I am not an electrician.
Upstairs landing light is part of the downstairs lighting circuit. The landing light only operates (correctly) when the upstairs lighting circuit is OFF at the fuse board. When the upstairs lighting circuit is on, the landing light does not operate. All other lights operate normally.
Anyone have any ideas?
Thanks in advance,
David Paste wrote on 19/09/2020 :
..and presumably when an upstairs light has been left turned on?
Neutral for landing light, is connected to what would be the live of
the upstairs lighting circuit. The neutral needs to be directed to a
neutral of the downstair lighting cuircuit.
It seems obvious from what you describe that supplying power to the
upstairs light circuit prevents this light from working.
If you feel up to it you should trace the wires from downstairs to
upstairs and to the light fitting to make sure that there are no wires
from the upstairs lighting circuit connected at any place.
You would need some kind of MultiMeter to check for current and continuity.
However possibly better to leave this to an electrician unless you already
have a pretty clear idea of how house wiring works (or should work).
Its DIYable if you take it step by step...
Here is an overview of some of the common ways lighting circuits are wired:
and here are the common ways of doing 2 way switching (i.e. one lamp
switched from two (or more) locations):
Now, one of the common bodges you will see done is to borrow a neutral
connection from the "other" circuit. (this is dangerous practice at best!)
Now in this case I am guessing that is how your circuit was wired, but
with the added complication that your "borrowed neutral" has actually
been connected to a live on the upstairs circuit and not a neutral.
So when the upstairs circuit is off at the fuse board, the live is left
floating, but will still be connected indirectly to neutral via any
lamps or other loads currently "on" on that circuit (and pulling a fuse
or turning off a MCB does not usually disconnect the neutral).
When did this problem first start?
Have there been any recent changes to the electrical system?
Depends really on your competence and confidence (in that order). It
might not be fixable just by swapping wires at the switches, you might
be missing one wire running between upstairs and downstairs (a plausible
DIY error that a professional wouldn't make). The fault may have been
introduced by a wiring modification.
Or it could be that the wires are there, they are just connected
slightly wrong (perhaps after someone replaced a broken switch).
"Proper" two way wiring will use cable with three insulated wires plus
an earth (used to be red, yellow, and blue but I think that has
changed). Or it can be done more wastefully with two sets of "twin plus
Easier to diagnose if you only have single switches top and bottom. A
bit more complicated if there are two or even three gang switches.
If it is just one switch at each end, unscrew the switches each end
(with the power off) and pull them out for a look. That may show if you
have "3+E" cable. If your consumer unit has a residual current trip on
the lighting circuit it's difficult to electrocute yourself even with
the power on. You will need a multimeter (or volt stick or, at a pinch,
neon screwdriver) to poke around in live circuitry to work out what is
going on. Plenty of diagrams on the web. Label the wires and draw a
diagram of what you have.
But remember you can't sue on the basis of advice from the net.
If it was a swap yes, but I think we are really just talking about a
wire being connnected to live when it should be connected to neutral
(or the opposite).
The light doesn't work because it has the same voltage either side of
it, be that voltage be effectively nothing (neutral both sides) or
230 V (live both sides).
When it works the current is finding another way to flow to complete
the ciruit. It might not be flowing in the direction you think it
ought to be as well.
To be fair until the advent of RCDs everywhere the "borowed neutral"
for two way switching wasn't a problem. We have one here, though
using the term "professional" for who ever did the wiring in that
part of the building might be pushing it a bit.
On Sat, 19 Sep 2020 07:23:35 -0700 (PDT)
My guess is that the light has 2 lives (instead of live and neutral) and
only gets a path to neutral (through a shaver socket, or something of
the sort) when the upstairs circuit is not powered.
Are you saying the landing light won't go on when the upstairs circuit is
powered, or that it won't turn off when the upstairs circuit is powered? When
the landing light comes on, is it normal brightness for the size of bulb used?
Is it an incandescent bulb or fluorescent or LED?