metal light switch

[Iggifer]

Does it? Didn't, and not sure I can, see that.

I think we'll both agree the lug on the left is adjustable and the lug on the right, which you can't quite see properly, appears to be an adjustable, based on the form of the bend you can just about make out. It would normally be bent the other way for a fixed lug

 

[ban-all-sheds]

Hmm - does look like it. CTRL++++++++ is your friend. Ho hum.

Does the "fixed lug" requirement relate to earthing a back box via the switch faceplate, or earthing the faceplate via the back box?

 

[Iggifer]

Off the top of my head I’d say backbox from switchplate - only based on the fact you’d take a socket earth to the socket first and then earth the backbox. You’d be mad to do I the other way for sockets.

It doesn’t REALLY matter so long as both are suitably earthed.

 

[JohnW2]

I think we'll both agree the lug on the left is adjustable and the lug on the right, which you can't quite see properly, appears to be an adjustable, based on the form of the bend you can just about make out.

We are always hearing about this 'fixed lug' requirement for omission of an explicit conductor earthing the back box, but, although it makes some sense, I wonder where this 'requirement' actually comes from?

If one feels that the back box must be earthed (which I suppose is desirable, because of the screws, in the case of a non-metal accessory), I'm no great fan of reliance on the faceplate screws, no matter what the nature of the lug, since the quality of the connection is, even with a fixed lug, dependent upon how well the screw is tightened. However, I suppose it could be said, conversely, that if one is assuming adequate tightening of the screws, then the quality of the connection is probably similar with a fixed or adjustable (metal) lug.

Kind Regards, John

 

[bernardgreen]

It is simple common sense.

99.99 % of time the switch plate is preventing a person touching the back box. 0.01 % of time the back box is exposed by removal of the switch,

9999 reasons to connect CPC to switch plate and only 1 reason to connect the CPC to the back box.

 

[JohnW2]

It is simple common sense.

That I know (even though some may disagree).

My question is whether this often-mentioned 'requirement' is actually 'required' by anything formal.

Kind Regards, John

 

[DetlefSchmitz]

We are always hearing about this 'fixed lug' requirement for omission of an explicit conductor earthing the back box, but, although it makes some sense, I wonder where this 'requirement' actually comes from?

...a NICEIC guidance booklet...

 

[JohnW2]

...a NICEIC guidance booklet...

I feared as much

Kind Regards, John

 

[Deleted member 18243]

You can't have too many earths.

 

[John D v2.0]

You can't have too many earths.

Nooooooooo don't start that argument again!!!

Anyway just to distract people, OP: the old switch looks like it was also likely to be class I so you probably should have had it earthed the whole time, lucky you're changing it, now you can do it properly.

 

[ban-all-sheds]

Off the top of my head I’d say backbox from switchplate - only based on the fact you’d take a socket earth to the socket first and then earth the backbox. You’d be mad to do I the other way for sockets.

Unless the regulation (someone must know the number, and yes I freely admit that right now I CBA to try and find it) dates back to the days when it was common to use conduit as the cpc (this is a light switch, remember), in which case it might be quite reasonable to say that with one fixed lug you didn't need a flylead to the switch. Then again, those were the days when you didn't need a cpc at all for lighting.

So I dunno.

It doesn’t REALLY matter so long as both are suitably earthed.

Indeed.

But as for "suitably", I'm not convinced that a back-box is an exposed-conductive-part: Conductive part of equipment which can be touched and which is not normally live, but which can become live under fault conditions.

How can you touch a back box?

99.99 % of time the switch plate is preventing a person touching the back box. 0.01 % of time the back box is exposed by removal of the switch,

9999 reasons to connect CPC to switch plate and only 1 reason to connect the CPC to the back box.

Except that during that 0.01% of the time the circuit should be isolated...

 

[ban-all-sheds]

...a NICEIC guidance booklet...

Oh well ignore the above about a reg number.

One of these days I'll learn to read all the unread posts before replying, especially when they are all on one page....

 

[ban-all-sheds]

And to spare my blushes the Mods have removed the post I should apologise for

 

[JohnW2]

Nooooooooo don't start that argument again!!!

I imagine that the argument didn't "start again" because others, like myself, took the comment to mean that one "can't have too many" earth connections to something that needs to be earthed!

On another point, whilst it can easily be argued that a back box is not (at least, should not be!) an exposed-c-p, I would think that the faceplate screws certainly are and, as I've said before, that becomes particularly relevant with a non-metallic faceplate.

Kind Regards, John

 

[mwatsonxx]

It is simple common sense.

99.99 % of time the switch plate is preventing a person touching the back box. 0.01 % of time the back box is exposed by removal of the switch,

9999 reasons to connect CPC to switch plate and only 1 reason to connect the CPC to the back box.

It is lack of common sense.

First you have to accept that the UK has a crap domestic T&E wiring system. The only reliable method of terminating cables in metal boxes is to rely on the plaster holding the cables in place. In the absense of plaster in a partition wall there are no cable fixings, in fact the only fixed part is the cable L N and E connections. So there is a great possibility of the steel box cutting into the inner and outer cable sheath, and that is why the boxes should be permanently connected to earth with flying leads to face plates.

Also, if the main earth connection is made to the face plate, the connection to the steel box (and remaining parts of the circuit) will be broken when the plate is removed. And that is how the live steel box could kill someone.

Fixing screws used as earth connections are a dangerous nonsense.