2.5mm² for a lighting circuit? (And why not in a ring??)

[edenbridge]

Excuse me for being a bit dense, but there's no reason why I can't use a 2.5mm² T&E for my lighting circuits, is there?

It's just that I don't want to crack open a new reel of 1.5mm² when I have a load of 2.5mm² leftover. I can take the unused 1.5mm² back to B&Q, but they might be a bit annoyed if I try it on with a long offcut of mains cable!

I presume the use of 1.5mm² is something to do with the size of cable you can fit into the dainty little terminals in light fittings and switches?

I'll be using a pair of 6A MCBs ready for my lighting spurs, of course, and a job-lot of 20A junction boxes in the loft to make the connections between these 2.5mm² 'busbars' and the light fittings (I also have a load of 1.0mm² I can use for short spurs to the light fittings and switches.)

And BTW, what exactly is the problem of having a ring circuit for your lights??

 

[holmslaw]

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[electronicsuk]

Don't use 2.5mmsq, you'll struggle to get it into light fittings and switches, it might lead to the circuit being incorrectly identified at some point in the future, it's bad practice and you might even damage the fittings/switches trying to push such a mass of cable back into the wall.

A 100m reel of 1.5mmsq isn't exactly going to break the bank, and if you really don't want spare 2.5 hanging around then take it to be scrapped if you really must, or better yet save it for another job.

Damn, beaten again!

 

[JohnD]

or flog it on fleabay

 

[dannyboi2003]

For gods sake do the job properly and use the 1.5mm t&e! 2.5mm will be a pig to work with and will be awkward to connect to switches, fittings etc. From a safety point of view there is nothing wrong with using 2.5mm t&e but its just plain daft, why do people always seem more concerned with saving a few pounds rather than do the job properly!

Lights are not wired as rings as they generally carry a low load and having them connected as a ring would be pointless. However from a regs point of view there is nothing to say you cannot do this and i believe in some commercial premises they may be wired as rings to overcome voltage drop and earth loop issues. But in a domestic situation they would always be wired as radial circuits.

 

[edenbridge]

Ok everybody, I'm using the 1.5mm² for my lighting radial so that it can be identified properly.

However I still want to run a 'busbar' type feature down each side of the loft, so that all the electrics can be easily identified and accessible (and not being toasted amongst the fibreglass insulation). Making the connections can be done at a nice working height, and the whole job would look tidy(ish).

I had planned to spur off this 1.5mm² busbar using junction boxes strategically located along the radial, but then it occured to me I could use ceiling roses instead.

I appreciate this involves more cable to go from the switch to the rose/junction box, and then back to the point where the light fitting is to be positioned (this could be anything from downlighters, ceiling fans, pendants - we just haven't decided yet!)

Other than the extra length of cable (of which I have oodles) is there anything wrong with this approach?

Thanks again[/img]

 

[holmslaw]

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[edenbridge]

Do you invent wheels for a living?

No, I'm a draughtsman, but I like an easy life when it comes to wiring! I can't be doing with cables zig-zagging and criss-crossing the joists, getting tucked under/over other cables and pipes. I'm just a bit anal when it comes to tidy wiring.

I don't think you have understood the previous comments!

I'm using 1.5mm² to prevent cretins in the future from fitting 16A MCBs to a lighting circuit. Why they would is beyond me - everything will be clearly marked!

All the cable in any circuit should be the same size/curent rating.

Really? Even down to the switches and fittings?? I thought the 1.5mm² was for long runs, and 1.0mm² for shorter sections.
Some pendants only have 0.75mm², don't they?
My in-laws lighting circuit was wired completely with 1.0mm² - that's where I've acquired the bit reel from!

You should be using a loop in system (see wiki)

I don't think you've understood my plan, this IS a loop-in system. It's just stretched out into a straight line with longer cables between the switches and fittings. I don't want to spur off to the fittings with junction boxes any more - the conveniently located ceiling roses WILL be the junction boxes

PS - what did use to do the drawing?

MS Paint

 

[lazygit]

the conveniently located ceiling roses WILL be the junction boxes

Surely junction boxes would be better than ceiling roses
A ceiling rose has cable entries from the rear so do you plan to drill holes in the beams?
Correct me if im wrong but I thought it was not allowed

 

[holmslaw]

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[Lectrician]

Your plan sucks.

I would use 1mm or 1.5mm all the way.

For a simple circuit, loop in and out of the ceiling roses with a drop to the switch. If this becomes a mess with zigzag'ing between joists, and cables wrapped around pipes, then you obviously should not be attempting to install cables.

Around 90% of homes use a loop in/loop out method at the lighting points. Are you saying your method is superior? It really isn't.

 

[edenbridge]

Surely junction boxes would be better than ceiling roses?
A ceiling rose has cable entries from the rear so do you plan to drill holes in the beams?

Good point, forget the ceiling rose idea. I certainly have no plans to drill through joists or beams.

I would use 1mm or 1.5mm all the way.

1.5mm² for the loops and 1.0mm² for the drops, is OK though, isn't it?

If this becomes a mess... then you obviously should not be attempting to install cables.

I've got an opportunity to 'get in first' and put my wiring where I want it so it will still be accessible. I've been in enough lofts to see how it shouldn't be done, and also how an electrician has done things properly, but only enough to make his life easier, and without regard for things that get added by others later, such as insulation and central heating pipes. I don't mind spending my own time putting cables where I want them.

Being the draughtsman I am, I'm just trying to think ahea
d.

Your plan sucks.

It's still a loop-in/loop-out approach, just pulled straight, so to speak. I think if I had more time to explain it more with diagrams and photos, you might be impressed!

You have come here for advice and you've been given good free advice.
You seemed determined to ignore the advice...

I appreciate all the advice I get on these forums, it's just that I don't seem to be make myself understood so well. I haven't proceeded with my "plan" as yet, which is why I'm asking all these questions before I start, just to see if it's one that's been tried before.

...and are also becoming sarcastic.

Your response this morning was appreciated, but the tone wasn't. The words kettle and black spring to mind.

 

[holmslaw]

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[RF Lighting]

I would use 1mm or 1.5mm all the way.

1.5mm² for the loops and 1.0mm² for the drops, is OK though, isn't it?

NO!

FFS

How many times do we have to tell you?

 

[333rocky333]

Some pendants only have 0.75mm²

Yes they do, however that is not really classed as the fixed wiring, and rarely more than a metre long.

The fixed wiring, in your case the twin and earth is usually the same size throughout.

Technically, both 1mm and 1.5 are both capable usually of carrying 6 amp for a lighting circuit,but both have different resistance per metre,
so if mixed on the same circuit, it would make it more difficult, to work out volt drop etc.

It would also make testing difficult as what would you write down for the conductor size.
I can see what you are trying to achieve ,if you use junction boxes that are accessible and providing the total length of cable is within the maximum volt drop I can not see a problem.

Using 1.5 will give you a greater maximum length than 1mm