Ring Light Circuit

Discussion in 'Electricians' Talk' started by RSJ, Jan 20, 2006.

  1. RSJ

    RSJ New Member

    I have had an electrician in as I wanted to add halogen downlighters to 3 rooms upstairs. The circuit is currently a radial circuit feeding 5 rooms. The electrician is telling me that he thinks I should split the current circuit and add a sepaerate circuit to feed some of the rooms so as not to overload the cable. Firstly how many 50W halogen lights is it safe to run off of 1.5mm Twin & Earth and secondly couldn't he just run the circuit and make it a ring circuit like you do on the sockets. This would mean that the cable would be effective under half the load if a ring configuration was used. I understand I would need to uprate the MCB if a ring config was used. I do not really want to have to add another circuit as it would mean changing a 2 year old consumer unit as there are no free MCB slots. This obviously is more work for him and more cost for me!!! I need to have any info handy as he is coming round tommorrow to discuss it.
     
  2. Me owd

    Me owd New Member

    It sounds to me like he is being straight with you.
    I would certainly put a new circuit in and leave the existing alone, you don't have to change your consumer unit he can always put an additional 2-way unit in if your existing is full, better to have it done safe and sleep at night!!
     
  3. RSJ

    RSJ New Member

    That's fair comment. If its what's needed then fine but I just thought the ring option would be more simple and quicker. Anyone else got any views or answers to the questions? Is there any technial reason you can have a ring lighting cicuit? If I don't need to replace the consumer unit then that's a big help as he's insisting that's what's needed.
     
  4. prosparks

    prosparks New Member

    Use LV lighting units.
    Watch for fire and acoustic derating of the ceiling and ensure you buy prewired units with the required BS conformaties.
    regards
     
  5. lastword

    lastword New Member

    RSJ - The regulations allow for all sorts of circuit layouts and technically what you’re proposing would likely be ok. However, it’s up to the circuit designer to show that what he is proposing meets all the regulations. That’s a lot of work and is simply not cost effective for domestic situations.

    That’s why we have a set of standard circuit arrangements for which the base calculations have already been done and are ‘deemed to satisfy’ the regulations provided the associated guidance notes and design tables are followed. So, for example, we can install a 32A ring final circuit with unlimited sockets in 2.5sqmm so long as it only covers 100sqm floor area.

    The design effort behind that is considerable and takes into account laboratory tests on the heating effect in the cable, average duty cycles of washing machines etc, seasonal loading effects, and average household size.

    Before he puts in a ring lighting circuit your man would have to go through a similar exercise to prove that ‘….a small overload of long duration is unlikely to occur.’ (Reg 433-01-01). Whereas, if he puts in a ‘standard radial’ in 1.5sqmm, MCB at 6A and assumes 100W per lamp holder (or actual if fixed load), he can sleep soundly in his bed and you won’t get charged for all that design effort ;)
     
  6. blomster

    blomster New Member

    Is a ring circuit ever used for a lighting circuit ?.
    I'm not a spark but have never heard of this.
     
  7. Defcon

    Defcon New Member

    Rings mains are 13A sockets which have 13A plug pushed into them which have a fuse inside to limit the load. Lighting circuits and light fittings don't.

    I think
     
  8. Lokkars Daisy

    Lokkars Daisy New Member

    RSJ It puzzles me that you can suggest the idea of a ring circuit and yet have to ask how many 50Watt lights can be run off your lighting circuit.

    At a basic level ,the lighting mcb is probably 6amp
    6 Amp is around 1400 Watts or 28x50 watt lamps
    You wouldn't generally load the circuit up to max capacity,but it should in theory be ok.
    There is the possibility you could change the 6Amp mcb for a 10Amp giving you around 2300 Watts /a whoping total of 56x 50 Watt lamps. You would need to discuss it with your electrician.
     
  9. ­

    ­ New Member

    What about the 66% diversity rule for domestic lighting? Not all of these lights will all be on all the time will they?

    How do you know it's 1.5 cable? It could be 1.0mm.

    If it is 1.5 cable and if your mcb is 10a then you could have 2300w of lighting! That's a LOT of light for 5 rooms! Even a 6a mcb will allow 1380w of lights.

    However, at the end of the day it's for the electrician to decide what he's happy with. If you don't like his ideas then you'll have to get someone else. There are many ways to do this and a lighting ring is one of them. Ask him what he doesn't like about that idea.
     
  10. RSJ

    RSJ New Member

    Thanks guys for all your comments.
    Just to answer a couple of the things brought up. It is definitely 1.5mm cable in the circuit, I've had a look. On the question about asking how many 50w lights you can have on a circuit I was just checking what I thought it was (I've done electronics (not electrics) at college but I wanted to prove what I thought it was!!!) Its the old Power = Amps x Voltage equation from what I remember. But with halogen you have to double this because of the regs as I understand it.The only reason I'm asking all this is because I think the guy is just angling to get the consumer unit changed and I just get that feeling that he's taking the mick. Its a bit of a difficult situation as he's the husband of a work collegue and I can't really get out of using him now, hence why I need all the information I can get before seeing him. As I said before if the money needs spending then I'll do it no problem,I just want all the information so I can get the right solution. From what I can gather though ring lighting circuits are not normal practice though? If anyone's got anything to add it would all help. I really appreciate your time in answering. Cheers.
     
  11. gas&lect

    gas&lect New Member

    I have been a sparks for longer than I care to remember and in a domestic situation have never seen a lighting ring circuit in operation. I think your installer is pushing it a bit if i was doing the job the extended installation would be quite safe in my opinion and would be notified accordingly.Would it not be possible to get another estimate and see what a second sparks thinks. Regards Benson
     
  12. suts89

    suts89 New Member

    Totaly agree with gas/elect.

    The moment this guy started talking about a ring light circuit i would seriously be questioning his credentials.

    Youve done a bit electronics, you understand the basics so why dont you give it a go yourself...
     
  13. unphased

    unphased Screwfix Select

    Thanks guys for all your comments.
    Just to answer a couple of the things brought up. It
    is definitely 1.5mm cable in the circuit, I've had a
    look. On the question about asking how many 50w
    lights you can have on a circuit I was just checking
    what I thought it was (I've done electronics (not
    electrics) at college but I wanted to prove what I
    thought it was!!!) Its the old Power = Amps x Voltage
    equation from what I remember. But with halogen you
    have to double this because of the regs as I
    understand it.The only reason I'm asking all this is
    because I think the guy is just angling to get the
    consumer unit changed and I just get that feeling
    that he's taking the mick. Its a bit of a difficult
    situation as he's the husband of a work collegue and
    I can't really get out of using him now, hence why I
    need all the information I can get before seeing him.
    As I said before if the money needs spending then
    I'll do it no problem,I just want all the information
    so I can get the right solution. From what I can
    gather though ring lighting circuits are not normal
    practice though? If anyone's got anything to add it
    would all help. I really appreciate your time in
    answering. Cheers.

    If its a 1.5mm2 T&E on your lighting circuit there is bags of capacity in it for additional light points. And you don't double the load for halogens.

    The standard way to design a lighting circuit is to assume each light point will be 100W minimum. If you know for sure that it is more then use the actual but keep the rest to 100W min. Then you simply add all the light point wattages together and get your total load. Then, as you know, its I=P/V. So, for example lets say you had 12 lights

    1200/230=5.2A

    Now a 1.0mm2 cable will safely carry 6A and it is usual to have a 6A mcb on the board. As you have a 1.5mm2 cable I know you can safely fuse this at 10A. So you can have a lighting circuit of 10 x 230 = 2300A on 1.5mm2 before you need to worry. btw this asumes no other derating factors apply (and in a domestic situation likely as not they wont).

    So, I would say your sparky is over cautious with the advice he has given you and you dont need to split the circuit at all. Just need to sit down and do a few sums like I have done to prove it.

    So to answer your original question, on a 1.5mm2 cable you can have up to 23 lamps at 100W.

    Piece of cake for a good sparks ;)

    UP
     
  14. Rings mains are 13A sockets which have 13A plug
    pushed into them which have a fuse inside to limit
    the load. Lighting circuits and light fittings don't.


    I think

    You think wrong. Ring mains run round the street, under the pavement feeding the houses and shops. Final ring circuits have 13a sockets connected.
    Lastword put it perfectly. There is nothing technically wrong in this
     

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