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Discuss 2core swa, not earth load end.. TT in the Electrical Wiring, Theories and Regulations area at ElectrciansForums.co.uk.

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  1. robo83
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    robo83 Regular EF Member

    Location:
    London
    Hi,

    Been to a job with a 2core swa supplying the garage.. The swa has been glanded inside house to CU. But the other end in the Garage has had the swa run in plastic conduit with no gland on the swa so unable to test r1/r2.

    However the garage has its own earth rod. So technically the swa is earthed from the house end, with the garage having its own earth rod.

    The garage earthing TT is 37.0ohms, would I note this down as the garage r1/r2 circuit. Accepted with the 1667ohms as rcd?
     
  2. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Is this an EICR, or are you doing some alterations/additions in the garage. What is the house supply?
     
  3. Pete999
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    Pete999 Trusted Advisor

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    Do you mean R1+R2? r1 r2and rn are readings for RFCs (Ring Final Circuits)
     
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  4. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Did you mean to quote the OP Pete :(
     
  5. Pete999
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    Pete999 Trusted Advisor

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    Not sure what you are getting at Middy, just trying to say to the OP that r1 and r2 are readings for r1 Live and r2 Earth as a single conductors, I thought he was meaning R1+R2 or am I getting tangled up somewhere?
     
  6. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Ohh okay
     
  7. jaydub
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    jaydub Regular EF Member

    Location:
    Suffolk
    Robo83, can you not get a croc clip on the armouring at all at the garage end? Then you could measure r1 + r2 this way? Midwest and pete, if that was possible, is that allowed?
     
  8. Pete999
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    Pete999 Trusted Advisor

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    It's R1+R2
     
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  9. jaydub
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    jaydub Regular EF Member

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    Suffolk
    I dont follow...
     
  10. Pete999
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    Pete999 Trusted Advisor

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    You are trying to measure the loop of the L and E conductors correct? Which will give you a resistance reading noted as R1+R2 not r1+r2 a small thing but end to end reading r1 r2 and rn are recorded as RFC readings only, and are end to end readings of the L.N and cpc, get the basics wrong and other things will be wrong as well. Of course if you are insulating the armoring from the garage end why would you try and trying to measure the R1+R2 of the distribution cable.
     
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    Last edited: May 31, 2017
  11. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    the swa earth is not part of the garge earth so R1/R2 is gonna be between L and the Rod E. If I read you right?
     
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  12. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Hum.... Not sure what that would achieve.... Think about what you are testing
     
  13. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    My thought is the garage supply is a circuit off the main db (house CU) and this would have its own loop impedance from the SWA armour, which is its CPC. Then the sub board (garage CU) and the final circuits are the TT bit (?) .
     
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  14. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    He is trying to verify earth continuity to the armour of the cable which is not accessible as it is contained within pvc conduit to isolate it from the TT, this earth continuity is applicable to the circuit from the house and nothing to do with the TT.
     
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  15. Midwest
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    Midwest Electrician's Arms

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    Oxfordshire
    Perhaps we should just wait until the OP clarifies what he/she is doing?

    Edit; job wise
     
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  16. jaydub
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    jaydub Regular EF Member

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    Suffolk
    Wilko has interpreted what I was getting at lol
     
  17. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
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    yeh but is it a circuit or just a piece of cable? Where is the loop hah!
     
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    Last edited: May 31, 2017
  18. jaydub
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    jaydub Regular EF Member

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    Suffolk
    It would be a circuit wouldn't it, I guess it would be protected by an MCB in this scenario? I guess OP needs to clarify that
     
  19. Wilko
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    Wilko Electrician's Arms

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    Well if it ain't a circuit how does current / fault current flow in it? Being creative, I'm thinking it's a >32A distribution circuit with a 5 or 1 sec disc time from 411.3.2.3 or .4 - at least it would be if I'd done it in 10mm :)
     
  20. Vortigern
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    Vortigern Electrician's Arms

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    The MCB in the house protects the cable. The circuit in the garage is separate imho.
     
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  21. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    To the op I don't know the task you are undertaking but the EFLI or R1+R2 for the circuit from the house will be between the line conductor and armour of the cable which has been rendered inaccessible. This is the fault path for said circuit and has nothing to do with the TT arrangement. Whatever you are doing you will have to note the reading as Not Verified with the reasons.
     
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  22. robo83
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    robo83 Regular EF Member

    Location:
    London
    Spot on.

    Appoligise to everyone else for confusion.

    Pete, duly noted.

    The swa has been stripped back and the 2 cores run inside pvc conduit.

    I did a board change after the customer had an EICR report conducted. This wasn't highlighted and only became apparent when I begun testing after the new consumer unit was installed.
     
  23. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
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    Wasn't confusing at all Robo.
     
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  24. robo83
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    robo83 Regular EF Member

    Location:
    London
    Thanks,

    I have put LIM in the box and noted on the EIC.

    They also pulled 2 strands from the other swa (another circuit) and connector blocked it and used as the cpc :/ no idea why they never glanded properly.
     
  25. anthonybragg
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    anthonybragg Electrician's Arms

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    NORTHAMPTON
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    CHARLTEC ELECTRICAL LTD
    Exactly as Wilko said ,don't know regarding the position of the RCD however you will need loop reading /Ze +(R1+R2) to determine that the protective device for the sub-distribution circuit will operate within the maximum time for example if someone should accidently put a spade into the cable.
     
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  26. anthonybragg
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    anthonybragg Electrician's Arms

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    The LINE (live) conductor SWA via the substation etc.
     
  27. Pete999
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    Pete999 Trusted Advisor

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    Will it have any reference to the choice of OCPD? cant see how as it's not being used as a cpc?
     
  28. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
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    Ok so you verified a piece of cable.
     
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  29. anthonybragg
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    anthonybragg Electrician's Arms

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    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    Yes and I then can confirm it is safe to energise in the new consumer unit should there be a fault with the sub-distribution circuit the C.P. device will operate.
     
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  30. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
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    F.H. Electrical
    However the OP was asking about R1/R2 vis a vis the garage assuming I read it right I am tired and somewhat sanguine tonight.
     
  31. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    I'm just into the 2nd glass :)
     
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  32. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Jesus this is over complicated. He cannot verify continuity of the armour because it has been rendered inaccessible.
     
  33. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    The question seems to be about the garage unit
    Not the armour???
    I think I'll leave this subject for now night night.
     
  34. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    His initial problem was not being to access the armour of the supply cable to verify continuity and could he record the TT results for the supply cable, answer, no.
     
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  35. driverman
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    driverman DIY

    Location:
    England
    Not that I'm into testing.....Could not the OP measure the TN Zs at incoming SWA cable at garage consumer-unit? Note reading and subject that reading from the Ze reading obtained at the house consumer unit giving R1-R2.
    Another way...use Method 2 wandering lead, assuming connection can be made onto the end of the SWA armouring using a probe.
     
  36. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    The final connection of the armour is not accessible.
     
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