from the earth terminal on the back-box to the earth terminal on the switch...I've done this wrong haven't I? I should have connected the available earth to the switch, then run a new bit of insulated cable back to the back-box terminal. But...does it matter, or should I re-do them?

It would be better to connect the CPC (earth wire) to the switch first but doesn't really matter.

 

[dk1uk]

Thank you for the replies, I'll give this a try and hopefully I'll see some continuity. Thanks again.

 

[dk1uk]

It would be better to connect the CPC (earth wire) to the switch first but doesn't really matter.

Quick check - is this the same for sockets?

 

[EFLImpudence]

Yes, because the metal faceplate must be earthed.

The back-box does not have to be, as it will be when the screws are fitted (if one of the lugs is solid), but it is good practice.