Help wiring PIR into lighting circuit

In wiring in the PIR are you planning on doing away with the lightswitch or are you hope to be able to overide the PIR with the switch if required.

 

The black sleeved red is your switch wire in the ceiling rose. Disconnect this from the ceiling rose. Then take a 3-core and E from the ceiling rose to the PIR by connecting the switch wire in the rose on to a connector block to brown on the 3-core and this will go to the L in on the PIR. Mark the grey in the 3-core with blue tape (or sleeve it with blue sleeving) and connect this to the black neutral terminals in the ceiling rose and to the neutral in on the PIR. This will transfer control of the light switch to the PIR. Then take the black on the 3-core and mark it with brown tape (or sleeve it brown) and connect this back in to the ceiling rose switch live terminal. Connect the other end on to the PIR switched live.

Wired like this, switching the hall light switch on will activate the PIR and the hall light will switch on when there is movement past it. It will switch off after a pre-set time. If you turn the hall light switch off the light won't come on.

 

These PIRs have a manual override. If wired the way JP suggests, switching the light switch quickly twice will cause the lights to latch on.

I would suggest using two two core cables, rather than a three core, and removing the factory link to allow independent relay control. One two cor supplying perm live and neutral to the detector, the other two core in series with your current switch job. Very similar to how JP explained.