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Discuss TT and RCD protection in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. essex
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    essex Electrician's Arms

    Location:
    Wiltshire
    Just noticed that the requirement for RCD protection has been removed for TT installations.
     
    • Informative Informative x 1
  2. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    RCD protection for what? The whole installation?
     
    • Optimistic Optimistic x 1
  3. essex
    Offline

    essex Electrician's Arms

    Location:
    Wiltshire
    Yeah. The requirement for RCD protection has been replaced with an option for RCD protection or on OCPD. For an OCPD to be used the Zs must be 'permanently and reliably assured'.
     
  4. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    Really?

    That doesn't sound right .......
     
    • Like Like x 1
  5. Strima
    Offline

    Strima Electrician's Arms

    Location:
    St Neots
    Which reg you looking at?
     
    • Like Like x 1
    • Funny Funny x 1
  6. DPG
    Offline

    DPG Electrician's Arms

    Location:
    S Yorkshire
    Come on - don't drip feed stuff to us, give us some proper detail.
     
    • Agree Agree x 1
  7. Risteard
    Online

    Risteard Electrician's Arms

    Location:
    Derry, Ireland
    Business Name:
    Walsh Electrical Services
    The 17th did that. RCD protection has not been mandatory for a TT system since the 16th Edition.
     
    • Agree Agree x 4
    • Like Like x 1
    • Informative Informative x 1
  8. essex
    Offline

    essex Electrician's Arms

    Location:
    Wiltshire
    411.5.2 -

    'One or more of the following types of protective device shall be used, the former being preferred:

    (i) An RCD
    (ii) An overcurrent protective device.

    NOTE 1: An appropriate overcurrent protective device may be used for fault protection provided a suitably low value of Zs is permanently and reliably assured.

    NOTE 2: Where an RCD is used for fault protection the circuit should also incorporate an overcurrent protective device in accordance with Chapter 43.'
     
  9. Risteard
    Online

    Risteard Electrician's Arms

    Location:
    Derry, Ireland
    Business Name:
    Walsh Electrical Services
    Yes, but the 17th had the same requirements. The 16th Edition mandated RCDs for fault protection as I recall, but the 17th definitely didn't.
     
  10. happyhippydad
    Offline

    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    Essex, you're always (or rather 99.9% of the time) going to need an RCD for TT as you'll never be able to meet the Zs values unless the Ra<1Ω which (unless you are Trev) is nigh impossible.

    I'm pretty sure that reg you have given was in the 17th, so nothing new. Would be very interesting to know if anyone on here has ever been able to get an Ra low enough to forgo an RCD on a TT though?
     
    • Like Like x 1
    • Disagree Disagree x 1
  11. Risteard
    Online

    Risteard Electrician's Arms

    Location:
    Derry, Ireland
    Business Name:
    Walsh Electrical Services
    Precisely. It's a decade new.
     
  12. sinewove
    Offline

    sinewove Regular EF Member

    Location:
    shipley
    Once got an RA of 6 ohms on a steel farm building by drilling and tapping a girder for the lug.Would have been ok for a B6 on a lighting cct I think.
    Regards S
     
    • Like Like x 2
  13. essex
    Offline

    essex Electrician's Arms

    Location:
    Wiltshire
    I would bed to differ. The last TT system we tested was 0.73 and that was only a single rod.

    Although I do agree it is unlikely to be ever able to prove a permanently and reliable Zs on a TT system it does loosen the requirements a little and in this case a 500mA RCD would be more than enough.
     
    • Old Old x 1
  14. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    The trouble is even if you did achieve TN values then you would also have to be 100% confident that it would be consistent.
     
    • Agree Agree x 2
    • Like Like x 1
  15. spinlondon
    Offline

    spinlondon Trusted Advisor

    Location:
    Harlow Essex
    Was never required.
     
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