Discuss Non-standard lighting cabling: single neutral plus multiple switch lines - is it OK? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Mark42

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I’m upgrading some lighting circuits to a programmable ‘Futronix’ system (similar to Lutron). The 16 x 5A channels Futronix panel is fed from a single-phase 40A 30mA RCBO.

It’s in a listed timber-frame building with very difficult cable runs.

I need to transfer the switching of four lighting circuits in one difficult room from local control to the Futronix panel 20m away. Total load of these four circuits does not exceed 1kW, 4A.

What I need to know is whether it’s OK to use a non-standard wiring technique as follows:

Option 1: Use 4No. 1.0mm T&E cables - standard method, clearly acceptable but ugly and bulky to run surface.

Option 2: Use 1No. 3C&E 1.0mm plus 1No. T&E, employing, from the five sheathed cores available, four for the switched lines and one for neutral. Plus the two unsheathed grounds.
Or maybe use two 3C&E, and double up the neutral. Still a bit bulky though.

Option 3: Use 2 No. lengths of four-core flex in 0.5mm: Four switch lines, two neutrals and two grounds.

Option three is by far the most aesthetically acceptable, and I’m minded to go with that one. But it feels wrong.

Both ends of the exposed switch line cores will be fully covered with brown shrink-fit.

Note that these are switch lines, not separate final circuits - the switching occurs at the Futronix panel. It’s only electrically unusual in that the ‘switch’ is so far away.

BTW, I can’t find any 6- or 7-core flex in thin section. SY would be great, but is way too big.

Any ideas?

Many thanks, Mark
 
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Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

What about a 6 or 7 core YY flex.

YY Control Cable BS6500
 
Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

Brilliant!

CSE Distributors 7 Core YY PVC / PVC Control Cable

7 cores of 0.75, quite thin at only 7.3mm OD so aesthetically OK for surface installation, and cheap at 60p a metre from CSE.

Great stuff for running multiple lighting circuits to various individual rooms from modern remote control panels like Futronix or Lutron.

Thanks. Job done.

It still feels odd using flex for fixed wiring though :)
 
Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

Although I am a bit of a fan of using flex myself (have used plenty in my house, including multiple cores as you are doing), I'm pretty sure there is a reg somewhere that states the allowable length of a flex when used for fixed wiring, although I couldnt find it anywhere when I looked.
Obviously you'd have to be carefull about your R1+R2 values, and volts drop, if you are concerned about such things:D
 
Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

Although I am a bit of a fan of using flex myself (have used plenty in my house, including multiple cores as you are doing), I'm pretty sure there is a reg somewhere that states the allowable length of a flex when used for fixed wiring, although I couldnt find it anywhere when I looked.
Obviously you'd have to be carefull about your R1+R2 values, and volts drop, if you are concerned about such things:D
Yes, I'm very concerned about such things :) This is my own house, and it's made of wood. So hot cables would get my full attention! Thanks for the reminder anyway.

The loads are trivial, and I have enough cores to double up the neutral or protective conductor if necessary. I'll probably change the supplied 6A C breakers in the Futronix panel for 1A B's as well. Might trip when lamps blow, but that's no big deal. With soft-start digital dimming, lamps last for ages anyway.

BTW, I can't see why there would be any electrical reason why flex should be treated differently from solid core in any regulation. Multi-core is as bunched as it comes, so there may be different volt drop factors, but surely no length restriction per se.
 
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Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

is paralleling .75's allowed

not allowed here anyhow

you can drop the breaker size alright


not trying to be a wiseass but are the 1amp B's for incandescent-they wouldn't be suitable

-suppose maybe with softstart you might get away-except for bulbs blowing
 
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Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

is paralleling .75's allowed ...
Oh dear, I didn't think about that! If not, why not?

...not trying to be a wiseass but are the 1amp B's for incandescent-they wouldn't be suitable
-suppose maybe with softstart you might get away-except for bulbs blowing
Nothing wrong with being a wiseass - I appreciate the input!
Yes, for180W tungsten circuits (3 x 60W lamps). 1 sec soft start (but can adjust this in software up to two hours - a really useful feature that :))

I'm just really uncomfortable with using thin multicore flex. Whatever the theory says, it simply feels wrong. Hence my unthinking choice as I was writing the post. Not ordered yet. Perhaps 2A or 3A is better?

I'm happy if a blown lamp trips the breaker. On a programmed system there's no way of easily turning off just one circuit whilst leaving the others on (depending of course on the scenes programmed), so a tripped breaker gives the opportunity to replace a lamp immediately, whilst being able to see what you're doing, and with only one walk out to the DB. (Yes, I know you have to find which lamp has gone but don't be a wiseass :))
 
Re: Non-standard lighting cabling: single neutral plus multiple switch lines - is it

Oh dear, I didn't think about that! If not, why not?


Nothing wrong with being a wiseass - I appreciate the input!
Yes, for180W tungsten circuits (3 x 60W lamps). 1 sec soft start (but can adjust this in software up to two hours - a really useful feature that :))

I'm just really uncomfortable with using thin multicore flex. Whatever the theory says, it simply feels wrong. Hence my unthinking choice as I was writing the post. Not ordered yet. Perhaps 2A or 3A is better?

I'm happy if a blown lamp trips the breaker. On a programmed system there's no way of easily turning off just one circuit whilst leaving the others on (depending of course on the scenes programmed), so a tripped breaker gives the opportunity to replace a lamp immediately, whilst being able to see what you're doing, and with only one walk out to the DB. (Yes, I know you have to find which lamp has gone but don't be a wiseass :))

here 'paralleling' is used for distribution circuits and 10sq minimum csa
(ignoring ring ccts)

alarm guys double up SELV wires for VD-but i wouldn't mind that

i would prob be thinking of 1sq minimum for fixed wiring


have you looked at doing this without re-wiring using x10 or similar-afraid i don't know much
 
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