Hi all,
I changed the light in the hallway, outside my bedroom, with an energy
saver.
Can't remember the exact make, but it's the folded tube type, as
opposed to the 'bulb' shaped ones.

Anyway, the weird thing is, even when the light switch is OFF, the lamp
gives a small dim flash every 10 seconds or so. I never noticed till I
walked under it in the darkness last night.

I've removed the bulb and held it in my hand, and nothing, so it must
be getting some 'energy' from the wiring, but how can this be even when
it's switched off????

Any suggestions? All I can think of is that the wiring must be wrong,
and the live is permanent and the neutral is being switched. Could this
cause the flashes?

-Confused, Glasgow.

On 21 Feb 2005 14:46:28 -0800, "kmillar" wrote:

Hi all,
I changed the light in the hallway, outside my bedroom, with an energy
saver.
Can't remember the exact make, but it's the folded tube type, as
opposed to the 'bulb' shaped ones.

Anyway, the weird thing is, even when the light switch is OFF, the lamp
gives a small dim flash every 10 seconds or so. I never noticed till I
walked under it in the darkness last night.

I've removed the bulb and held it in my hand, and nothing, so it must
be getting some 'energy' from the wiring, but how can this be even when
it's switched off????

Any suggestions? All I can think of is that the wiring must be wrong,
and the live is permanent and the neutral is being switched. Could this
cause the flashes?

-Confused, Glasgow.

They will do this if fed a small leakage current. For example if switched by an electronic time
switch, or a switch with a neon across it (sometimes used to help find them in the dark).

If neutral is switched, then capacitive leakage might also just do it.

"kmillar" wrote in message
oups.com...
Hi all,
I changed the light in the hallway, outside my bedroom, with an energy
saver.
Can't remember the exact make, but it's the folded tube type, as
opposed to the 'bulb' shaped ones.

Anyway, the weird thing is, even when the light switch is OFF, the lamp
gives a small dim flash every 10 seconds or so. I never noticed till I
walked under it in the darkness last night.

I've removed the bulb and held it in my hand, and nothing, so it must
be getting some 'energy' from the wiring, but how can this be even when
it's switched off????

Any suggestions? All I can think of is that the wiring must be wrong,
and the live is permanent and the neutral is being switched. Could this
cause the flashes?

-Confused, Glasgow.


I'm sure someone else reported this effect in this newsgroup a couple of
weeks ago. I believe the answer was that the live wire was inducing a small
current in the neutral wire. I don't think it's anything to worry about.
Someone who knows more may explain it better.
Nodge

Mike Harrison wrote:

They will do this if fed a small leakage current. For example if switched by an electronic time
switch, or a switch with a neon across it (sometimes used to help find them in the dark).

If neutral is switched, then capacitive leakage might also just do it.

There's still capacitive leakage when the live is switched (the
capacitance between the wires going to the switch and back). It seems
to be enough to give this flashing effect with some lamps.

This is an FAQ. A compact fluorescent lamp has a bridge rectifier
across the mains followed by a reservoir capacitor. These parts provide
a DC supply to an electronic oscillator circuit (an inverter) that
provides the high-frequency current for the lamp tube. What's happening
is this: when the lamp is off there's no load presented to the
oscillator and very little load on the rectifier. Any small leakage
current in the wiring - quite normal, not necessarily a sign of a fault
- charges up the reservoir capacitor, via the rectifier. The voltage
across the capacitor increases steadily until it's high enough to start
the inverter and power the lamp, which lights. This lamp load now
rapidly discharges the capacitor, the inverter stops and the light goes
out. The brief flash is all over in a millisecond or so and the whole
cycle starts again.

Try different makes of lamp. Some don't do it, probably because they've
go internal bleed resistors. Also I guess it's much more likely to
happen with the cold-start types (the sort that come on 'instantly').
The warm-start ones won't ever get through their pre-heat phase on
leakage current alone.

--
Andy

In article , Andy Wade
writes
Mike Harrison wrote:

They will do this if fed a small leakage current. For example if switched by an
electronic time
switch, or a switch with a neon across it (sometimes used to help find them in
the dark).

If neutral is switched, then capacitive leakage might also just do it.

Try different makes of lamp. Some don't do it, probably because they've
go internal bleed resistors. Also I guess it's much more likely to
happen with the cold-start types (the sort that come on 'instantly').
The warm-start ones won't ever get through their pre-heat phase on
leakage current alone.

The cheap alternative (LT 20p) would be to add a bleed resistor across the
lamp wires in the ceiling rose yourself, a 1Mohm one should do the job but
you'll need one of the right voltage rating eg. Mapin's 0.6W range won't do
but their 2W or 'high voltage' ranges will. Alternatively two 470k from just
about any leaded range connected in series across the lamp will have
sufficient voltage rating.

Easiest connection would prob be to twist with the flex side wiring before
screwing down the terms and bare leads on the resistor(s) should be
sleeved.

--
fred

fred wrote:

The cheap alternative (LT 20p) would be to add a bleed resistor across the
lamp wires in the ceiling rose yourself,

That went through my mind too, but I think that introducing such
non-standard things into the fixed wiring is not a good idea. It would
need to be recorded on a note attached to the electrical installation
certificate or last periodic inspection report (if any) otherwise it
could confuse the hell out of anyone trying to do an insulation
resistance test.

--
Andy

In article , Andy Wade
writes
fred wrote:

The cheap alternative (LT 20p) would be to add a bleed resistor across the
lamp wires in the ceiling rose yourself,

That went through my mind too, but I think that introducing such
non-standard things into the fixed wiring is not a good idea. It would
need to be recorded on a note attached to the electrical installation
certificate or last periodic inspection report (if any) otherwise it
could confuse the hell out of anyone trying to do an insulation
resistance test.

Fair comment about the note but I'm not sure if I understand your point
about the insulation test. The bleed would be directly across the load
where a next-to-no-ohm incandescent would normally be. . . . . Just
thinking about it again though, is a proper insulation test carried out with
all loads disconnected (ie bulbs removed) and switches on/off as required,
that would make sense for a comprehensive test, presumably with fixed
loads such as water heaters and cookers being a special case?
--
fred

On Tue, 22 Feb 2005 11:03:15 GMT, fred strung together
this:

Fair comment about the note but I'm not sure if I understand your point
about the insulation test. The bleed would be directly across the load
where a next-to-no-ohm incandescent would normally be. . . . .

But you can remove a bulb, as you should when testing, but the
resistor would still be across the live cables.

Just
thinking about it again though, is a proper insulation test carried out with
all loads disconnected (ie bulbs removed) and switches on/off as required,
that would make sense for a comprehensive test, presumably with fixed
loads such as water heaters and cookers being a special case?

Fixed loads should have an isolator so they can be turned off for
testing.
--

SJW
Please reply to group or use 'usenet' in email subject

Thanks everyone for the excellent replies.
I must admit, I rather jumped the gun at assuming a wiring fault,
because since I moved into this house a month ago, I've found some real
horrors going on behind sockets etc.

e.g Light switch in kitchen was tempramental, turned out that the wires
behind the switch were not screwed down, just poked loosely into the
holes. A socket I removed in the front room, had soo much insulation
stripped (about 2 inches!) that there were live bare wires just folded
up into the pattress. None of the earth conductors are sheathed, and
none of the 'black' wires used as switched lives in the lighting
circuit are sheathed. (I thought it was law that any conductors used as
live should be appropraitely coloured, or sheathed?)

Anyway, thanks again everyone.
-K

In article .com,
kmillar writes
Thanks everyone for the excellent replies.
I must admit, I rather jumped the gun at assuming a wiring fault,
because since I moved into this house a month ago, I've found some real
horrors going on behind sockets etc.

e.g Light switch in kitchen was tempramental, turned out that the wires
behind the switch were not screwed down, just poked loosely into the
holes.
This seems to be quite common, I think the screws work or vibrate loose
over time. I found two sockets in our kitchen like this.

A socket I removed in the front room, had soo much insulation
stripped (about 2 inches!) that there were live bare wires just folded
up into the pattress. None of the earth conductors are sheathed,

OOerr, that doesn't sound nice

and
none of the 'black' wires used as switched lives in the lighting
circuit are sheathed. (I thought it was law that any conductors used as
live should be appropraitely coloured, or sheathed?)
I have been inside a lot of light switches in various houses and have
yet to see one with red sheathing on the switched live.
--
Tim Mitchell

On Tue, 22 Feb 2005 14:33:49 +0000, Tim Mitchell wrote:

In article .com,
kmillar writes
Thanks everyone for the excellent replies.
I must admit, I rather jumped the gun at assuming a wiring fault,
because since I moved into this house a month ago, I've found some real
horrors going on behind sockets etc.

e.g Light switch in kitchen was tempramental, turned out that the wires
behind the switch were not screwed down, just poked loosely into the
holes.
This seems to be quite common, I think the screws work or vibrate loose
over time. I found two sockets in our kitchen like this.

A socket I removed in the front room, had soo much insulation
stripped (about 2 inches!) that there were live bare wires just folded
up into the pattress. None of the earth conductors are sheathed,

OOerr, that doesn't sound nice

and
none of the 'black' wires used as switched lives in the lighting
circuit are sheathed. (I thought it was law that any conductors used as
live should be appropraitely coloured, or sheathed?)
I have been inside a lot of light switches in various houses and have
yet to see one with red sheathing on the switched live.

Can't see any point in red-sleeving at the switch end as it's usually obvious. Would be handy in
the rose or junction box however.

Yes I have never seen it in the 'real world' either, but was instructed
it was necessary when I did some elimentary electrical training at
college a few years back.

I was studying a degree in Electronic Engineering (B-Eng) and they
actually PAID us to go to college during the summer break to study
things like welding, domestic electrics, industrial electrics, tool
making, plumbing and vehicle crash repairs. Apparently they wanted us
to get a feel for the other industies which we would be working in. Was
well worth sacrificsing summer break for!