Switch with neon indicator

[Kit Jackson]

I've got some lights in the loft with the switch in the passageway
below. It's not unknown for the loft lights to be left on all night or
even all weekend if I don't notice the switch.

I'd like to replace the switch with one that has a neon indicator. The
problem is that the lights have been wired with a loop-in circuit so that
the power runs from ceiling rose to ceiling rose and only the switched
live is taken down to the light switch. The neon switch I've got seems
to require the neutral to be present as the neon is soldered between the
live and neutral on the load side of the switch.

Is there any way to wire this so the a neon switch would work without the
need to drop another cable from the rose to the switch? Or can you get
neon switches that will work without the need for the neutral to be
present?

Kit Jackson

[Andy Burns]

Kit Jackson wrote:

> Is there any way to wire this so the a neon switch would work without the
> need to drop another cable from the rose to the switch? Or can you get
> neon switches that will work without the need for the neutral to be
> present?

In the past I've had touch dimmers that had a neon which worked without
a neutral, back in the days of incandescent lamps they probably were
able to pull enough current from neutral through the lamp, probably not
these days with CFLs. Or just maybe they treated the earth as a
"neutral" a bit naughty as it would tip an RCD a few mA more towards
tripping.

[Adrian Caspersz]

On 20/10/16 22:54, Kit Jackson wrote:
> I've got some lights in the loft with the switch in the passageway
> below. It's not unknown for the loft lights to be left on all night or
> even all weekend if I don't notice the switch.
>

Drill a small hole in the loft door?


--
Adrian C

[tabb...@gmail.com]

The switch has live & switched live, so the neon would be on when lights off, wrong way round.

OP needs a neutral, assuming not going to connect neon to earth. Earth return isn't allowed, though with a [suitable] stack of resistors the risk would be pretty much zero.

Or maybe mount a neon into the ceiling, its wiring then being in the loft.


NT

[Brian Gaff]

Not really or reliably, Is there an earth present?
Sounds like a bit of dodgy wiring to me.

Brian

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[Brian Gaff]

If you are goint to do the latter, you could probably use an led and some
little circuit to bleed of just enough th run the little led, but its a
bodge.

Brian


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<tabb...@gmail.com> wrote in message
news:5eb9c564-fe7e-4250...@googlegroups.com...

[Muddymike]

On 20/10/2016 22:54, Kit Jackson wrote:
> I've got some lights in the loft with the switch in the passageway
> below. It's not unknown for the loft lights to be left on all night or
> even all weekend if I don't notice the switch.

As an aside this reminds me of the hotel owners that went into their
attic to thaw frozen pipes with an electric heater only to find one
already there and switched on...

From when the pipes froze 8 years before!

Mike

[Martin Brown]

On 21/10/2016 08:25, Brian Gaff wrote:
> Not really or reliably, Is there an earth present?
> Sounds like a bit of dodgy wiring to me.
>
> Brian

If you don't mind the lit neon indicating the loft lights are *NOT* on
then you can wire the neon indicator in parallel with the switch.

Otherwise you need a local neutral from somewhere.
Deliberately adding earth leakage current isn't a good idea.

--
Regards,
Martin Brown

[Syd Rumpo]

On 20/10/2016 22:54, Kit Jackson wrote:

Feed the live through a current transformer primary with a pair of
inverse parallel LEDs on the secondary. Winding details are left to the
student.

Cheers
--
Syd

[Syd Rumpo]

Like this, perhaps...

https://www.youtube.com/watch?v=JxpERETpqfI

He's used just one LED, which isn't great, LEDs shouldn't have reverse
current through them, but the clip-on core idea is good.

Cheers
--
Syd

[Michael Chare]

On 20/10/2016 22:54, Kit Jackson wrote:

> neon switches that will work without the need for the neutral to be be
> present?
>
> Kit Jackson
>

If the switch cable goes straight up from the switch to the loft it
might not be that difficult to replace it with a 3 core and earth cable.
You could see if the cable can move a little


--
Michael Chare

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[The Natural Philosopher]

and he can detect an electric fire, but not necessarily a lightbulb.

Fora fixed installation I see no reason why a very small mains
transformer used backwards - i.e. with the low voltage winding in series
with the switched load - would not work as well.


> Cheers


--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

[Dave W]

"Syd Rumpo" <use...@nononono.co.uk> wrote in message
news:nucjlc$n0m$1...@dont-email.me...

That's a great idea. It could be done without a transformer. Assuming one
60W incandescent bulb in the loft, it takes 250mA. Six 1 amp diodes wired as
three back-to-back pairs all in series with the switched live, would drop
about 1.5V and dissipate 0.6W overall per bulb. Wire a LED in series with a
470 ohm resistor across the diode array, to give about 2mA into the LED. If
there are other bulbs in the loft, use LED types to keep the overall current
down. Of course house all the components in an insulated box.
--
Dave W

[Syd Rumpo]

I like that. Maybe use 4 diodes, one in inverse parallel with a string
of three in series to further reduce dissipation. Or a single 1.8V
Zener, if you can find one.


Cheers
--
Syd

[Andy Burns]

tabb...@gmail.com wrote:

> The switch has live & switched live, so the neon would be on when lights off, wrong way round.

Yes, it's been a while since those dimmers were removed, the neon was of
course on when the lamp was off and vice-versa, so an aid to finding the
switch, rather than an indicator that it hand been left on by accident

> Earth return isn't allowed

I did say "naughty"

[harry]

Buy yourself a light switch illuminator.
Requires no neutral.
But may need an incandescent lamp.
http://www.builderdepot.co.uk/mk-neon-plateswitch-locator.html?gclid=CjwKEAjw-abABRDquOTJi8qdojwSJABt1S1OpclFeWxfBl5J75fKNHz5w2f04p9o4cOKkvMlMpetbRoC8nrw_wcB

They are on when the light is off however.

[newshound]

Lateral thinking! I like it!

[harry]

[Mike Clarke]

On 21/10/2016 09:09, Martin Brown wrote:
> Otherwise you need a local neutral from somewhere.

Providing that "somewhere" is on the same circuit. Borrowed neutrals can
cause problems.

--
Mike Clarke

[Dave W]

"Syd Rumpo" <use...@nononono.co.uk> wrote in message

news:nucoc1$6n3$1...@dont-email.me...

Yes you are right. You might get away with only two diodes in the forward
direction and one in reverse, and a lower value of resistor.

I've now had an even better idea. Put a 12V 5W festoon car bulb in series
with the live circuit. Such a bulb normally takes about half an amp in the
car, so 250mA would generate only 6V across it, leaving the rest of the
mains voltage for the 60W bulb, and might glow nicely especially if behind a
red filter.
--
Dave W

[Johnny B Good]

Tungsten filament lamps have a very high positive temperature
coefficient of resistance. Typically, the hot resistance is an order of
magnitude greater than its cold resistance for ordinary tungsten
filaments running in an evacuated envelope such as that festoon lamp.

Halving the current doesn't simply drop the voltage to half, more likely
to one quarter or less. Indeed, using that lamp as envisaged, you may not
even be able to see it glow at all without peering very closely at the
naked lamp whilst shading it from any bright room lighting.

The use of a LED lamp with a fullwave bridge rectifier plus 4 or 5
silicon diodes in series across the DC output and a series current
limiting resistor for the LED itself wired across the resulting voltage
clipped rectifier output is a far better idea if you don't mind losing 4
or 5 volts from the lamp supply. However, the best version of this
"Current Flow Detector" wired in series with the lamp switched live (on ac
supplies) is the already proposed use of a current transformer.

If you're going to go to the trouble of using the CT option, choose the
turns (or current) ratio carefully so that the indicator LED will glow
just as brightly with a 10W LED lamp as it will with that 60W
incandescent lamp you mentioned.

Assuming a high quality 10W LED (the 810 Lm equivalent of the American
60W incandescent 120v 750 hour rated lamp, aka the 75W 230v 1000 hour UK/
European equivalent), you'd be looking at a line current of 42mA at unity
power factor. That's your worst case condition. In all probability,
you'll fit a cheap as chips (fvsvo 'cheap') lamp using a simple
"capacitive dropper" ballast circuit with a PF figure the wrong side of
the 50% mark resulting in a current more in the region of 80 to 100mA.

If we assume the "worst case scenario" from the point of view of
guaranteeing a minimum lumens output from our indicator LED then we only
need to decide on how much current will prove sufficient to allow the
indicator LED to meet this minimum illumination level. Depending on the
desired brightness and efficiency of the LED, you're probably looking at
an indicator LED current in the region of 1 to 10mA[1].

If you assume the upper figure the CT ratio would need to be a minimum
of 4:1 which quite frankly, seems rather a low ratio for a CT. A few
years back, I modded the mains sockets fed from my UPS protected supply
to provide a "Power Present" indicator lamp. I used vintage (at least two
decades old at the time) 3mm dia red LEDS wired in anti-parallel with a
cheap 1A silicon diode with a small capacitor and an inrush limiting
resistor in series with the LED wired across the Live and neutral.

ISTR using a 47nF cap with a 2K2 half watt resistor for the capacitive
volt dropper. When I tentatively checked out the impedance of a 100nF cap
by way of a 'sanity check' to jog my memory just now, I was looking at a
reactance value at 50Hz of just 32K ohm (just over 7mA's worth if true)
so I'm pretty certain I'd have used the more space saving value of 47 or
possibly even 33 nF.

Bearing in mind that the LED only sees half of the current cycles in
this simple circuit I'm looking at an average current of just 1.75mA (or
possibly even just over 1mA with a 33nF cap). These vintage red LEDs
provide a more than bright enough indication so I rather suspect a mere
one mA will more than suffice using modern higher efficiency indicator
LEDs with a fullwave rectifier. If we assume a 1mA current in the
secondary of the CT, this allows the use of a 40:1 CT, a more typical
turns ratio value for an off the shelf CT imo. :-)

The original circuit (F/W rect with 4 or 5 voltage clamping diodes (or
3v3 zenner diode) feeding a LED via a current limiting resistor) is
simply wired across the low current secondary of the CT and the primary
wired in series with the live feed to the lamp. Instead of losing 5 volts
or so, you'll only lose 125mV across the CT's high current primary.
Furthermore, the rectifier and voltage clamping diodes need only handle
one fortieth of the lamp current which is a bonus when it comes to coping
with short circuit fault currents.

You might even be able to make your own CT using a ferrite ring with 20
to 40 turns of fine (28 SWG?) enamelled copper wire wound onto the ring
which can then be threaded onto the switched live conductor, neatly
avoiding having to insert an extra connector into the circuit. :-)

If you have a suitable ferrite ring and the yard or two of fine
enamelled copper wire to hand, you can build a test circuit and test with
a suitable lamp holder wired to a 13A plug (I'm assuming the indicator
LED and other components won't be a problem for you to source).

There's just one final note: You may find this CT based current
indicator possibly a little too sensitive to fully extinguish when the
light is switched off. If this turns out to be the case, just wire
another resistor (10K?) across the rectifier output pins to divert this
'nuisance current' around the LED part of the circuit.

[1] That was a ball park guess which, on reflection (that memory jogging
exercise re the average current in those power present indicator LEDS)
was rather on the high side even for vintage LED indicator lamps, let
alone the more efficient indicator LEDs available today. If you don't
mind the painful brightness of blue LEDs you can reckon on only needing a
tenth of the current required by a red LED.

--
Johnny B Good

[John Rumm]

On 20/10/2016 22:54, Kit Jackson wrote:

There is no obvious way of doing it with a neon, but you could do it
with an LED.

If you took say 4 silicon rectifier diodes, and arranged them so that
you have three of the silicon diodes in series with the switched live,
then the fourth in parallel with them but reversed in direction, you
should have a bi-directional current path through the switch and the
lamp(s). Now wire LED with a series current limiting resistor across the
three silicon diodes, and there should be sufficient voltage drop across
the silicon diodes to forward bias the LED and cause it to light.

(The LED will be in effect running from a half wave rectified supply, so
you may see some flicker on it. This could be more pronounced if the
load you are switching is a low energy lamp rather than an incandescent
You could add a smoothing cap if that is a problem)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[DerbyBorn]

>

Why not just add an extra light - as a downlight in the ceiling below -
that is on the same circuit as the loft lights. It will be an easy prompt
to turn them off.

[Dave W]

"Johnny B Good" <johnny...@invalid.ntlworld.com> wrote in message
news:XbyOz.323370$BF.1...@fx42.am4...

Yes I know. That's why I said "might glow". If it's not visible, try using
more than 60W in the loft (we don't know what the OP has), or a lower
wattage 12V bulb.

I've just tried a 6V 5W festoon bulb on a controlled current supply, taking
0.8A.
When reduced to 0.4A the voltage across it was only 1V. So my post should
have said 2V not 6V. However my result was a visible glow similar to a neon.

<lecture snipped>

--
Dave W

[Dave Plowman (News)]

In article <nucg4m$ck6$1...@dont-email.me>,

Brian Gaff <bri...@blueyonder.co.uk> wrote:
> If you are goint to do the latter, you could probably use an led and
> some little circuit to bleed of just enough th run the little led, but
> its a bodge.

LEDs generally need about 10mA to be decently bright. Not sure I'd want
that deliberately flowing on an RCD protected circuit.

--
*You are validating my inherent mistrust of strangers

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[alan_m]

On 20/10/2016 22:54, Kit Jackson wrote:

>

> Is there any way to wire this so the a neon switch would work without the
> need to drop another cable from the rose to the switch? Or can you get
> neon switches that will work without the need for the neutral to be
> present?
>
> Kit Jackson
>

Construct a current transformer with a clip on ferrite 'suppression'
core with a led and diode across the output.



--
mailto: news {at} admac {dot] myzen {dot} co {dot} uk

[Bob Minchin]

alan_m wrote:
> On 20/10/2016 22:54, Kit Jackson wrote:
>
>>
>> Is there any way to wire this so the a neon switch would work without the
>> need to drop another cable from the rose to the switch? Or can you get
>> neon switches that will work without the need for the neutral to be
>> present?
>>
>> Kit Jackson
>>
>
>
> Construct a current transformer with a clip on ferrite 'suppression'
> core with a led and diode across the output.
>
>
>

Have you actually tried that? I've not either but I would suspect the
ferrite designed for suppression would not have much response at 50Hz.
Happy to be educated otherwise if it works.

[tabb...@gmail.com]

On Saturday, 22 October 2016 13:48:54 UTC+1, Dave Plowman (News) wrote:
> In article <nucg4m$ck6$1...@dont-email.me>,
> Brian Gaff <bri...@blueyonder.co.uk> wrote:

> > If you are goint to do the latter, you could probably use an led and
> > some little circuit to bleed of just enough th run the little led, but
> > its a bodge.
>
> LEDs generally need about 10mA to be decently bright. Not sure I'd want
> that deliberately flowing on an RCD protected circuit.

1970s LEDs maybe.


NT

[ARW]

On 20 Oct 2016 21:54:05 GMT, Kit Jackson <m...@nowhere.com> wrote:

>I've got some lights in the loft with the switch in the passageway
>below. It's not unknown for the loft lights to be left on all night or
>even all weekend if I don't notice the switch.
>
>I'd like to replace the switch with one that has a neon indicator. The
>problem is that the lights have been wired with a loop-in circuit so that
>the power runs from ceiling rose to ceiling rose and only the switched
>live is taken down to the light switch. The neon switch I've got seems
>to require the neutral to be present as the neon is soldered between the
>live and neutral on the load side of the switch.
>

>Is there any way to wire this so the a neon switch would work without the
>need to drop another cable from the rose to the switch? Or can you get
>neon switches that will work without the need for the neutral to be
>present?
>
>Kit Jackson

Why not just put the switch in the loft?

[bruce]

On 2016-10-22 15:21:13 +0000, ARW said:

> On 20 Oct 2016 21:54:05 GMT, Kit Jackson <m...@nowhere.com> wrote:
>>
>> Is there any way to wire this so the a neon switch would work without the
>> need to drop another cable from the rose to the switch? Or can you get
>> neon switches that will work without the need for the neutral to be
>> present?
>>
>> Kit Jackson
>
>
> Why not just put the switch in the loft?

Wire it between live and earth if the rcd, if any, will take it.

[Dave Plowman (News)]

In article <1675c7ee-ea4b-4e62...@googlegroups.com>,

I was assuming it needed to be clearly visible in bright light.

--
*Lawyers believe a man is innocent until proven broke.

[tabb...@gmail.com]

On Sunday, 23 October 2016 00:34:15 UTC+1, Dave Plowman (News) wrote:
> In article <1675c7ee-ea4b-4e62...@googlegroups.com>,

> <tabbypurr> wrote:
> > On Saturday, 22 October 2016 13:48:54 UTC+1, Dave Plowman (News) wrote:
> > > In article <nucg4m$ck6$1...@dont-email.me>,
> > > Brian Gaff <bri...@blueyonder.co.uk> wrote:
>
> > > > If you are goint to do the latter, you could probably use an led and
> > > > some little circuit to bleed of just enough th run the little led,
> > > > but its a bodge.
> > >
> > > LEDs generally need about 10mA to be decently bright. Not sure I'd want
> > > that deliberately flowing on an RCD protected circuit.
>
> > 1970s LEDs maybe.
>
>
> I was assuming it needed to be clearly visible in bright light.

Modern LEDs are IME visible indoors in daylight on very little current. Even mid 1980s LEDs were normally visible on 10mA indoors.


NT

[DerbyBorn]

>

Don't risk leaving behind a bodge if you die! It will spoil your
reputation. (I still worry about the neon I bridged to earth in a room
thermostat that didn't have a neutral)

[alan_m]

On 23/10/2016 03:01, tabb...@gmail.com wrote:

> Modern LEDs are IME visible indoors in daylight on very little current. Even mid 1980s LEDs were normally visible on 10mA indoors.

I have recently fitted a couple of 5mm green LEDs to an outdoor wall
plaque and running at 500uA from a battery they are visible outdoors on
a sunny day. At night they are way too bright and this week I may reduce
the current.

[Dave Plowman (News)]

In article <e74c1v...@mid.individual.net>,

alan_m <ju...@admac.myzen.co.uk> wrote:
> On 23/10/2016 03:01, tabb...@gmail.com wrote:

> > Modern LEDs are IME visible indoors in daylight on very little
> > current. Even mid 1980s LEDs were normally visible on 10mA indoors.

> I have recently fitted a couple of 5mm green LEDs to an outdoor wall
> plaque and running at 500uA from a battery they are visible outdoors on
> a sunny day. At night they are way too bright and this week I may reduce
> the current.

OK. I've not got any near that sort of efficiency. Never really been that
worried about efficiency for signal types anyway.

--
*Marriage changes passion - suddenly you're in bed with a relative*

[whisky-dave]

On Sunday, 23 October 2016 18:58:25 UTC+1, alan_m wrote:
> On 23/10/2016 03:01, tabb...@gmail.com wrote:
>
> > Modern LEDs are IME visible indoors in daylight on very little current. Even mid 1980s LEDs were normally visible on 10mA indoors.
>
> I have recently fitted a couple of 5mm green LEDs to an outdoor wall
> plaque and running at 500uA from a battery they are visible outdoors on
> a sunny day. At night they are way too bright and this week I may reduce
> the current.
>

Any link for these LEDs the lowset current I've seen is 2ma and they aren't all that bright.

[Martin Brown]

Most of the current generation of LEDs are bright enough to see that the
die is lit up in daylight with about 10uA flowing. Allowing that much
leakage will allow you to find an LED torch in the pitch dark.



Once dark adapted you can see by the light it emits on 10uA current.

If you want something visible in full sun then you will need a bit more
current but modern LEDs are plenty bright enough to do the job.

I prefer the 3M glotorch dayglo plastic which can manage to store enough
sunlight to illuminate a room for adapted night vision.

--
Regards,
Martin Brown

[whisky-dave]

On Tuesday, 25 October 2016 22:04:40 UTC+1, Martin Brown wrote:
> On 25/10/2016 09:45, whisky-dave wrote:
> > On Sunday, 23 October 2016 18:58:25 UTC+1, alan_m wrote:
> >> On 23/10/2016 03:01, tabb...@gmail.com wrote:
> >>
> >>> Modern LEDs are IME visible indoors in daylight on very little current. Even mid 1980s LEDs were normally visible on 10mA indoors.
> >>
> >> I have recently fitted a couple of 5mm green LEDs to an outdoor wall
> >> plaque and running at 500uA from a battery they are visible outdoors on
> >> a sunny day. At night they are way too bright and this week I may reduce
> >> the current.
> >
> > Any link for these LEDs the lowset current I've seen is 2ma and they aren't all that bright.
>
> Most of the current generation of LEDs are bright enough to see that the
> die is lit up in daylight with about 10uA flowing. Allowing that much
> leakage will allow you to find an LED torch in the pitch dark.
>
>
>
> Once dark adapted you can see by the light it emits on 10uA current.

could you at least link to this magic LED's becaus ethe only refernce I could find wass one pulsed at a much higher current than 10uA closer to 100uA and higher and with a very narrow viewing angle.

>
> If you want something visible in full sun then you will need a bit more
> current but modern LEDs are plenty bright enough to do the job.

at a couple of ma yes but nit at uA.

>
> I prefer the 3M glotorch dayglo plastic which can manage to store enough
> sunlight to illuminate a room for adapted night vision.

Not much use as indicators though are they.

[Dave Plowman (News)]

In article <c7ca175d-7b23-4071...@googlegroups.com>,

whisky-dave <whisk...@gmail.com> wrote:
> > Most of the current generation of LEDs are bright enough to see that
> > the die is lit up in daylight with about 10uA flowing. Allowing that
> > much leakage will allow you to find an LED torch in the pitch dark.
> >
> >
> >
> > Once dark adapted you can see by the light it emits on 10uA current.

> could you at least link to this magic LED's becaus ethe only refernce I
> could find wass one pulsed at a much higher current than 10uA closer to
> 100uA and higher and with a very narrow viewing angle.

Yup. I'd be interested too. I'd be using a large diffused type as a signal
which can be seen from a wide range of postions, and want one which was
clearly visible in any likely lighting condition. Not much point in having
a warning light if you have to go right up to the switch to see it.

--
*If at first you don't succeed, then skydiving definitely isn't for you *