Ring circuit for LIGHTING

Discussion in 'Electrics UK' started by sparkwright, 13 Nov 2021.

  1. sparkwright

    sparkwright

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    We often receive posts from people claiming the lighting in their home is on a ring circuit, when in reality it's on a normal radial, and we generally get someone who corrects them.

    But we are also reminded that lighting can be on a ring circuit, particularly in industrial or commercial environments.

    We are also told lighting can be on a 16amp circuit.

    I've not knowingly encountered a lighting circuit that has specifically been designed as a ring circuit.

    What is the advantage of this, and how do you know when to stop 'spurring' off this ring, as I imagine to much spurring makes having a ring pointless?
     
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  3. EFLImpudence

    EFLImpudence

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    The point is a lighting circuit designed as a ring would only be for EFLI reasons and possibly volt drop - hardly necessary in a domestic situation.

    The CCC of the cable still has to be greater than the rating of the OPD.

    So it is not the same as the UK socket ring circuit whose special dispensations still relate to BS3036 fuses and would not now be necessary with 32A cable or 27A MCB,



    Also I get the impression some poster think ring is just another word for circuit; not necessarily meaning it is connected in a ring.
     
  4. sparkwright

    sparkwright

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    So would such a ring be used only on a two plate system?

    If in a conduit system with singles, the neutral could easily continue all round the lights as a ring, the earths too.

    From the output side of the switch, the lives going to the lights would presumably be in a radial form?

    ***

    If wired in SWA for example, two plate, the ring would only extend to the switches - then an SWA going to the lights as radial?

    Not a lot of info on this, not very recognised IMO.
     
  5. EFLImpudence

    EFLImpudence

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    I am not sure what you are getting at.

    As the CCC of the cable has to be greater than the rating of the OPD, there is no point wiring it as a ring unless the circuit is very long, as in commercial situations, and a reduction in Zs is required.

    In domestic situations, if it ever arose (surely unlikely with 6A MCB), then it would probably be easier to increase the size of the cable - or split the circuits.
     
  6. sparkwright

    sparkwright

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    I was just wondering if I was in an industrial or commercial environment, and someone asked me to wire all these lights in a ring, as I'm told can be done, how I would actually do it.

    I've never seen or done a lighting ring, wondered 'how' it's actually done.

    I take on board it's rather pointless if the cable capacity is greater than the OPD, yet it has been said lighting can designed as a ring.
     
  7. EFLImpudence

    EFLImpudence

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    The same as domestic socket circuits.

    You just have to calculate the Zs.

    You could wire a cooker circuit in a ring but it would be entirely pointless to run the cable back to the CU.

    If it were not for the 'outdated' UK socket ring dispensations, you would not have thought to raise these questions.
     
  8. ericmark

    ericmark

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    Ring final and ring are not the same, we had lighting in a ring so a section could be isolated to work on it.
     
  9. sparkwright

    sparkwright

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    You say you would wire the lighting ring the same as a domestic socket circuit. How do you do that with a two plate conduit system?
    The earth and neutrals would be in a ring throughout. The lives in a ring to the switches. From the switches, the live to all the various lights wouldn't be on a ring?

    Is that how you would wire it?

    And on a system using regular two core and earth cable, two plate, the ring only extends to the switches only - is that right?

    This thread was not created primarily because of the thread about socket ring circuits, it was always my intention after regularly reading comments from someone here, I can't remember his name but he's not very bright, who says lights are never ever wired in rings, and then gets blasted by others stating they sometimes are in industrial and commercial environments.
     
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  11. bernardgreen

    bernardgreen

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    A ring circuit for lighting is single fault tolerant. A loose connection in a ceiling rose on a radial would affect lamps between that rose and the end of the radial.

    Access to fix that single fault may be difficult if it is a high ceiling and / or over a stair well. A ring would keep all the lights operational and prevent / reduce arcing at the fault.
     
  12. sparkwright

    sparkwright

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    Ah, so everything past the light switch, ie to the light, would be on a ring too?

    But that's not the point of a lighting ring circuit though, is it - purely to keep the lights working if there's a bad connections that's being ignored?

    I thought it was more to do with Zs, voltdrop, and all that?
     
  13. bernardgreen

    bernardgreen

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    No only the looping on Live and Neutral.

    Maybe I should have added that not all single fault would e tolerated. A loose connection could affect just one lamp and leave that lamp non functional
     
  14. EFLImpudence

    EFLImpudence

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    ...but that is only acceptable because the CCC of the cable is greater than the OPD.

    As Eric said a light circuit (or any other circuit) wired in a ring is not the same as a UK socket ring (final) circuit.
     
  15. Adam_151

    Adam_151

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    Exactly this. I have never seen a lighting ring in commericial or industrial but I could see that in a small number of situations, they might be a way to address v/drop or zs issues, I have seen one in domestic where it was clear that it had been done by someone who mistakenly thought it needed to be a ring, I started to become a bit confused when I couldn't find the end of line of either of the two legs in the breaker then it was "I wonder if..... surely not.... yes it is, bloody hell why have they done that?"

    What I have seen is a multi-destination submain wired as a a ring... a large 4 core ran around the site calling at the glasgow main switch for each building, I suspect again for V/Drop and zs issues, and partly because I imagine the designer had probably worked for the electricity board at some point and decided that a ring feeder had advantages. I can't know for sure, AFAIK it went in the late 60s so I doubt hes still around
     
  16. JohnW2

    JohnW2

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    I don't see why having it as a ring makes that any more possible/easy. What am I missing?

    Kind Regards, John
     
  17. JohnW2

    JohnW2

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    All true, but is "single fault tolerant" necessarily a desirable (or even necessarily 'safe') thing?

    With such a situation, once the 'first fault' has occurred, no-one will be aware of it, so one is (unknown to everyone) back to the situation in which one (further) fault will disable the circuit.

    Kind Regards, John
     
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