Junction box with more than one light

[antgel]

Hi all,

I'm rewiring part of my lounge light circuit to include six small lights which will be switched on and off in two's by the switches on a three-gang switch. I've never done lighting before, but here's what I propose after a good read of Collins.

Use three junction boxes, one per pair of lights. Each box to have a cable to the switch and two more cables, one to each light. Permanent mains to be daisy chained through the three boxes.

Is there a limit to the number or lights that should come off one junction box? Is it better to use one box per light? I ask as I plan to extend the kitchen circuit to three fittings, all quite near, and it seems that one box could do it for all three.

Antony

[Owain]

The limit is whether the cables will physically fit. Lighting circuits are radials so there is not the issue of point loads that has to be considered with rings.

2 lights per JB seems sensible and reasonable.

Kitchens is Part P.

Bear in mind that *each* point on a lighting circuit must be considered to be 100W or actual load if greater, with no diversity. The assumption is that all the lights could be on at the same time. Max load on a 5/6A lighting circuit is about 1200W or 12 points, so unless your circuit is already very lightly loaded you will probably be non-compliant with the Regs.

Owain

[John Rumm]

Five cables will fit a standard 4 terminal JB without any problem. Use

1.0mm sq cable and not 1.5mm though to make it less of a squeeze

There is also nothing to stop you daisy chaining the switched live from the first lamp holder to the second rather than running a second dedicated wire back to the JB. That way you only have the standard four wires per JB.

[Christian McArdle]

If it fits in the hole and you can still get the cover back on, it's OK.

Christian.

[antgel]

By "point" do you mean junction box (or rose on a loop-in system)?

It is lightly loaded. I have two circuits in an 900sqft two-bed flat. The circuit in question currently carries about 600W tops (proably nearer 400).

Antony

[antgel]

Like it, thanks.

[Martin Angove]

I had always read that one as only applying to standard BC/ES fittings. If the lights in question are LV then they'll be limited by the transformer to Watts and that's the figure I'd use. If they are GU/GZ10 then the fitting usually has a (heat-related) limit, often 50W (though I believe 75W GU10s are available?) so again, I'd use that rather than 100W. Likewise R63 bulbs are very difficult to find above

60W, and the fitting may not be rated above that anyway.

Works for me anyway :-)

Hwyl!

M.

[Andrew Gabriel]

It's not in the Regs. It's a recommendation in the On-Site Guide. As with any of the diversity calculations, it's a good starting point if you have no other information to go on. If you know the current and future usage doesn't fit those recommendations, then you should design appropriately.

(Some of the diversity recommendations are showing their age now;-)

[antgel]

They are GU10. I'm still confused by the meaning of "point" in Owain's post.

Antony

[antgel]

When you say "daisy chaining the switched live", you mean connecting live and neutral (and earth in this case) for the second light to the three terminals on the first light? Or are the earth and neutral of the second light handled differently?

And another thing. For the kitchen, which is three lights off one switch, can I use the one junction box then daisy chain the second _and third_ lights? I assume as it's a radial that I can - it's not like daisy-chaining spurs on a ring circuit, but I'd love a quick confirm. :)

[Owain]

However if the LV fitting is replaced by a standard mains one ...

In such circs I would treat the transformer as one point, as 100W min.

Owain

[Owain]

I mean ordinary rose, or luminaire. A 5 x 40W electrolier would be 200W not 500W.

Fairy nuff. I just didn't want you (or anyone in the future reading the archives) adding another seven lamps to an already max-loaded house circuit.

Owain

[Owain]

antgel wrote: > When you say "daisy chaining the switched live", you mean connecting

Yes.