Confused 120v & 240v Wiring - Please Help

Hi, I'm looking for some help with a wiring problem I have encountered in the house we've just bought. I should add that I'm a reasonably competent electrician, yet this one has me puzzled!!
We have a lounge ceiling light with rose, with a standard 1 way switch attached. When I turn on the switch, the light works! Inside the rose the connections appear to standard. LNE in, LNE Loop through, the switch cable which has been wired with Twin & E so that the switch box is earthed, and obviously a LNE to the actual light fitting.
At the lIve terminal in the switch there is another L going off to god only knows where, this live comes from a separate Twin and Earth cable of which the N has just been cut short, and the E goes to the earthing point.
NOW for the fun bit.
We have an outside light which is switched by a fused switch next to the front door. This has a Twin and Earth coming in, with a Twin and Earth going to the fixture- no loop through, this seems to just be a spur off the dowstairs lighting ring.
When the LOUNGE SWITCH is ON, there is 0v going to the OUTDOOR LIGHT SWITCH. When the LOUNGE SWITCH is OFF and the OUTDOOR SWITCH is OFF there is 240v at the OUTDOOR LIGHT SWITCH.
When the LOUNGE SWITCH is OFF and the OUTDOOR SWITCH is ON, there is 120v at the OUTDOOR SWITCH, and 120v at the LOUNGE LIGHT & SWITCH!!!!! i.e both bulbs are at half power, even though the lounge switch is OFF
Please help. I've given up trying to draw parallel and serial circuits because I can't work out how the 1 way switch in the lounge can in effect turn off or on the power in the Outdoor switch?
Many thanks for any suggestions.
James
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It sounds as though the outside light has been tapped off the live side of the lounge circuit but not been issued with a neutral connection and is more than likely running to earth through the filament of the lamp in the outside light. The 120 volts is being back fed through either the earth or the live.
Try taking the lamp out of the outside light fitting and doing your voltage test again. If it's dead, then the outside light is definitely wired wrong.
If the outside light fitting is wired from the lighting circuit, then it won't really need a fused switch because it is already being protected by the lighting breaker in the consumer unit (fuse box).
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BigWallop wrote:
snip

I've actually seen this done more than once, and the reason behind it being that it is a reminder that the outside light is still on when the lounge light is turned off to go to bed!!
I kid not, and yes the people involved were misers ;)
Lee
--
To reply use lee.blaver and ntlworld.com


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Thank you for help so far guys, it's dark here now, so I'll have another look at the job next weekend. Will post results. I found out where that spare live from the lounge switch goes though! To the inside hall light!! Obvious really !!!
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