Ring circuit for LIGHTING

Installing a lighting ring, it may be easier to install using Double pole switching formed as a ring, both Live and Neutral at the switches.

We do big supermarkets and there lighting is often 4mm and sometimes a pain getting 2 into a multi grid switch bank, often in 25mm pipe, sometimes think they could have been 2.5 rings instead.
I don't see why having it as a ring makes that any more possible/easy. What am I missing?

Kind Regards, John
At a quess, similar to what the Dno use to supply premises, they can remove links and temporary feed from one end, whilst they work on a dodgy section
 
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At a quess, similar to what the Dno use to supply premises, they can remove links and temporary feed from one end, whilst they work on a dodgy section
Fair enough - that might be an explanation, but obviously not relevant/appropriate in a domestic environment (in which I seriously doubt that a lighting ring is ever justified).

Kind Regards, John
 
Installing a lighting ring, it may be easier to install using Double pole switching formed as a ring, both Live and Neutral at the switches.

We do big supermarkets and there lighting is often 4mm and sometimes a pain getting 2 into a multi grid switch bank, often in 25mm pipe, sometimes think they could have been 2.5 rings instead.

At a quess, similar to what the Dno use to supply premises, they can remove links and temporary feed from one end, whilst they work on a dodgy section
Out of academic interest, what size protective device do you tend to use with 4mm2 lighting wiring?
 
Out of academic interest, what size protective device do you tend to use with 4mm2 lighting wiring?
I was wondering that. Depending on the installation method, a 32A OPD might be, and a 25A one almost certainly would be, OK in terms of such a cable - but then (if it were not for other regs), the likes of eric would then presumably get worried about the 6A, or at most usually 10A, 'rating' of accessories and fittings commonly used on lighting circuits.

However, the regs trump that to some extent because, if I recall correctly, for some reason they limit a 'lighting circuit' (however defined!) to a 16A OPD).
[ I think I might be tempted to add a socket or two and then say that it was "not a lighting circuit", even if it 'happened' to be supplying some lights as well as sockets (just as very many sockets circuits do) :) ].

Mind you, even a 16A 'lighting circuit' would leave eric with concerns!

Kind Regards, John
 
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I suspect 20 amp grid switches and the like could be used, and I know a lot of commercial and industrial light fittings, typically fluorescents, have a fuse built into the main connector block, apart from that I don't really know.
 
We do big supermarkets and there lighting is often 4mm and sometimes a pain getting 2 into a multi grid switch bank, often in 25mm pipe, sometimes think they could have been 2.5 rings instead.

I do think that if the job ends up with stuffing 4mm into a lighting grid switch then maybe a better design was possible, quite often when folk are stuffing lighting circuits through the design software its done as if the load is all at the furthest point, also not always relevant but if the cable is run signficiantly below its current carrying capacity, you can gain a bit on volr drop there because its never at the assumed operating temperature. Zs issues are often less of an issue in steel framed buildings if metallic wiring systems are used (although some finger in the air is necessary at design stage). Sometimes better to switch the bigger lighting cirucits via contactors and if switching via contactors, nothing to stop it being a three phase lighting circuit with the lighting couplers being on each phase in turn as you go down the row.
 
Out of academic interest, what size protective device do you tend to use with 4mm2 lighting wiring?
Most were installed in the late 70's, when the stores were built, nowadays its only replacing the damaged switches really, there still only 6 or 10 amp circuits, so i assume the 4mm was used to reduce the volt drop.
Those days it was flourescent with magnetic chokes and i seem to remember some struggled to strike with reduced voltage
 
I suspect 20 amp grid switches and the like could be used,...
Yes, that's very possible. However, in contrast to what many people seem to believe, I see no reason why (if such were allowed - which it's not, per BS7671 for a 'lighting circuit') they would not be OK on a circuit with a 32A OPD. In relation to the 'rating' of the switch, all that really matter is the current lakelet to go through (and potentially 'broken' by) its contacts 'in normal use' does not exceed the 'rating' of the switch, and it's extremely unlikely that a grid switch would be used in a manner that such would be the case.

Having said that, as recently said by someone, getting two 4mm² conductors into each terminal of a grid switch (paricularly within a group of grid switches) might be a struggle, so maybe such switches are less likely to be used in a circuit wired with 4mm² cable.
... and I know a lot of commercial and industrial light fittings, typically fluorescents, have a fuse built into the main connector block, apart from that I don't really know.
I can't speak from experience, but that sounds very credible. However, it doesn't alter the fact that, as far as I am aware ****, BS7671 does not allow a 'lighting circuit' (in any environment) to have an OPD greater than 16A, in which case there would obviously be no concerns about 20A switches.

Edit: I've just looked, and the 16A limit only applied to "Lighting circuits incorporating B15, B22, E14, E27 or E40 lampholders" - so probably doesn't usually apply to the commercial/industrial installations we're talking about.

Kind Regards, John
 
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I do think that if the job ends up with stuffing 4mm into a lighting grid switch then maybe a better design was possible, quite often when folk are stuffing lighting circuits through the design software its done as if the load is all at the furthest point, also not always relevant but if the cable is run signficiantly below its current carrying capacity, you can gain a bit on volr drop there because its never at the assumed operating temperature. Zs issues are often less of an issue in steel framed buildings if metallic wiring systems are used (although some finger in the air is necessary at design stage). Sometimes better to switch the bigger lighting cirucits via contactors and if switching via contactors, nothing to stop it being a three phase lighting circuit with the lighting couplers being on each phase in turn as you go down the row.
These switches were originally installed by others back in the day, as you say the newer stores are all canalis track,pir's contacters and plug in Klik boxes nowadays
 
Yes, that's very possible. However, in contrast to what many people seem to believe, I see no reason why (if such were allowed - which it's not, per BS7671 for a 'lighting circuit') they would not be OK on a circuit with a 32A OPD. In relation to the 'rating' of the switch, all that really matter is the current lakelet to go through (and potentially 'broken' by) its contacts 'in normal use' does not exceed the 'rating' of the switch, and it's extremely unlikely that a grid switch would be used in a manner that such would be the case.

Having said that, as recently said by someone, getting two 4mm² conductors into each terminal of a grid switch (paricularly within a group of grid switches) might be a struggle, so maybe such switches are less likely to be used in a circuit wired with 4mm² cable.
I can't speak from experience, but that sounds very credible. However, it doesn't alter the fact that, as far as I am aware ****, BS7671 does not allow a 'lighting circuit' (in any environment) to have an OPD greater than 16A, in which case there would obviously be no concerns about 20A switches.

Edit: I've just looked, and the 16A limit only applied to "Lighting circuits incorporating B15, B22, E14, E27 or E40 lampholders" - so probably doesn't usually apply to the commercial/industrial installations we're talking about.

Kind Regards, John

We see a lot of these used in stores often on a 20 amp radial switched via a contacter, the makers even provide made up leads which I think are 1mm cable, when they first came out i was advised they should only be used with lights that had internal fusing, but nowadays fused fittings seem rare.
I dont see nothing in the makers info stating these boxes cannot be fused even higher , thus the fitting and the plug/flex fused at that same rating.


shopping
 
I've just looked, and the 16A limit only applied to "Lighting circuits incorporating B15, B22, E14, E27 or E40 lampholders" - so probably doesn't usually apply to the commercial/industrial installations we're talking about.
You beat me to it!
 
I've come across a number of lighting rings, especially commercial and I've installed 4mm² 16A rings in a tunnel purely to get Zs down. it was a right royal PITA getting 2 4mm² into the Fluo fittings as we had to fit an extra 30A choc bloc and a smaller link to the original connectors. We wanted to replace the original but the quality controller wouldn't accept modified fittings.

The last domestic lighting ring circuit I found was this one:
upload_2021-11-14_2-17-17.png

In this thread: https://www.diynot.com/diy/threads/a-real-moan-tonight.552183/
 

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