Socket Safety Question

[Zuru67]

Hi,

I am replacing some light sockets and power sockets at home and having initially looked at one of the wall single switches I can see that the faceplate (plastic) is not earthed, but the incoming supply has an earth which is terminated into the metal back box.

The new face plates that I have purchased state that they they need to be earthed and have a standard screw down earth point on the back. I dont seem to have enough room on the back box earth point to add an earth between the back and the new faceplate.

What can I do?

Thanks

Adam

 

[JohnW2]

... I can see that the faceplate (plastic) is not earthed, but the incoming supply has an earth which is terminated into the metal back box. ... The new face plates that I have purchased state that they they need to be earthed and have a standard screw down earth point on the back. I dont seem to have enough room on the back box earth point to add an earth between the back and the new faceplate.

What do you mean by 'not enough room'? If you mean that the existing earth conductor will not reach the faceplate, you can add a new bit of (green/yellow sleeved) wire between the back box terminal and the face plate.

Kind Regards, John

 

[Zuru67]

Hi John,

I mean that the terminal where the existing earth is connected from the incoming feed to the back box is too small to have another piece of 6491X to be fitted into it, there is no room.

Cheers

adam

 

[JohnW2]

Hi John, I mean that the terminal where the existing earth is connected from the incoming feed to the back box is too small to have another piece of 6491X to be fitted into it, there is no room.

That's surprising. What size (CSA) of 6491X are you trying to use? You only need a conductor of the same size (CSA) as that of the CPC ('earth') of the supplying cable (probably 1mm² CPC at light switches, 1.5mm² at sockets). The usual thing to do is to use a bit of (bare) CPC from T+E cable of the appropriate size and sleeve it with G/Y sleeving.

Kind Regards, John

 

[Zuru67]

The T+E was installed in 1998 the earth is quite large and screwed into the earthing point on the back box. I need to run a piece of 6491X or similar from the back box to the front plate. I was looking at using 1.5mm2 but it seems the T+E was more like a 4mm which is why the earth connector on the back box is unable to take another cable.

Seems the sparks working for barrett didn't fancy installing a normal sized cable.

 

[JohnD]

4mm? For a light switch? Is it stranded?

Or do you mean for the socket?

Put the big cable in the socket, and run a flylead to the backbox.

 

[Zuru67]

I was quite surprised at the conductor size John, but hey

I will reverse the way and as you say run the main to the face plate and run a small 1.5 back to the back box.

Cheers

adam

 

[Taylortwocities]

Does the metal back box have one lug that is fixed?
If so there is no requirement to run a link to the back box, you can just terminate on the faceplate and leave it at that.

 

[ericmark]

Please remember I have not seen the box so there is a little guess work. It would seem you have a radial system with imperial with 7/029 or 7/036 cable?

The old system does not fully integrate with new and one has to be careful it has not been extended with new size cable.

Question one has to be is this a ring or a radial as the answers will be very different. Was it a complete re-wire or part re-wire?

It is very easy to jump to what should be done with a post 2008 installation but pre 2008 the rules were different and pre 2001 very different.

The 3.5mm screws which hold the socket to the back box will normally ensure that an earth be it to back box or to socket will earth both units. As long as when you plug in the earth loop impedance meter it reads less than 1.44Ω (assuming a B32 MCB) then there is no problem.

Inspecting and testing is the b all and end all of any installation. Without the readings it is by the grace of god and it does not matter what wire goes to what it is all down to the inspection and testing.

Although the professional test set is expensive the

plug in tester costs around £42 which compared with a proper earth loop impedance tester is very cheap.

Of course for any new circuit you should also test the RCD both for tripping current and time but I would agree the £75 to hire a test set is expensive. That is if you know how to use it.

 

[JohnW2]

Please remember I have not seen the box so there is a little guess work. It would seem you have a radial system with imperial with 7/029 or 7/036 cable? ... Question one has to be is this a ring or a radial as the answers will be very different.

The OP may have got his wording slightly wring but (surprising though it may be), he appeared to be talking about a light switch, not a socket. John D asked for clarification, but we haven't yet had a totally explicot response.

The 3.5mm screws which hold the socket to the back box will normally ensure that an earth be it to back box or to socket will earth both units. As long as when you plug in the earth loop impedance meter it reads less than 1.44Ω (assuming a B32 MCB) then there is no problem.

I would be fairly (but not totally) comfortable if the socket were explicitly connected to the CPC and the back box was earthed via the faceplate screws, but would you consider the converse to be acceptable (no CPC connection to socket, earthing of it being via back box and screws), even if the loop impedance was acceptable? [BTW the Martindale tester you portray would, of course, have to read 0&#937; for one to know that the loop impedance was <1.44&#937;, since the next option up is 1.7&#937;].

Kind Regards, John

 

[JohnW2]

Does the metal back box have one lug that is fixed? If so there is no requirement to run a link to the back box, you can just terminate on the faceplate and leave it at that.

As I've just asked eric in response to his comment, are you happy with that 'both ways around'? In other words, would you be happy, and regard it as acceptable, for the only earth connection to the socket being via the back box and the faceplate screws? (I don't think I would!).

Kind Regards, John

 

[Taylortwocities]

My response was based on the OP saying

having initially looked at one of the wall single switches I can see that the faceplate (plastic) is not earthed, but the incoming supply has an earth which is terminated into the metal back box.

The new face plates that I have purchased state that they they need to be earthed and have a standard screw down earth point on the back.

There is no suggestion that his query relates to sockets, only light switches.

 

[JohnW2]

My response was based on the OP saying ... There is no suggestion that his query relates to sockets, only light switches.

Fair enough - and, of course, is exactly what I wrote to eric last night. However, there is no doubt that the OP is in the process of replacing the face plates of both sockets and light switches - so, although it's not actually what the OP wrote, I suppose it's just possible that eric's apparent 'assumption' could be right.

Assuming that it is a lighting circuit, it is, of course, possible that there was originally no CPC in the cables of the circuit and that a separate CPC was subsequently added, using 4mm² singles.

Whatever, do I take it that (like me) you disagree with what eric was saying/implying [namely that, if it were a socket, then it would be acceptable (or, at least, conducive with 'sleeping at night'!) for the CPC to be connected to the socket only via faceplate screws?] -- I think the intent of eric's words was clear, given that he included a picture of a plug-in tester.

Kind Regards, John

 

[Taylortwocities]

I agree with you wrt sockets. Earth must be permanent wired connection to the socket's earth terminal.

 

[JohnW2]

I agree with you wrt sockets. Earth must be permanent wired connection to the socket's earth terminal.

Thanks for confirming. I'm glad to hear that you agree with me!

Kind Regards, John