Only a porch light

[pasty-man]

Long time since last post but this still remains the place for great advice & a smattering of part p!

Could someone please guide me ....I wish to put a pir activated light ,100w tungsten, in the porch.
1st question - Is it acceptable to connect onto existing mcb for downstairs lighting circuit, 'in parallel'. Ie have 2 radial circuits protected by the same mcb (B6). The max load on existing circuit is only a few hundred watts so no problem here, its just much more practical & tidier to wire from cu than existing lighting circuit & theres no room for additional mcb.
2nd question - As this will be a pir activated light do I have to provide a means of isolation as well ie a plate switch?
3rd question - If a switch is needed & wiring from cu ok then can I do a slightly non standard switch connection (as this would be a 1 light circuit)and take the neutral crimp connected through the backbox, with the switched live?Just means 1 cable really.
last q - Can anyone comment on the general functionality of a pir when approached almost straight on in close proximity as would be the case here if I use a light with integrated pir. Imagine outer porch door slide open, 2 steps forward to locked door, light just to right of this door, fumble with keys, light comes on!?


I look forward to comments.

 

[Adam_151]

1st question - Is it acceptable to connect onto existing mcb for downstairs lighting circuit, 'in parallel'. Ie have 2 radial circuits protected by the same mcb (B6). The max load on existing circuit is only a few hundred watts so no problem here, its just much more practical & tidier to wire from cu than existing lighting circuit & theres no room for additional mcb.

Perfectly acceptable to do this, but it'll create one radial circuit branched at the cu, not two radial circuits, IMHO, If the light is going on the outside of the porch, as opposed to in it, disconnection time is 0.4 don't think there is too much difficulty meeting this with a B6 though

2nd question - As this will be a pir activated light do I have to provide a means of isolation as well ie a plate switch?

Be best to (you flick the power on an off a few times to override the PIR on most lights), i'd probably use a 20A DP switch

3rd question - If a switch is needed & wiring from cu ok then can I do a slightly non standard switch connection (as this would be a 1 light circuit)and take the neutral crimp connected through the backbox, with the switched live?Just means 1 cable really.

If you were using a standard light switch ou could do that, I'd probably use a DP switch as above, which means there would be no need for any crimping either..

last q - Can anyone comment on the general functionality of a pir when approached almost straight on in close proximity as would be the case here if I use a light with integrated pir. Imagine outer porch door slide open, 2 steps forward to locked door, light just to right of this door, fumble with keys, light comes on!?

Sorry no I can't, but most of them are adjustable to an extent
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[1974stephen]

Even though the sensitivity is significantly decreased when approaching any PIR straight on , in such a short distance of a few feet, this shouldn't actually effect this too much. I would suggest this won't cause you a problem. If it were coming up a 8m drive for example, then I wouldn't advise it, otherwise seems fine.

 

[pasty-man]

Cracking advice gents(?) My sincere thanks for such a prompt response!!

 

[Steve]

please make sure the sensitivity is adjusted so that passing cats 20 metres away dont turn it on. One of my neighbours has just had a PIR light fitted at the front (their house is 5 metres from a lamppost) and it comes on for 3 seconds at a time every time something moves on the street. I sleep at the front of our house, with the curtains slightly open, and this is what i get all night now, i can see the light on my wall going on and off.