Why are light switches not earthed?

[Dave Plowman (News)]

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.

[John Rumm]

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)

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

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

[John Rumm]

If you look at TLCs "ultimate" range, (made by GET/Snider) they include that for all their accessories. Makes the sockets look nice and neat)

[John Rumm]

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

[charles]

"schneider">

Interestingly, I have just had to replace a double 13A socket of theirs since the switch failed OFF - although it had been permanently ON for the last 2 years.

[Andy Wade]

Err, no, that's an example of the different exemption in 416.2.4 - live parts accessible without the use of a tool or interlock. The 'screw earthing exemption' of 410.3.9 (iii) concerns accessible conductive parts which should only be live in the case of a fault (i.e. failure or bridging of basic insulation).

The former is concerned with basic protection (formerly direct contact) and the latter with fault protection (indirect contact). In both cases the risk is deemed acceptable due to the small contact area - so same principle, different situation.

Another difference is that 416.2.4 applies to four very specific cases meeting defined standards while 410.3.9 (iii) is more open to interpretation...

[Andy Wade]

On 12/02/2014 17:17, Andy Wade wrote: [snip]

PS here are some dry-lining box earth terminals:

(p.4 Dry lining accessories).

[Dave Plowman (News)]

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

[harryagain]

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)

[R D S]

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.

[Bill Wright]

Andy, do you read these rule books the same way as other people read novels?

Bill

[John Rumm]

Yes accepted, different regs and different situations, but the point about small contact area was what I was getting at...

[John Rumm]

Don't think I have ever used Appleby... I did note that many of the new "fire and noise spread" prevention dry lining boxes have them though.

[John Rumm]

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)