Lighting circuit geometry

[hjalfi]

I'm installing a wall across an existing room to split the room into two. Naturally, I'm going to need to install another switched light. (Actually a two-way.)

Looking at all the various reference materials it would seem that I need to find a junction box somewhere in the ceiling space and simply extend it; a star and hub arrangement. This disturbs me, as it's exactly the thing that ring mains were invented to prevent --- the junction box I'm tapping isn't in turn connected to another junction box connected to another, etc, until eventually this is all being fed off one piece of red-hot cable.

Can anyone point me at any references on how this is all actually supposed to work?

 

[plugwash]

ring cuircuits are used to reduce the size of cable needed to make a safe 32A cuircuit they are not the be all and end all of wiring.

with lighting cuircuits you can spur as much as you wan't just keep the total load on the cuircuit to less than 1380W for a 6A lighting cuircuit

 

[hjalfi]

Hmm. Fair enough, although it still seems a bit dubious to me --- it basically means that any cable in the circuit must be sufficient to carry all the load of the circuit, right?

 

[big-all]

Hmm. Fair enough, although it still seems a bit dubious to me --- it basically means that any cable in the circuit must be sufficient to carry all the load of the circuit, right?

heeelllooo hjalfi thats 23-- 60w lightbulbs running all at the same time on any one floor

 

[ban-all-sheds]

Hmm. Fair enough, although it still seems a bit dubious to me --- it basically means that any cable in the circuit must be sufficient to carry all the load of the circuit, right?

Yes - that's because the cable is the same size throughout.

What's dubious about it?

 

[HDRW]

Hmm. Fair enough, although it still seems a bit dubious to me --- it basically means that any cable in the circuit must be sufficient to carry all the load of the circuit, right?

That's true, but the answer is in the maths - have a look at the rating (in Amps) of a 1mm^2 T&E cable - you'll find it's well over the rating of the fuse/MCB that you have protecting it. And you may well have 1.5mm^2 cable, so you have even a bigger margin!

Cheers,

Howard

 

[Big_Spark]

Hmm. Fair enough, although it still seems a bit dubious to me --- it basically means that any cable in the circuit must be sufficient to carry all the load of the circuit, right?

It's been working in the UK and all other countries for over 100 years now mate, so I think we have lighting circuits sussed pretty much now.

If you do not understand how the circuit works, that lighting circuits are radials not rings, and that rings are designed for specific reasons, then perhaps you are not the person to be undertaking electrical work...

 

[hjalfi]

Oh, don't worry. I have a healthy respect for electricity. What I'm doing now is making sure that I *do* understand it before doing anything. I just found the fact that lighting circuits are radials slightly surprising given the general anal-retentiveness of the UK electrical regulations, and wanted to get confirmation...

 

[kai]

One way is to run Wall Lights off their own separate B6 MCB, so that if one B6 Lighting circuit trips out when a bulb fails, you will still have light available in the room etc.

 

[ban-all-sheds]

I just found the fact that lighting circuits are radials slightly surprising given the general anal-retentiveness of the UK electrical regulations

Why?

And why do they seem dubious to you in terms of cable capacity when it is actually ring circuits which are dubious, not radials?