When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of screws
that could be 'fingered'.

On 11/02/2014 23:02, R D S wrote:
On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of screws
that could be 'fingered'.


Aren't the screws shrouded in plastic on the inside?

On Tue, 11 Feb 2014 23:10:53 +0000, GB wrote:

On 11/02/2014 23:02, R D S wrote:
On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no
earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of
screws that could be 'fingered'.


Aren't the screws shrouded in plastic on the inside?

Yeah, but the screws are metal and i'm pretty sure there's a metal track
between them.
If the live wire came unattached from it's terminal it could potentially
cause danger.
Not that i'm concerned, just surprised.

On Tue, 11 Feb 2014 23:25:01 +0000, R D S wrote:

On Tue, 11 Feb 2014 23:10:53 +0000, GB wrote:

On 11/02/2014 23:02, R D S wrote:
On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no
earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of
screws that could be 'fingered'.


Aren't the screws shrouded in plastic on the inside?

Yeah, but the screws are metal and i'm pretty sure there's a metal track
between them.
If the live wire came unattached from it's terminal it could potentially
cause danger.
Not that i'm concerned, just surprised.

In a possible answer to my own question...

The screws appear well contained and i'm guessing that modern switches
don't have the conductive track between the screw holes.

On 11/02/2014 23:02, R D S wrote:
On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of screws
that could be 'fingered'.

Many shallow plastic pattresses include a terminal for "parking" the earth.

There should be limited scope for the screws becoming live - and even if
they were they pose a limited shock risk since you can't easily get a
hold of them!


--
Cheers,

John.

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In article , John Rumm
wrote:
On 11/02/2014 23:02, R D S wrote:
On Tue, 11 Feb 2014 22:56:52 +0000, GB wrote:

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no
earth.

How come?

Ta.



What were you planning to earth?

Or do you just want to have a terminal to connect two earth wires?

Metal switches have an earth terminal, as do metal back boxes.

I'm just a bit surprised that plastic switch/boxes have no earth
protection, after all there is a live wire in there and a pair of
screws that could be 'fingered'.

Many shallow plastic pattresses include a terminal for "parking" the
earth.

Certainly the one I fiited on Monday had one.

There should be limited scope for the screws becoming live - and even if
they were they pose a limited shock risk since you can't easily get a
hold of them!

--
From KT24

Using a RISC OS computer running v5.18

On 12/02/2014 00:06, John Rumm wrote:

Many shallow plastic pattresses include a terminal for "parking" the earth.

Yes, although dry-lining boxes are usually sold without this. There is
a place for an earth terminal in the moulding though, and the terminals
are (I presume) available separately.

And it's not just for parking - you may need to join the CPCs of two or
more cables - e.g. where you have a 2+E 'switch drop' and a 3+E cable
going off to a second 2-way switch.

There should be limited scope for the screws becoming live - and even if
they were they pose a limited shock risk since you can't easily get a
hold of them!

Exactly so. There is a specific exemption in the wiring regs (BS 7671):

410.3.9 The provision for fault protection may be omitted for the
following equipment: [...]

(iii) Exposed-conductive-parts which, owing to their reduced dimensions
(approximate maximum of 50 mm x 50 mm) or their disposition, cannot be
gripped or come into significant contact with a part of the human body
and provided that connection with a protective conductor could only be
made with difficulty or would be unreliable.

NOTE: This exemption applies, for example, to bolts, rivets, nameplates,
cable clips, screws and other fixings.


--
Andy

On 12/02/2014 15:15, Andy Wade wrote:
On 12/02/2014 00:06, John Rumm wrote:

Many shallow plastic pattresses include a terminal for "parking" the
earth.

Yes, although dry-lining boxes are usually sold without this. There is
a place for an earth terminal in the moulding though, and the terminals
are (I presume) available separately.

Don't think I have ever seen anyone selling them... Lump of chockie
block seems the common solution! (although a wago would be my choice for
CPC continuity these days)

And it's not just for parking - you may need to join the CPCs of two or
more cables - e.g. where you have a 2+E 'switch drop' and a 3+E cable
going off to a second 2-way switch.

Indeed, (I did mentioned that in a previous post, but CBA to repeat ;-)

There should be limited scope for the screws becoming live - and even if
they were they pose a limited shock risk since you can't easily get a
hold of them!

Exactly so. There is a specific exemption in the wiring regs (BS 7671):

410.3.9 The provision for fault protection may be omitted for the
following equipment: [...]

(iii) Exposed-conductive-parts which, owing to their reduced dimensions
(approximate maximum of 50 mm x 50 mm) or their disposition, cannot be
gripped or come into significant contact with a part of the human body
and provided that connection with a protective conductor could only be
made with difficulty or would be unreliable.

NOTE: This exemption applies, for example, to bolts, rivets, nameplates,
cable clips, screws and other fixings.

The contact pins in a traditional BC lamp holder would be another good
example...


--
Cheers,

John.

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On Wed, 12 Feb 2014 15:15:05 +0000, Andy Wade wrote:


(iii) Exposed-conductive-parts which, owing to their reduced dimensions
(approximate maximum of 50 mm x 50 mm) or their disposition, cannot be
gripped or come into significant contact with a part of the human body
and provided that connection with a protective conductor could only be
made with difficulty or would be unreliable.


Given the times that we live in, this surprises me.

I was looking at a back box today and with 12mm plasterboard there is a a
few mm of bare metal screw that could (quite unlikely I know) come into
contact with a live.
And yes, it would be moderately difficult to get a good contact between
finger and screw, and then you could only prod it and not get a grip on
it.
But as there's always an earth available it baffles me that the usually
overly safety obsessed nannies have decided that we don't need to bother
with it.

In fact it's created a minor inconvenience.

In message , R D S writes
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.
Presumably because they are non-conducting
--
bert

On Tue, 11 Feb 2014 23:24:40 +0000, bert ] wrote:

In message , R D S writes
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.
Presumably because they are non-conducting

Nevertheless, afair, the plastic backboxes have an earth terminal
post to allow metal switch plates to be earthed[1]. The plastic switch
plates don't need this protection and the screws are quite well
isolated from possible contact with the live once fitted.

There might be a slight risk when removing the plate but the lighting
circuit fuse should be pulled out when doing this sort of work anyway
so even this risk doesn't matter. If you're going to test whilst the
switch plate is unscrewed from the backplate, the screws will be
absent and you'll be mindful of other safety concerns anyway (like not
poking your fingers into the wiring).

In short, there's absolutely no need to earth the fixing screws on a
plastic switchplate (and an earth terminal post is available to
connect a metal switch plate to the safety earth in accordance to the
regulations).

[1] It's been a while since I last looked at the backside of a plastic
backbox but I think I've seen some designs were the faceplate screw
thread inserts are rivetted to a track which joins to the earth
terminal post (which would guarantee that a metal switchplate, once
installed, will be automatically earthed via the fixing screws without
the need for a seperate earth strap connection).
--
Regards, J B Good

In article ,
Johny B Good wrote:
On Tue, 11 Feb 2014 23:24:40 +0000, bert ] wrote:

In message , R D S writes
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.
Presumably because they are non-conducting

Nevertheless, afair, the plastic backboxes have an earth terminal
post to allow metal switch plates to be earthed[1]. The plastic switch
plates don't need this protection and the screws are quite well
isolated from possible contact with the live once fitted.

There might be a slight risk when removing the plate but the lighting
circuit fuse should be pulled out when doing this sort of work anyway
so even this risk doesn't matter. If you're going to test whilst the
switch plate is unscrewed from the backplate, the screws will be
absent and you'll be mindful of other safety concerns anyway (like not
poking your fingers into the wiring).

In short, there's absolutely no need to earth the fixing screws on a
plastic switchplate (and an earth terminal post is available to
connect a metal switch plate to the safety earth in accordance to the
regulations).

When I re-wired my house (new to me) in 1965, the Electricity Board checked
the earth on all screws including light swtches.

--
From KT24

Using a RISC OS computer running v5.18

In article ,
R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

Nothing to earth? But the dry lining box should have a terminal to make
off the earth to - there for later use if the switch is changed to metal.

--
*A fool and his money are soon partying *

Dave Plowman London SW
To e-mail, change noise into sound.

On 11/02/2014 22:54, R D S wrote:
When using plastic switches and a dry lining back box there's no earth.

How come?

cos they are plastic ;-) (the chances of them becoming live due to fault
conditions are limited to slim and fat)

(the earth will still be present in the cables - that should be
terminated somewhere to preserve continuity and keep it out of the way)


--
Cheers,

John.

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Well maybe you are not supposed to use the plastic boxes?
I suppose if you really wanted to earth them you could achieve it with a
bit ofwire and a tag.
I would not use a plastic box for a dimmer, I've come a cropper that way
too many times in the past when the metal plate got shorted internally.
I guess plastic dimmers are much safer!

Brian

--
From the Sofa of Brian Gaff Reply address is active
"R D S" wrote in message
...
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.

In article ,
Brian_Gaff wrote:
Well maybe you are not supposed to use the plastic boxes?
I suppose if you really wanted to earth them you could achieve it with a
bit ofwire and a tag.
I would not use a plastic box for a dimmer, I've come a cropper that way
too many times in the past when the metal plate got shorted internally.
I guess plastic dimmers are much safer!

All the modern metal plate switches etc I've seen have an earth terminal
on them. So they could safely be fitted in a plastic box.

--
*Wrinkled was not one of the things I wanted to be when I grew up

Dave Plowman London SW
To e-mail, change noise into sound.

On 12/02/2014 15:22, Dave Plowman (News) wrote:
In article ,
Brian_Gaff wrote:
Well maybe you are not supposed to use the plastic boxes?
I suppose if you really wanted to earth them you could achieve it with a
bit ofwire and a tag.
I would not use a plastic box for a dimmer, I've come a cropper that way
too many times in the past when the metal plate got shorted internally.
I guess plastic dimmers are much safer!

All the modern metal plate switches etc I've seen have an earth terminal
on them. So they could safely be fitted in a plastic box.

I think its a pretty safe bet that if the accessory requires earthing,
it will included a dedicated terminal (or two) for the purpose.


--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
John Rumm wrote:
All the modern metal plate switches etc I've seen have an earth
terminal on them. So they could safely be fitted in a plastic box.

I think its a pretty safe bet that if the accessory requires earthing,
it will included a dedicated terminal (or two) for the purpose.


They do now - but it wasn't always the case. ISTR earth terminals for grid
switches being an optional extra.

--
*'Progress' and 'Change' are not synonyms.

Dave Plowman London SW
To e-mail, change noise into sound.

"R D S" wrote in message
...
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.

The reason anything is earthed is so that it cannot be at any voltage above
the general mass of the ground, ie you can't get an electric shock.
But if there's nothing metal to touch, there's nothing to earth.

Exceptions are made, where no earth is needed.
Eg double insulated (two layers of insulation)
All insulated. (Nothing metal to touch)

On 12/02/2014 18:27, harryagain wrote:
"R D S" wrote in message
...
When using plastic switches and a dry lining back box there's no earth.

How come?

Ta.

The reason anything is earthed is so that it cannot be at any voltage above
the general mass of the ground, ie you can't get an electric shock.

If one were being a pedant, you could highlight that limiting voltage
rise is indeed a fortuitous effect of earthing, but not its prime
purpose. Its earthed to ensure rapid disconnection of the supply. (if
you think about it, the best earthing is likely to achieve at the point
of a fault is limiting the voltage to about half mains)

But if there's nothing metal to touch, there's nothing to earth.

Exceptions are made, where no earth is needed.
Eg double insulated (two layers of insulation)
All insulated. (Nothing metal to touch)




--
Cheers,

John.

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