Understand switch wiring

Sandtree

We’ve a 3 gang switch controlling 3 areas of lights all on a one way basis. Have considered replacing it with a smart switch and so unscrewed the existing switch to check for a neutral (out of picture) but confused by the wiring which hopefully someone can make sense of…



Each switch has a single wire into its “common” from the wall. Two of the switches are connected on the “1 way” to the wall, the third however is connected to the other two “1 way” and nothing from the wall. There are 5 cables coming from the wall each 2 core plus bare earth. 

Guessing it’s just wired backwards but is anything else going on?

FreeBear

All the "1 way" terminals are linked, so I would surmise that these are your live feeds. The wires going in to the "common" terminals would go off to the light fittings - This can be checked fairly easily with a multimeter. Just don't use those electrical "screwdrivers" or pens that supposedly light up when in contact with a live wire.

If you have a neutral feed in the back box, you can avoid using those smart switches that claim to be "no neutral" - By all counts, some bulbs will flicker. Also check your back box depth. You'll need a 35mm deep box minimum to allow for the switch & wiring.

P.S. I have a preference for the Sonoff (and knock-offs) as they can be flashed with open source firmware. No need to rely on a cloud server being on line for ever more (also steer away from Tuya - the firmware is a pig to flash).

Risteard

That is a Class I switch and must be Earthed with the terminal provided.

Sandtree

Risteard said:

That is a Class I switch and must be Earthed with the terminal provided.

It’s on a metal back box which is earthed… is that ok?

FreeBear

Sandtree said:

Risteard said:

That is a Class I switch and must be Earthed with the terminal provided.

It’s on a metal back box which is earthed… is that ok?

There should be a short length of (sleeved) earth wire between the terminal on the switch and the back box. Relying on a metal screw & contact between the various metal parts is not "up to code". But if you are replacing with a smart switch (plastic & glass construction), the lack of earth is irrelevant.

Risteard

Sandtree said:

Risteard said:

That is a Class I switch and must be Earthed with the terminal provided.

It’s on a metal back box which is earthed… is that ok?

No, it isn't OK.

Ectophile

The earth would normally go to the switch.  So then the back box becomes earthed when you screw it on.  The way it's done now isn't right.  Either move the earth to the switch, or wire an earth from the back box to the switch. Earthing the back box from the switch is acceptable, provided that one of the lugs that the screw goes into is fixed, rather than "floating".

Sandtree

Ectophile said:

The earth would normally go to the switch.  So then the back box becomes earthed when you screw it on.  The way it's done now isn't right.  Either move the earth to the switch, or wire an earth from the back box to the switch. Earthing the back box from the switch is acceptable, provided that one of the lugs that the screw goes into is fixed, rather than "floating".

The lug on the earth side is fixed/part of the box, the one on the other side is clipped in/not part of the box which I assume you mean by floating.

On a related question... my preferred brand doesnt officially support the UK market with their switch but has released one for the Australian market which has the same 230/240 @ 50hz as the UK but their "single gang" is a longer/thinner backbox than the UK's square. Is there any issues with deviating from UK standard dimensions etc? I have seen old posts on some other device which says code doesnt specify but I realise these things change

FreeBear

Sandtree said: On a related question... my preferred brand doesnt officially support the UK market with their switch but has released one for the Australian market which has the same 230/240 @ 50hz as the UK but their "single gang" is a longer/thinner backbox than the UK's square.

Do they do one for the EU market ?

If they do, the only difference will be the fixing screw size (M4 for the EU, M3.5 for the UK). Buy a pack of screws from somewhere like Toolstation. If you are buying from overseas, don't forget to factor in shipping costs and the possibility of import duties.

Sandtree

FreeBear said:

Sandtree said: On a related question... my preferred brand doesnt officially support the UK market with their switch but has released one for the Australian market which has the same 230/240 @ 50hz as the UK but their "single gang" is a longer/thinner backbox than the UK's square.

Do they do one for the EU market ?

If they do, the only difference will be the fixing screw size (M4 for the EU, M3.5 for the UK). Buy a pack of screws from somewhere like Toolstation. If you are buying from overseas, don't forget to factor in shipping costs and the possibility of import duties.

No, US and Australia only for this particular device... the plastic surround varies between these two markets but the size of the back of the device can be constant. Not sure when a UK market version will appear as they need to reduce the width of the back of the device by whatever the average size lugs are on backboxes + 1mm which inevitably will be a whole redesign of the electronics.

Have been looking at market places (Amazon, eBay etc) and as well under £135 in cost it means all import costs are included in the price. 

Was more concerned if regs require either specific dimensions or certain BS standards etc that something from downunder may not comply with

Ectophile

It depends what issues you care about.  If an accessory is designed for 230V AC, and comes from a reputable manufacturer, then it's unlikely to be unsafe.

But the UK "Wiring Regulations" * expect you to use accessories that meet UK or harmonised European standards.  Anything else is a "departure" and needs to be justified.

* Despite the name, they aren't actually law.  It's the traditional name for what's now BS7671.  But some laws do call up BS7671.