No Neutral light switches?

I'm not fitting one, but am curious as to how they work where the Neutral is not at the switch.

Essentially you add a capacitor between the SL & N at the light, so am I right in assuming that the capacitor allows the switch to see the Neutral through the Switched Live when the light is off?

Also, are these affected by using an LED lamp or do they only work with incandescent lamps?

muffking said:

am I right in assuming that the capacitor allows the switch to see the Neutral through the Switched Live when the light is off?

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Yes, you are right.

With incandescent lamps the relatively low resistance on the filament of the lamp allows the switch to see the "Neutral" via the Switched Live. LED drivers in lamps are much higher resistance and thus do not allow the switch to see enough "Neutral" for the switch to operate properly.

Some sources sell an expensive capacitor for this purpose

Or a more economical way, (*) although intended to suppress arcing when connected across switch contacts it also works as a snubber when connected across the lamp terminals. ( Switched Live and Neutral )


Capacitor 0.047uF micro Farads 250 volts AC in series with Resistor 100 ohms

Which come pre-packaged as a contact suppressor from RS Components

RS Stock No.206-7869
Mfr. Part No.PMR209ME6470M100R30
BrandKEMET

(*) £5 each but sold in packs of 5 ( £25 )

There are other sources

I used to get mine from Maplin at half that price

muffking said:

Also, are these affected by using an LED lamp or do they only work with incandescent lamps?

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The concept worked moderately well with incandescent lamps, although certainly wasn't perfect.

Using it with any modern lamp such as LED or fluorescent will open the door to a whole world of unpredictable and unfixable problems.

If you want such features, use devices with a neutral.
If the switch position doesn't have one, then fit the device at the light instead (such as the Shelley 1). Or rewire to include a neutral.

Thanks guys. I came across the diagram whilst searching for a smart FCU and it made me want to check how these no neutral switches work.

Any British light will since the switch wires do not run with a neutral will have some capacitance or inductive linking so unless the lamp has some circuit to allow a small amount of current to flow without switching it on will flash or light dim, a little like the 4 - 20 mA sensors used in industry all LED lights in the UK have to let a little current flow without lighting, how much however unlike the 4 - 20 mA is not laid down, so varies bulb to bulb, the switches normally state the load needs to be 5 watt minimum which one would expect means 5 watt total, however I have found bulbs under 5 watt even if 5 are used so total over 5 watt they don't seem to allow enough current to flow without a load capacitor. So G9 bulbs are a problem, but found GU10, E14, and BA22d bulbs work OK.
It seems there are two issues with LED bulbs, one is flashing when off, the other is a flicker when switched on, I am not sure what causes the flicker, when on, just know if bulbs over 5 watt are used it does not seem to happen, only bulbs under 5 watt seem to have a problem. I use wifi light switches without a neutral and they seem to have three problems.
Two already listed and as long as bulbs over 5 watt are used it seems to be avoided, clearly if the electronic switch dims the light as well, then if 50% dimming the bulb needs to be 10 watt so still 5 watt when dimmed. My electronic switches are simple on/off, the third problem seems to be EMC, using a couple of sockets and switches there was no problem, but as the number increased to 21 I started to get a problem with lights having a mind of their own, switching on/off when not set to switch on/off, so have needed to remove two light switches, this has resulted in a socket which was also doing it's own thing to start to behave its self.
The room with G9 bulbs has one quartz bulb, which seems to cure the flicker on all bulbs.
I use MiHome Energenie, there is also a forth problem, any power cut and the units remain off after power is switched back on, so when the plug in ceiling rose had a problem could not work out if it was the switch or ceiling rose, so fault finding is a problem, only way was to refit the flick switch until fault found.
But in general not had problems with BA22d bulbs, or E14 bulbs in a chandelier one has 5 the other 8 bulbs, did have a slight problem with GU10 but simply swapped bedroom bulbs with kitchen and flicker stopped, only the G9 required a 4 uf capacitor across bulbs, and even that only stopped it not switching off, it did not stop flicker, had to fit one quartz to stop flicker.

SMART ( when applied to home automation ) = Significant Money And Ragged Technology

bernardgreen said:

SMART ( when applied to home automation ) = Significant Money And Ragged Technology

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You are likely correct, it seems a mobile phone which connects to internet using cell sites is called smart, and anything which connects to that phone is also called smart, to my mind smart means some thing which works out what is required without you needing to manually select what it does is smart, so if the device monitors your phones and adjusts the home heating according to how far away you are, so as you travel home it increases the heat so that without exceeding the return temperature which would stop the boiler gaining the latent heat it allows the home to cool so saving energy, and then to reheat so it is still at the comfort zone when you return, that is smart.

However if you need to get phone out to alter the temperature, that is not smart, it is simple telemetry.

The problem is my devices can use IFTTT (If this then that) so a program can be written to make a non smart device work like a smart device, the device is not smart, the smart bit is in some computer connected to the internet, not in the actual switch, one can set up bottles of water and weights to random fire guns so the enemy thinks your still there, the smart bit was the guy who thought of the idea, the container with the hole in filled with water was not smart.

And one does wonder where the smart bit actually is? I had some problems, and to try and cure it, I turned off power, for some reason when the power was returned my thermostat did not connect to the router, I was not really worried about that, however came down in the morning to find central heating running, and the thermostat set to 20°C where the schedule was set for it to be at 17°C, it seems if the thermostat is not connected to internet the schedule is messed up, does not really matter if it gets time, or complete schedule from internet, it seems the thermostat is not very smart, that bit is some where else.

ericmark said:

so if the device monitors your phones and adjusts the home heating according to how far away you are, so as you travel home it increases the heat so that without exceeding the return temperature

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Sorry Eric but that is not ( in my opinion ) a smart thing. To me it is a way of making money by selling things to gullible people.

Imagine a bus driver whose route takes him past his home address two or three times a day, heating comes on two or three times a day when the house is empty.

Far too many unforeseen problems, or seen but ignored by the people selling technology for profit.

I agree with @bernardgreen there is very little adjustment one can make to so called smart devices, with geofencing one should be able to select the size of the fence, but your not given the option.

With a modern house the insulation is rather good, we don't all live in 509 year old thatched cottages, and turning off the heating and the rate of cooling is rather slow, mothers detached house built 1954 with now double glazing and cavity wall insulation plus loft insulation, if heating was turned off at 10 pm, then even on the coldest day at 7 am it never dropped from 20°C to 16°C in that time, and at 18°C when the TRV was set to 20°C the anti-hysteresis software came in to stop over shooting, so I had to cheat and set the TRV to 22°C at 7 am and then 20°C at 8 am or it would be 11 am before room at 20°C.

OK I know Drayton Wiser TRV heads do work this out, and so will reheat a room fast, but not convinced simple timed changes in temperature are not better than geofencing.

ericmark said:

we don't all live in 509 year old thatched cottages

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510, missed the birthday, but to be serious, the thick stone walls do act as thermal stores and slow the rate of change of temperature. Cool in summer and warm in winter,

The big problem with both mothers house and mine is windows which allow the sun to heat rooms, you can get outside sensors to turn down the water temperature as it gets warmer outside, but not to counter the effects of the sun, mother bay windows even in winter could heat the living room to 30°C even in the winter, so wanted the TRV to react fast, wax heads were too slow, using electronic heads the room still over heated, but only to 25°C once using electronic heads.

ericmark said:

windows which allow the sun to heat rooms,

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Blinds or curtains.

flameport said:

Blinds or curtains.

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The French type of blind on the outside would clearly work, not so sure inside the room, seems special glass which allows heat to travel in one direction not the other so even white curtains will not reflect the heat, although it would keep the heat to window area. But try getting a mother with alzheimer's disease to let you have curtains closed in the day.

Getting a little off subject, but when house built metal frames single glazed windows with holes in bottom of frames to allow condensate to drain outside did not have a problem with sun over heating room in winter, only as we start using k glass and double glazing plus cavity wall insulation and block up the draft up chimney with a gas fire does the sun start to cause a problem.

The same exists with light switches, with tungsten lights and simple on/off switches there was no problem not having a neutral at the light switch, the problems only arrived as we started to use electronic switches and electronic light bulbs. It would be nice if we had a standard, if all light bulbs were designed to pass 1 mA without flashing then manufacturers could design dimmer switches and other electronic switches knowing how much power could be passed, but there are no such rules, and since most countries use the switch back box as the junction box and not the ceiling rose as used in this country we are unlikely to get any standard leakage allowance.

In this house most of the light switches don't have a neutral, one exception is the 4 gang light switch in the hall, which has two neutrals, one for entrance level lights and one for upper floor lights, and yes they got them mixed up, so until I fitted all RCBO consumer unit, we had two borrowed neutrals, so not convinced having a neutral at the switch is a good idea! I would guess reason for neutral at switch was two of the switches worked outside lights.