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Discuss Obtaining R2 value on RFC in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    If for whatever reason you can't do an R1+R2 test on a ring final circuit (unable to identify opposite legs). There's also an option on the paperwork for the R2 value...

    Am I correct in thinking that you do an end to end test on the CPC's which would give you r2, then just divide it by 4 to give you R2?
     
  2. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Yes but what about your continuity tests end to ends on the ring final?
    If it's periodic testing then just take the zs at each socket.
    If it's initial verification then continuity needs to be established/verified so R1+R2 shouldn't be an issue.
     
  3. Pete999
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    Pete999 Trusted Advisor

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    no because you will not have cross connected and tested the RFC correctly, why the difficulty in identifying the RFC legs?
     
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  4. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    It's just a minor works (socket replacement).
     
  5. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Just test zs and just to ease your mind do continuity check at the socket your replacing end to end of conductors, unless it's a spur.
     
  6. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    I did continuity of L, N & E at the D.B. I just didn't want to leave a box blank.
     
  7. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    So how come you can do R1+R2 if you've already done end to end readings on the live and cpc especially?
     
  8. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    Yeah you're right I'm being stupid again aren't I
     
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  9. Ian1981
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    Ian1981 Electrician's Arms

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    North east
    Haha long week?
     
  10. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    It's not even over yet lol
     
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  11. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Not till the fat person squeals.
     
  12. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Edit But yeah doing end to end on live and cpcs added and divide by 4 should give you total value of R1+R2 as you have 2 middles which can be considered the end of the circuit if it was a radial and 2 conductors in parallel
     
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  13. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    Thanks for the replies.

    Always appreciated :)
     
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  14. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Following on from the above question consider a situation where you can't readily disconnect the cpc at any point to test it, or doing so is rendered largely pointless by the installation method.

    I'm thinking of a circuit wired in SWA, MICC or steel conduit/trunking.
     
  15. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Your total R2 resistance you mentioned earlier would be your end to end continuity of the cpcs you'd have measured
     
  16. Pete999
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    Pete999 Trusted Advisor

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    If it was a Radial circuit
     
  17. Pete999
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    Pete999 Trusted Advisor

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    If it was a Radial circuit sorry don't know what happened there posted twice
     
  18. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Yes R1+R2 really only works in an all insulated wiring system I guess.
    Method 2 is usually used for conduit systems
     
  19. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Is it now a ring final pete?:D
     
  20. Pete999
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    Pete999 Trusted Advisor

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    So R1 =r1 and R2=r2, R1+R2 =r1+r2 ? is that what you are saying Ian, and cross connecting is out of the window?
     
  21. Zdb
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    Zdb Regular EF Member

    Location:
    UK
    So on a RFC I would divide the end to end of the CPCs by 4 to get R2?
     
  22. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    No I meant you posted twice mentioning a radial so I said now is it a ring?
    Just jesting pete
     
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  23. Pete999
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    Pete999 Trusted Advisor

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    Sorry Ian had a hard day, ran out of vino, visitors all afternoon we didn't want, then JWs arrived trying to preach to me.
     
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  24. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    why do you think it is, can you back it up with a bit of science or is it guesswork?
    With questions like this you'll understand it better if you logically think through and work out the answer first, then ask the forum to confirm it or otherwise
     
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  25. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Remember we have a divider of 4 because we have in effect to mid points furthest points and 2 cables /conductors in parallel
     
  26. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Why even bother with a cert for an accessory change?

    Zs test , note value on invoice.

    Tin hat and 3d glasses on
     
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  27. ye oldie sparks
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    ye oldie sparks Regular EF Member

    Location:
    sussex
    When we do ring main testing and find that all the earths are twisted together in the consumer unit, usually with no sleeving, and you can't identify the pairs going out of the board. We remove and disconnect a socket and split all cables, define the cables coming in and going out, you can then carry out the proper testing procedures on the ring at the this point.
     
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