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New way to wire lighting circuits
David Sakho
10 Posts
Question
Hello,

Does anyone know anything about a new rule to wire lighting circuits so that they have a live, neutral and earth running the full length of the circuit? I heard something about this last year but cannot pinpoint it in the 18th Edition Regs.

Apparently, a light now has to be wired so that the neutral running to the switch is USED as a neutral, and not as a switched live.

Anyone else heard of this?

Thanks,

David
17 Replies
Sparkingchip
3370 Posts
I’ll pass on that one for the moment 🤨
aligarjon
58 Posts
A lot of sparks take the mains through the switch these days rather than 3 plate at the light fitting when possible, myself included.  It makes it a lot easier to fit some of these light fittings that can be quite tight.  Also easier to then just loop through down lights.  It isn't a regulation just another way of doing things.   A switched live is just that, just because the colour of the core is that of a neutral conductor doesn't make it a neutral.  It is sleeved at both ends to indicate it's function.    There are, or certainly used to be twin and earthed cable available with 2 red or brown cores.


Gary
AJJewsbury
2013 Posts
I think someone's over-interpreted 559.5.1.208 - which says consideration should be given to providing a N at switches - to allow for power for electronic controls (the old fashioned approach of controls parasitically pinching power between L and SL doesn't work so well with low energy lamps).

   - Andy.
mapj1
2663 Posts
Indeed, not a requirement, just permitted.
559.5.1.208 Consideration shall be given to the provision of the neutral conductor, at each switch position, to
facilitate the installation of electronic switching devices.


Actually it's always been permitted,  as there are some layouts of building where to do anything else makes no sense.
If you like you could have a socket at the light switch, albeit one of limited current capacity.

There are some pretty daft sections in that bit of the regs. actually.

Try this for a giggle.
...the connecting device shall be:
(i) terminals according to BS EN 60998, or
(ii) a device for connecting a Juminaire (DCL) plug according to BS EN 61995, or
(iii) an installation coupler according to BS EN 61535, or
(iv) supporting coupler (LSC) plug according to BS 6972 or BS 700 I, or
(v) a male connector (plug) of a plug-in lighting distribution unit according to BS 5733, or
(vi) another suitable and appropriate connecting device.


Well it strikes me that if you have (iv) the other lines could safely be deleted,
unless they are suggesting they are somehow  permitted but 'unsuitable'


 
broadgage
400 Posts
IIRC, in the USA there is a proposal to require a neutral at the light switch, for future flexibility for electronic controls.
In the UK, as others have already said it is permitted but not required.

There is also a lot of VERY ill informed demand for neutrals at the light switch to "improve safety" Circuits with the two conductors well seperated can give rise to electromagnetic fields, that may be harmful to health.
With a conventional 2 wire drop to a light switch, the "go" and "return" conductors are immediatly adjacenr and no significant electromagnetic field results. That however does not stop the mumsnet types from demanding neutral at every switch to "prevent rays that might harm a baby"
David Sakho
10 Posts
Thanks for the answers everyone, I'll look up that part of the Regs book.

A follow on question, what do you do with a conventional light switch in this scenario? Do you use single core browns for the common and SL and terminate the neutral in a connector or Wago, or is there a new type of light switch available with separate terminals for the L,N and E?
mapj1
2663 Posts
It makes most sense when lighting circuit is fed from below - i.e. the upstairs lights and loft lights. Then LNE arrive from below the switch and leave to the light above. Otherwise it can be wired rather as a 2 way light switch, wired in 3core+E, with 2 cores L and SL as before and the other one N.
I'm not aware of any switch with a parking contact for N, though I am aware of cases of it being stuffed in the back contact of a 2 way switch, which in effect shorts out the light when it is off.  This is not wise, and confuses the unwary - the smallest wagos or a slice of chock block are your friends.
Don't forget blue sleeving is available as well as brown.
There is a modest EMC advantage to the fed from below method (not for health, but in terms of RF pick up or emission, as in the looped out method we have in effect got an antenna like a folded dipole on the L and not the N, so any differential mode L-N signals are now radiated.) With well filtered equipment this is not necessary.
Blencathra
86 Posts
Hager switches have a loop terminal for neutrals
Arran Cameron
432 Posts
What do you think of the idea of powering ceiling lights from the ring main via a FCU in each room? That way the neutral conductor is available at every light switch.
mapj1
2663 Posts
The switched fuse spur as a light switch is quite common for situations on the end of a long feed, like sheds / outbuildings, or places where the lighting circuit does not need to go, such as cellars, understairs cupboards or for the wall lights in modest conservatories.
Electrically it is fine, after all combined lights and power is the continental way, and they seem to have no  issues with it.
The slight weakness is that if you do manage to trip the sockets off, you lose those lights as well, so maybe not ideal for living areas or situations like a kitchen, where being plunged into dark while holding something sharp or hot would be an issue.
Still no worse than a small flat with one RCD for everything, and there are lots of those.
regards Mike.
Simon Barker
769 Posts
Arran Cameron:
What do you think of the idea of powering ceiling lights from the ring main via a FCU in each room? That way the neutral conductor is available at every light switch.

The obvious problem is that one faulty electrical appliance will noy only take out all the sockets on that ring, but take out all the lights at the same time.  That's not great at night.

AJJewsbury
2013 Posts
The obvious problem is that one faulty electrical appliance will noy only take out all the sockets on that ring, but take out all the lights at the same time. That's not great at night.
That's one of the unfortunate side-effects of the current fashion for MCBs and RCDs at the CU. Under the original design 13A fuses discriminated very nicely with 30A CU fuses, which in turn discriminated very nicely with 60A supplier's fuses. Other than gross overload the only way you could blow the 30A fuses was a fault on the ring itself. Appliance faults could only disconnect the faulty appliance.
   - Andy.
ebee
860 Posts
" The obvious problem is that one faulty electrical appliance will noy only take out all the sockets on that ring, but take out all the lights at the same time.  That's not great at night. "

Like said . Us front enders have the same problem (or rather do not have much of a problem in practice for more than 25 years)
aligarjon
58 Posts
Using a switched spur also might look a bit odd when you require more than one switch. 3 spurs in a line would be daft.  I suppose you could use a grid then only one fuse with multiple switches.  Still not a good design though losing all lights and sockets in one hit.


Gary
Sparkingchip
3370 Posts
NArran Cameron:
What do you think of the idea of powering ceiling lights from the ring main via a FCU in each room? That way the neutral conductor is available at every light switch.


Why not combined 16 amp socket and lighting radials without SFCU as light switches?

broadgage
400 Posts
In general, for main living areas in a home, I consider it better practice to utilise seperate circuits for power and lighting as is tradditional. I dont like the risk of total darkness due to a single fault.

I see no harm in connecting a light to a power circuit via a fused connection unit in sheds, garages, and lofts used only for storage.
lyledunn
418 Posts
If AFDDs are mandated, I could see lots of fellas being tempted to combine circuits such as lightning via a spur from a ring. That way only one AFDD is required instead of two!

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