The Australian and British electrical standards are very similar. We too have the neutral and earth bonded at the main switchboard, and we too have an earth electrode in the ground connected to this earth. That does not take away the fact that the earth (ie: all metallic items in your house that are electrically connected) could become live in the event of a fault. I know first hand because I have been called out to rectify such instances.
Sure we don’t have fused plugs but that’s a part of the appliance, not the building wiring. Without digging it up (I do have a copy of the British Wiring Code) I’m fairly certain that just like here in Australia, you are NOT to connect the protective earth as a load current path.
Have a look at the item I linked above for a safe way to monitor line voltage, or simply wire in devices where you do have access to a neutral. Sometimes it requires thinking outside the box, like installing a device in the ceiling above the light switch and using the wires that would normally switch the light as GPIO wires. Just because the wires are currently running at 240V doesn’t mean you can’t re-purpose them as 3.3V GPIO wires. I have done this in the past (my old house) where I couldn’t get a neutral to the switch. Instead I mounted the z-wave switch in the ceiling and used the switch wires in the wall to control the z-wave device via it’s input which runs at 3V.
Z-wave is a wireless protocol. There are heaps of different devices, sensors, switches, dimmers etc. Using one like this which requires a neutral wire would mean that unless you have (or can install) a neutral wire at your light switch, then you need to look at other options. A way around it is to install in in the ceiling space above the light switch / light and use the existing light switch wires as the control wires.
Here is a really dodgy sketch of how they are wired. The blue wires used between S1 and S2 would normally be the standard light switch wires, here they get used as the input / command / signal (whatever you want to call them) to the z-wave device.
This is just an example but in reality you could use an ESP and relay to switch the light, with the wires shown in blue going to a GPIO on the ESP.
I would point out Dave in the UK & ROI we use RCDs,
That wouldn’t in my case as its a 2 gang switch and the live feed to the switch is required.
I would not use Zwave as its a mesh system, and it immunity to nearby 2.3 GHz high power systems is poor. Apart from all the hash it radiates
Sorry @richard-g8jvm but we too use RCD’s in Australia. I don’t mean to sound nasty here but I don’t think you quite understand the circuit design I’m trying to explain. I really need to draw it to make it clearer which I’ll try and do later. But the point is that you change the existing light switch function over to a relay which is controlled by a device (it doesn’t need to be Z-Wave, that was simply an example. You can use ESP8266’s which are straight wifi) and that device is then given a signal by your physical light switch.
In your case with a 2 gang switch it would mean changing both switched circuits over to the ESP (or whatever device you choose) so that you only have ELV running down those switch wires
I do understand exactly what you have drawn, . You are assuming that you can get at the ceiling rose, and if you can the simplest solution as the switch cable is 1mm twin & E and the earth wire is not need on the switch unless you have a metal faceplate, if the switch is insulated, plastic or similar the earth wire is easily identifiable on the rose, its then just a case of disconnecting it , put a blue sleeve on it and connecting it to the neutral and then you have a neutral feed at the switch.
That is if you can get at the ceiling rose.
In my case the switch is for the central pendant light and a pair of wall lights, the switch cable
in my case 1.5mm 3+E may go to the ceiling rose, but that is sitting behind a 600mm plaster
ceiling decoration with just a two wire feed to the pendant lamp, or it may be to a junction box in the space above the ceiling, which mean lifting flooring upstairs to get at it, and thats large T+G chipboard, wich is an absolute bugger to get up in one piece.
When I can get at the plaster decor covering the rose I’ll look , but I fell off a ladder last Sunday and now have a couple of cracked ribs, so working with my arms raised is painful.
Changing the pattress behind the switch will also have to wait as that a hammer and chisel job, as thats brick behind it.
Working on the first floor is easy as its all dry wall and very easy to drop cables, the ground floor is all solid brick walls.
Once the Shelly-1 switches arrive, I can measure the standby current and the current when the relay in energised, and also check if the switch control status is reported back to the mqtt server, and then decide which way to proceed.
Ok, so if wiring is a real pain due to access then perhaps you are better off using wifi globes and leaving the light switches permanently on (so the globes always have power) and then switching them on and off by another means. I did this while in a rental (since I couldn’t modify wiring) and used Xiaomi wireless buttons which I stuck in place above the light switches. These provided local / physical control while also allowing HA to control the lights via automations or from the GUI. The bonus is that they are cheap and HA can be coded to provide 3 functions per button
Thats not the way I wish to proceed Dave, and BTW your circuit diagram is flawed, you have taken no account of EMI protection, something you should consider when connecting an antenna to the GPIO ports of a device which is inherently fast.
Given that I have successfully used that setup for a long time I think your radio background is causing you to over think this. The device I crudely sketched onto is designed to be inside a wall box with 240v and the magnetic fields present there. They are fine. Secondly, if using an ESP as I suggested, then filter circuitry can easily be included before hitting the GPIO.
Happy to leave it, but the case of illegal, it’s not my opinion, it’s the law. Perhaps you should invest in a copy of the British Wiring Standards, or use an electrician…
I have ordered a shelly pm1 which is rated for 16amp load and I received it today. To my surprise it doesn’t have any earth terminals which has put me off as I intended to use it for my water heater and it is rated at 16amp.
So in my case here in the UK and fault current wont be seen as such and my RCD wont trip. Surely a safety concern?
It doesn’t need an earth terminal.
your circuit is between live and neutral , you boiler is connected to the hot water/central heating .The pipework is bonded to earth and it will be at multiple points. the RCD will trip if
the leakage current exceeds 30mA either from live to earth or neutral to earth.
The Shelly-1 is nothing more than a switch .
On over current the MCB in the supply to the boiler will open , that just acts as a series fuse
HTH
What if there is a fault in the shelly itself ? I have a standard water heater no boiler nothing everything is electric in my apartment. So you can imagine the water heater with live neutral and earth which normally go to a time switch that has earth init
If there is a fault in the Shelly you are relying on the series fuse (MCB) to open.
I would be wary of using a Shelly with a 16A load, as the load you are connecting to will be fairly inductive.
Which means when the contacts on the relay open a back emf is produced,which wich cause an arc between the contacts, which will pit the surface of the contacts.
each time the contacts are opened and closed the pitting will get worse, and the relay will fail.
If you want to control a high current load , use the shelly to control a relay or contactor.
Use something that can switch 30A, then you have a good safety margin.
You can buy octal based relays that can switch 30A at 240Vac, and the bases have screw terminals. Dont buy Chinese relays , stick to a well known make like Omrom , I think CPC keep them in stock and you dont need an account.
The shelly then just becomes the controller for the relay, and should last a long time.
does that make sense ?
Yes indeed at present I have connected my water heater to sonoff th16 which has earth and all that. However I was thinking if upgrading it after hearing the faults which can be caused by the sonoff.
Mind you I have connected the sonoff th16 over a year now and have had no problems at all.
I’ve got 4 shelly s in the post to me, i’ll pull one apart when they arrive.
If there is an embossed little square one the casing of the shelly it indicates its double insulated
and no earth is required.
The big problem with switches is how people interpret the specification
when they say 16A they mean 16A maximum, , a bit like cars, if the speedometer is marked at
130mph, and you drive constantly at that speed , the engine wont last long.
a good rule of thumb is to only operate up to 50% of the current rating, maybe a bit more but not max rated
UK water heaters are usually 3KW, less than 16A, what connection do you have to the mains
on the other side of the time switch, plug and socket or a switch with fuse ?
