Home electrics - peculiar landing light behaviour.

Hello,
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.
Reply to
David Paste
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.
Reply to
Harry Bloomfield, Esq.
No, U/S circuit off, all U/S room light switches off.
How would one identify and fix this, or is it a job for a professional?
Thanks.
Reply to
David Paste
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).
Cheers
Dave R
Reply to
David
On Sat, 19 Sep 2020 07:23:35 -0700 (PDT)
What does it do when it is not operating correctly?
Reply to
Pink
Its DIYable if you take it step by step...
Here is an overview of some of the common ways lighting circuits are wired:
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and here are the common ways of doing 2 way switching (i.e. one lamp switched from two (or more) locations):
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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?
Reply to
John Rumm
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 earth.
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.
Reply to
newshound
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.
Reply to
Dave Liquorice
professional?
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.
Reply to
Dave Liquorice
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.
Reply to
Fi
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?
Reply to
Roger Hayter

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