On 26 Jun, 00:58, Jamie
t wrote:
Ron(UK) wrote:
Eeyore wrote:

"Ron(UK)" wrote:

If the neutral wire isn't properly grounded enough voltage can be
induced by or leak from other 'live' circuits, maybe enough to cause the
fluorescent fittings to randomly flicker.

Ron, when the switch is off, there is no circuit. The neutral potential
literally doesn't matter.

Graham

It`s a two way switch, there`s plenty of potential for leakage paths.
You can easily get 100v on the neutral if it`s floating above earth
potential.

Ron(UK)

Hmm.
2 way, 3 way , 4 way and any number of ways you want! why would that
matter?, the neutral should not be part of the switching circuit.


I have not examined this particular circuit in detail yet. When I
came to the house, I was surprised to find three switches for this
landing light. I was used to two and knew how they worked but three
was new to me. I checked how it could be done and found this. The
neutral is connected directly to one of the socket terminals. Each of
the switches has two inputs and two outputs. The two inputs are
always connected to the two outputs but when the switch is moved the
connections are swapped. The live goes to one of the inputs to the
first switch. The two outputs from this switch go to the two inputs
of the next and so on through as many switches as you like (three in
my case). Finally one output from the last switch goes to the other
socket terminal. So, it is always possible for any switch to change
the state of the lamp. This will mean that the two possible live
wires run together for a considerable distance, more than the length
of the landing due to detours to the switches but the inductance
theory still surprises me (I am not saying impossible my knowledge of
electromagnetism is too old and rusty to say that). Animal damage or
some other cable damage sounds quite possible, a leakage between these
two lines would not blow a fuse but just allow a small current to
flow. Checking this cable is going to be quite unpleasant since the
loft is very small. The last time that I was up there, a few years
ago, to install aerial cable, the lighting cables appeared to be OK.

I will start by checking out all the switches since this is a
relatively easy job.

I can also use a multimeter and one of those neon screwdrivers to
perform some more tests. Sticking the probes of the multimeter into
the light socket sounds a little scary. This is a UK lamp socket
which may be unfamiliar to US readers and some others. The bulb does
not screw in it is a bayonet mount. You push the bulb in and turn and
a couple or prongs catch the mount and hold the bulb. The contacts
are two sprung pins which press onto contacts at the bottom of the
bulb. The collar is metal. To UK readers and others who know the
system: is the collar connected to anything? If my multimeter probe
touches a contact and the collar, is something nasty going to happen?
Obviously if both probes touch their contacts and the collar,
something nasty may happen.

--
Seán Ó Leathlóbhair