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Discuss RCD Protection for submains in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. TJC1
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    TJC1 Regular EF Member

    Location:
    United Kingdom
    Evening all

    We have been asked to do some redial work picked up by a testing company i a hostel. It has been picked up that is no RCD protection in the rooms

    There are 5 submain circuits that feed the 20 consumer units, 4 consumers units per submain (B32) Each room have a consumer unit which has two double sockets off a 16a radial and a lighting.

    They asked my advice on whether to change the submain MCB to RCBOs or whether to change the consumer units for main switch and RCBOs

    They supply cables to each consumer unit are above a plasterboard ceiling but cant be sure of the installation method, does the submain need to be RCD protected? As i dont want to put RCBOs on each circuit and also on the submain also

    Thanks
     
  2. essex
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    essex Forum Mentor

    Location:
    Wiltshire
    If the installation method of the sub-main requires RCD protection then how will fitting RCBOs on the final circuits protect the sub-mains?
     
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  3. TJC1
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    TJC1 Regular EF Member

    Location:
    United Kingdom
    That's my question, do the submains need to be RCD protected? Seems ridiculous that i need to install an RCD on the submain when it protects 4 consumer unit. It would be much better to be able to install separate RCBOs on the consumer unit and leave the submain.

    Does above plasterboard ceiling count as buried? Or require an RCD
     
  4. spinlondon
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    spinlondon Forum Mentor

    Location:
    Harlow Essex
    Whilst cables above ceilings and below floors require additional protection where they pass through joists or battens. RCD protection is not an acceptable method.
     
  5. snowhead
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    snowhead Respected Member

    Location:
    Mildlands
    If you screwed a 50mm screw into the ceiling would it hit the Submain anywhere along it's length?
     
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  6. TJC1
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    TJC1 Regular EF Member

    Location:
    United Kingdom
    How would you get over my issue?
     
  7. 45140
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    45140 Regular EF Member

    Location:
    Wales
    The answers you seek are in BS7671
     
  8. FLICK
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    FLICK Electrician's Arms

    Location:
    Essex
    What type of cable are the subs and what edition of the regs was the original work done to?
     
  9. spinlondon
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    spinlondon Forum Mentor

    Location:
    Harlow Essex
    Seems to me, that you have been asked to supply RCD protection for the rooms.
    I’m assuming that’s for socket-outlets and circuits of locations containing baths or showers?
    You can either install an up front RCD for each room, or swap MCBs for RCBOs.
    How you do that is up to you.
     
  10. TJC1
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    TJC1 Regular EF Member

    Location:
    United Kingdom
    Im not sure on the depth and the cable is T&E
     
  11. essex
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    essex Forum Mentor

    Location:
    Wiltshire
    I have just re-read the op.

    The EICR that was done has highlighted a lack of RCD protection on final circuits on all CUs.

    The client is trying to cut costs by asking if fitting ‘up front’ RCDs on the sub-mains instead of the CUs therfore installing five RCBOs rather than 40.

    This is not an option due to selectivity so I would say no to that.
     
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  12. spinlondon
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    spinlondon Forum Mentor

    Location:
    Harlow Essex
    If the cables are just laid on plasterboard, there’s no requirement for a minimum depth.
    The drill through the plasterboard, the drill will push the cable away.
    Where cables run through joists or battens, the drill can’t push the cable away, so additional protection is required.
    1.Depth between cable and the surface of the floor or ceiling has to be greater than 50mm.
    2.Earthed sheath, conduit or trunking.
    3.Steel plate between the ceiling/floor and the joist/batten.
    Unlike for cables concealed in walls, RCD protection is not an option.
     
  13. FLICK
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    FLICK Electrician's Arms

    Location:
    Essex
    My take on this is that if it was installed to the 16th edition or before then the sockets don’t require the additional protection unless they could be reasonably expected to be used for outdoor equipment.
     
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  14. spinlondon
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    spinlondon Forum Mentor

    Location:
    Harlow Essex
    Yes, that’s correct.
    Only started needing RCD protection when the 17th came in, as they would be used by unsupervised ordinary persons.
     
    • Agree Agree x 1
  15. FLICK
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    FLICK Electrician's Arms

    Location:
    Essex
    The thing is we don’t know when it was installed. We also don’t know if the guy who issued the report is aware of the changes between the 16th and 17th. My point is that I’d like to know these facts before banging in RCD’s.
     
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