DIY Doctor

outisde light using existing switched live connection

Postby graemewood » Sun Nov 23, 2008 11:03 am

I am trying to replace an existing light with a new light, but the cabling is different and somewhat confusing.

I have the following at present:-

Connector block 1
Two black wires from wall (B1 and B2) terminted together using connector block

Connector block 2
One green wire from wall (G1) terminated at connector block

Connector block 3
1st red wire from wall (R1) connected to blue wire of existing light
One green wire from wall (G2) terminated at connector block
2nd red wire from wall (R2) connected to white wire of light

The new light is a pir light and has the Blue, Green and Brown connections.

Any help would be appreciated.
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Postby sparx » Sun Nov 23, 2008 8:48 pm

From your description it seems the original wiring is connected incorrectly!
It would be normal for the 2 red wires to be connected together but not to the light.
This is 'live in' linked to live to switch.
the 'green' earths should be together and join with the earth green/yel. from light fitting.
The remaining 2 blacks are Neutral in, which goes to Blue of light, & sw.line back (which should have red sleeve or tape on) which connects to Brown of light.
You will need in some way to identify which 'Black' is really the 'red' sw. line.
With power off [using say a multimeter on ohms continuity scale] test from sw. to light to see which black is the sw.line, this may need a length of spare wire to reach end to end.
As you are to connect a PIR light leave switch 'ON' except to reset after any power glitches which can cause such lights to stay on permanently
The existing set up would appear to switch the Neutral not live, which will work BUT is potentially dangerous as if switched off to change a lamp the light would go off but lampholder would still be live to earth!!
If unsure or unable to test system seek qualified help as lighting circuit outside may well not have RCD protection and is easily capable of giving lethal shock!
regards SPARX
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