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

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st...@theharperfamily.net

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Oct 23, 2008, 4:27:28 AM10/23/08
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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

meow...@care2.com

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Oct 23, 2008, 4:32:08 AM10/23/08
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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

d...@gglz.com

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Oct 23, 2008, 5:34:10 AM10/23/08
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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

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Oct 23, 2008, 7:06:39 AM10/23/08
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st...@theharperfamily.net wrote:

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

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

> 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

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.

> 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......

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)

> 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.

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)


--
Cheers,

John.

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Matty F

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Oct 24, 2008, 2:42:58 AM10/24/08
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On Oct 23, 10:34 pm, "d...@gglz.com" <d...@gglz.com> wrote:
> 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.

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.

st...@theharperfamily.net

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Oct 27, 2008, 8:38:13 AM10/27/08
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Many thanks to all who answered. I implemented the suggestion by meow2
and it works really well!

Regards

Steve H

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