A difficult to describe lighting question regarding feeding a light via two circuits.

[steve]

I have tried looking thru the posting history and the UK diy faq for this point, but as I am finding it hard to describe it in the correct terms, I have been unable to find an appropriate phrase to search on.

If possible, I want the following arrangement:

4 external lights for a patio, fed from a single switch. 1 of these lights also fed on a separate circuit via a PIR. If the first circuit is on, all 4 lights are lit, if the first circuit is off, the single light is fed via the PIR when it activates. They are physicallt two separate circuits, the switch for the 4 external lights circuit is conveniently by the patio doors, the switch for the PIR circuit is in the basement (it controls other lights too).

At the moment, I have isolated the PIR controlled light from the other

3 patio lights so they are working separately but it is annoying when outside with the patio lights on that the light in one corner of the patio switches on and off depending on people moving about.

Can I achieve what I want or is it just against all regulations etc?

If I can, how might I do this? I can't just feed the single light from both circuits as that sounds dangerous to me (they are on separate lighting circuits at the consumer unit too). I need some sort of isolating relay/switch arrangement such that if the first circuit is active, the PIR is isolated and likewise, if the PIR is active, 3 of the lights and the feed are isolated. Then copious amounts of labelling to explain that the light can be fed from two sources....the more I think about it the less likely I feel it is I can do this without falling foul of the regualtions......

I might add that there is no chance to change any of the wiring except at the PIR/single light as the construction work is complete.

Thanks in advance for any help!

Steve H

[meow2222]

Lights 1-3 are on switch 1 on circuit 1. Light 4 is on the PIR on circuit 2. Switched side of circuit one powers a relay's coil. The relay's contacts short out the switching device in the PIR, thus switching on light 4 when 1-3 are also on. All you need is a 240v relay.

You should also include a switch for light 4 that disconnects power to it, regardless of what the PIR or relay does.

Yes, there are other ways to do it.

NT

[dom]

Some PIR lights have a feature, that you switch them on, then switch them off briefly, and immediately switch them on again - to go into a "permanently on" state.

If yours hasn't, it might be easiest to change the light (or if separate) the sensor.

[John Rumm]

There are a number of ways of doing what you want...

Indeed, don't do this - in effect you would end up joining the two circuits in all likelihood. Ignoring the confusion this might cause, you could also end up with two MCBs/fuses etc feeding power to it, leaving the cables inadequately protected.

It sounds like a simple solution is using a double poll switch. Use one poll switch the three pario lights, and use the other to switch the live to the switched live of the PIR circuit (most PIRs have a terminal available so that you can get at the switched live - you can either use this to switch other lights, or in fact drive it to switch the light even when the PIR itself is not calling for light)

You will need one additional cable between the switch position and PIR position...

(I usually run feeds to PIRs and their associated lights using three core and earth cable, so that you have the flexibility of using or overriding the switched live from multiple locations)

[Matty F]

The manual for my PIR light says that it has this feature, but it usually doesn't work when I want it to. In addition if there is a very short power cut, then it decides to turn the lights on indefinitely, perhaps when I'm on holiday, thus wasting lots of power and burning out the bulbs prematurely. Also when the PIR has been switched off for hours, when I switch it on it insists on turning the lights on for a minute, attracting the attention of anyone casing the neighbourhood.

I would love to buy a PIR that just turned the lights on when there is movement, and did absolutely nothing else. I do not want those stupid extra features.

[steve]

Many thanks to all who answered. I implemented the suggestion by meow2 and it works really well!

Regards

Steve H