Taking two spurs from ceiling rose

[cbon90]

Hi all, I hope we have some knowledgeable sparkies who can comment on this one. I will start off by saying that I am confident and skilled in most areas of DIY and am not stupid when it comes to electrics - I have enough understanding to stay safe and know my limits. I think this one is within my capabilities so I don't want to hire an electrician, but I need this sense checked.

My electrics knowledge does not cover complicated lighting loops, however! The room in question is the upstairs hall, which has one pendant light controlled by 3 switches (one downstairs, two upstairs). The loop is therefore too much for my comprehension! What I want to achieve is to retire the pendant and install two up-lighters instead. When I open the rose, I can see that the pendant is just a live and neutral going to brass screw terminals. The earth terminal is currently unused, but I know I will need this moving forward. My hope is to ignore the complicated loop wiring which I know nothing about, and simply utilise the humble brown, blue and green/yellow cables that are within my comfort zone.

Can I run two cables (one to either side of the room) from the same brass terminals the current pendant connects to? My idea is to use the existing rose effectively as a junction box, and shove it above the ceiling into the attic, plastering over its hole and forgetting the pendant was ever there, whilst running two new cables across the attic to my new up-lighters.

I have attached a crude diagram which I hope explains all!

Many thanks!
Chris

 

[flyingsparks]

Yes you can do as you suggest, however rather than shoving the rose up above the ceiling, use a joint box. Is the attic accessible? If not a maintenance free joint box would be required.

 

[winston1]

Lights are not loops, they are spurs.

 

[bernardgreen]

Lights are not loops, they are spurs.

A series of loops does not necessarily mean a ring and lighting circuits are not spurs but radials but may in a large house be a ring final if voltage drop due to cable length becomes a problem

 

[JohnW2]

Lights are not loops, they are spurs.

I don't think one can meaningfully talk about 'spurs' from a radial circuit - all one can really talk about is a 'branching radial'.

Imagine light A (at supply side of circuit) feeding light B, which in turn feeds lights C & D. Which is the 'spur' - the connection from B to C or the connection from B to D?

Kind Regards, John

 

[EFLImpudence]

See definition of 'spur' in Part 2.

 

[JohnW2]

A series of loops does not necessarily mean a ring and lighting circuits are not spurs but radials but may in a large house be a ring final if voltage drop due to cable length becomes a problem

I think that it would have to be an very large house for VD to become a problem. By my reckoning, if one assumes that a full 6A load (unlikely) is evenly distributed along a radial lighting circuit, then you could have about 80m of 1.5mm² cable before VD rose to more than the magical 3%.

Kind Regards, John

 

[JohnW2]

See definition of 'spur' in Part 2.

We've been through this before. I know what that definition says, but it is meaningless/unworkable in the case of a radial circuit.

As I just asked, if a radial branches, which of the branches are you going to call the 'continuation of the radial' and which of the branch(es) are you going to call the 'spur(s)'??!

Kind Regards, John

 

[EFLImpudence]

It's like a tree, once past a certain point they are all branches.

 

[JohnW2]

It's like a tree, once past a certain point they are all branches.

So you believe that the 'radial' itself ceases to exist at the first branch?

Kind Regards, John

 

[EFLImpudence]

No, it's all a radial.

 

[JohnW2]

No, it's all a radial.

So what (if anything) is "a branch from a radial" (the BS7671 definition of a 'spur')??

Kind Regards, John

 

[EFLImpudence]

So what (if anything) is "a branch from a radial" (the BS7671 definition of a 'spur')??

The same as a branch from a tree. The tree is nearly all branches but it's still A tree.

 

[cbon90]

Ok thanks for the meaningful replies on voltage drops - I respectfully ignore the quibbles about terminology - I am not an electrician myself and I wholeheartedly apologise for misusing the term "spur" which I thought was accurate enough for the purpose. Life must go on, however.

Regarding the size of my house, its a 4 bedroom detached and there are 7 light fittings upstairs. If someone can help me address the voltage drop question based on this, I would be very grateful. And please, no more nitpicking about jargon!

I am sure I could confuse most people here with a whole load of IT-related and computer programming jargon, but it wouldn't help anyone would it? Let's call a cable a cable and see if I can get an answer about joining two of them together.

 

[ban-all-sheds]

My electrics knowledge does not cover complicated lighting loops, however! The room in question is the upstairs hall, which has one pendant light controlled by 3 switches (one downstairs, two upstairs). The loop is therefore too much for my comprehension!

Sorry to rain on your parade, but that is not in any way "complicated".

My hope is to ignore the complicated loop wiring which I know nothing about, and simply utilise the humble brown, blue and green/yellow cables that are within my comfort zone.

You really ought to make the size of that zone larger.

• http://www.google.co.uk/search?q=electrical+circuits+(basics+OR+101)
  
• http://www.google.co.uk/search?q=uk+house+wiring+(basics+OR+101)
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
• [wiki]Electrics%3ALighting[/wiki]
  
• [wiki]Electrics%3Abooks[/wiki]
  
• [wiki]Electrics%3Aindex[/wiki]