Outside light to an old house...help!

[fatmantrev]

Hi folks,
Just joined this forum today whilst searching for an answer to my latest DIY dilema..hope you can help me
I live in a 1930's house and have gradually been replacing old for new, but my latest venture has me stuck.
I'm trying to fit an outside light, which naturally needs 3 cables...neutral, live and earth.
Not a problem in that I have 3 cables from the old set-up you'd think, except that they are, what appears to be anyway, 1 x black (neutral?) and 2 x red (both live?), with not an earth in sight!
Obviously there is a way to get around this, but given I'm fitting a halogen PIR lamp with "expensive" bulbs, I don't want to experiment 20 times (and blow as many bulbs) before I get it right.
Anyone know what I need to do. Any help much appreciated.
Thanks
Trev

 

[plugwash]

umm right

you didn't perhaps consider that the wiring is probablly in need of replacement anyway before you started adding stuff willy nilly?

i think frankly you probablly need to rewire

 

[fatmantrev]

Yeah, a fair proportion of it was replaced by a qualified sparky, I'm just "modernising" some of the bits not done though.
Any "constructive" help much appreciated.
FMT

 

[plugwash]

that in itself sounds dodgy

i don't know of many sparkys who would wan't to do a partial rewire leaving old crap like that in place

there is definately somthing odd going on there and without actually being there with test equipment its near impossible to figure out

 

[Lectrician]

The earth isnt sleeved red is it????

When you say 3 cables(you mean cores), do they all come out from the same cable sheath?? (ie ONE cable)

 

[fatmantrev]

There are, what I would call, 3 main cables coming out through the wall.
All are about 6mm diameter, and a dirty grey / black in colour.
Where the ends have been cut back and exposed you can see the wires inside.
2 are sheathed in red, 1 in black, hence my assumption I have 2 lives and a neutral...not an earth in sight.
Are cables are totally independant, not part of a larger sheathing further back.
FMT

 

[Lectrician]

Sounds like a diyer gone mad....i think you are talking about single core double insulated.

The earth may well me one of the reds.....BUT IT DEFFINANTLY SHOULDNT BE.

 

[Darkness]

Is it possible to trace the the cables back to a source which you may able to tell from that what the extra 'red' cable is for?

Some old buildings I've seen, they often used one of the cables like the live one for the earth especially if using overhead cables to install power to outbuildings. In doing so, they continued to use this cable as earth.

Stupid but old times.

If you could follow the cables then great.

 

[fatmantrev]

It's strange because the wiring at the switch end is quite modern.
Plastic sheathed, holding 3 wires, red, blue and yellow.
How the hell turns into what it does outside only 4 feet away is anyone's guess, there must be a real concoction in the cavity I guess.
How do I find out which of the red's is live and which is the earth?
FMT

 

[securespark]

How were these wires connected to the old light?

 

[fatmantrev]

If only I knew.
The connectors were all rusted over and I couldn't get to see any of them, so I just isolated from the mains and cut through.
Even when the light was off I still couldn't get at anything. The 3 wires definitely ran to 3 different connectors, none were doubled up.

 

[plugwash]

in any case its highly dodgy

also do you have two way switching of that light and if so what is the wiring like at the other switch