3-wire light switch for home automation

[dpm_dpmartin]

Evening all,

I've been getting into Z-Wave home automation recently - so far only using some multi-sensors and some power socket switches. I also wanted to update my living room light switch to be controllable via the system.

It's just a 1-way, 1-gang, on-off switch that controls a single light fitting... the simplest thing ever.

The place I'm buying my kit off (Vesternet, very good) have told me that I need to have a neutral at the switch to use a smart switch / relay. I absolutely understand how this works, it's all explained on this page.

http://www.vesternet.com/blog/2014/09/why-smart-switches-cant-be-used-without-neutral/

I gather if I pull the light switch off the wall and find only 2 wires in there then only a dimmer solution will work. I wanted to ask... why doesn't the UK have neutral at the switch as a standard - I'm guessing, as someone made these smart switches to sell, that some other places must do this as a matter of course?

Appreciate any insight... I thought being able to control my simple living room light would be easy... nothing ever is.

Is retro-fitting neutral at the switch even remotely possible in something that's not a new build? I mean, am I talking nonsense (probably)?

 

[Iggifer]

There's two (common) ways of wiring lighting circuits. Looping the neutral at the switch, i.e you take your feed in, feed out and switch wire to the switch. This makes the use of this kind of gear easier, but it also means you have multiple cables in a switch box.

The other way is to take the neutrals to the light fitting (rose) or a junction box in the ceiling, then just taking a switch wire (live + switched live) to the switch.

Looping at the switch is becoming more common as junction boxes are falling out of favour (it has been used for a while but is pretty much the de facto way to wire lighting circuits now).

You can take a neutral to your switch, you will either need to re-arrange the whole part of the circuit (not ideal) or replace the switch wire for a 3 core+earth, which would contain your neutral, and L+SL

 

[dpm_dpmartin]

Is "taking a neutral to my switch" by replacing the switch wire a mammoth job for someone? Does it then require changes at the light fitting side or not? Are we talking about chasing out walls and replastering and all that malarky?

Basically, is it all a pipe dream and I'd be better getting dimmable LED bulbs (5 are in the fitting) and a dimmer module instead of a relay?

If I put a dimmer module behind the switch, I don't even know if I need to change the existing switch or whether I can still use it, even though that's not a dimmer itself.

I did not think this aspect would be so tricky.

BTW, I took the switch off the wall... 3 wires only, 1 is earth.

 

[Iggifer]

Chances are it would involve some chasing out. But you would just replace one cable from the existing light to the switch, not a major job, but the chances of being able to pull a 3 core through where the switch wire is now, without any damage is pretty slim.

Are you talking about the Z-Wave 2-wire dimmer modules on the same site? It's a little deceptive of them, as it says "very small size, enables modules to fit into standard backbox (45mm recommended) 45mm is FAR from standard. For starters, the box would be 47mm if it was a standard steel box (small issue) and more importantly, if you've only got one switch there, it's likely to be a 16mm or 25mm backbox.

Chances are it wouldn't fit, so you would need to chop a deeper box in - not a great deal less messy than a whole new cable

 

[dpm_dpmartin]

Agreed. The depth of the box appeared to be less than 30mm to me.

 

[Iggifer]

Yea it's probably a 25mm. 16mm is very slim.

You can get spacers, but they look naff

 

[ericmark]

It you loop in switch it means longer cable run and the loop impedance is higher also there is no permanent line at ceiling rose so wiring emergency lights and ceiling fans is much harder.

If you loop at ceiling rose it means no neutral at switch in most cases but lack on permanent line at ceiling rose can assist when wiring in voltage droppers for 12 volt lighting.

So 6 of one and half dozen of the other there are for's and against's for each method. As far as automatic lighting using sensors in the ceiling often works better than sensors in the wall so British method is in the main better using the standard ceiling rose method.

 

[bernardgreen]

Despite the salesmen saying it is easy to retrofit home automation onto existing wiring the simple fact is that fitting home automation to a standard domestic electrical system is far from being straight forward and can be a nightmare in some situations.

If you are going to "automate" the house then a rewire of the lighting is almost always the only way to get it working properly.

 

[dpm_dpmartin]

As far as automatic lighting using sensors in the ceiling often works better than sensors in the wall so British method is in the main better using the standard ceiling rose method.

Hi, it's not a sensor, but rather a relay that can be controlled wirelessly via a home automation system, so it's not just for automatic lighting but schedules and logic and suchlike. You can tie that logic into other sensors, certainly.

 

[dpm_dpmartin]

If you are going to "automate" the house then a rewire of the lighting is almost always the only way to get it working properly.

Lighting does seem to be the stumbling block. Power and sensors are all easy. Maybe I'll make do with lamps.

 

[bernardgreen]

Maybe I'll make do with lamps.

That does provide "automated" lighting in a fairly easy way. It also leaves the "non automated" lamps in the ceiling working normally on a normal switch.
That is a very useful fall back for when
[1] the remote control cannot be found or it has a flat battery
[2] the wireless channel is blocked
[3] you have visitors who cannot understand how to operate the "automation" system controls

 

[JohnW2]

It you loop in switch it means longer cable run and the loop impedance is higher ....

Is that necessarily the case? It surely depends upon the relative positions of the switches and relative positions of the lights/fittings, doesn't it?

Kind Regards, John

 

[EFLImpudence]

Lighting does seem to be the stumbling block. Power and sensors are all easy. Maybe I'll make do with lamps.

There is, of course, the point that when initially designing a circuit with remotely operated switches, they would not be placed by the door, would they?

 

[ban-all-sheds]

Put them next door.

Drive your neighbour mad.

 

[bernardgreen]

I know one chap who did program a remote control to be recognised by his neighbours excessively bright gerden floodlight. Neighbour never did realise what was happening, he believed it switch of when it was over heating