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  1. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    Hello,

    Im confused as to why I'm getting a high zs value at the socket but all r1 rn r2

    ze is 0.5 but zs is .98

    The other problem is a had a rcd won't trip but for some reason when something is plugged in it trips the other rcd.

    All circuits bell out and test fine so could it be the rcd that is playing games with me ?
     
  2. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    RCDs don't play games, they react to a current imbalance. The symptoms you have described are of a reasonably common fault and a bit of logical thought and application of your knowledge of the fiends of electricity should make it clear.
    You almost certainly have a N-E earth fault.

    I don't see what the problem with your Zs reading is??
     
    • Agree Agree x 1
  3. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    What was your r1, r2 and (R1+R2) results for the circuit?
     
  4. chris butterfield
    Offline

    chris butterfield Cecochris

    Location:
    leeds
    Yeah thought it was N EARTH FAULT but what has confused me is all the circuits are in the correct side of the rcd ways but the other rcd tripped !!!!!!
     
  5. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    Am i correct in saying that if i had a n earth fault then the rcd won't trip anyway ?
     
  6. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Is this a new install?
    You may have neutrals crossed somewhere on one rcd but the live from the other rcd assuming it's a dual rcd consumer unit?
     
    • Agree Agree x 1
  7. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    You have a neutral-earth fault on a circuit that's covered by the RCD that's tripping.
     
  8. Pete999
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    Pete999 Trusted Advisor

    Top Poster Of Month

    Location:
    Northampton
    What was the R1+R2 reading?
     
  9. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    Yes its a new install.

    The circuit that trips is tripping the other rcd. Could be i have a N crossed ?

    Looks like ill re test in the morning

    Basically then i have a N/E FAULT ?
     
  10. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    But why is the other red not tripping on test ?

    Is this down to the N/E FAULT ?
     
  11. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    If a circuit on one side of the rcd trips the other rcd then yes you've crossed a neutral by the sounds of it
     
  12. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    MMM (n) crossed then.
    Also poss n earth fault on the other red for it to not work on test ?
     
  13. chris butterfield
    Offline

    chris butterfield Cecochris

    Location:
    leeds
    Also think i may need my dialog meter cal as it keeps giving me different zs readings on the same circuit. Not too keen on this dialog 9083p
     
  14. Murdoch
    Online

    Murdoch Electrician's Arms

    Location:
    Woking
    can you spell out what you mean by "bell out" and test Ok

    How many circuits do you have on each RCD?
     
  15. Loki
    Offline

    Loki Trainee Trainee Access

    Location:
    Devon
    You said that the Ze is 0.5
    Im guessing its a tns & not tncs then as its over the 0.35 Ze max



    If using 2.5 (1.5) T&E

    Zs 0.98 - Ze 0.5 = 0.48

    4 ÷ (2.5 + 1.5) x 0.48 = 0.3

    r2 = 0.3 ohms
    r1 = 0.18

    Roughly lol, Am i close?
     
  16. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    Had this two weeks ago in a fire damaged bungalow. I know it sounds implausible to some but a neutral to earth fault on a circuit stopped the RCD from tripping and test button wouldn't work. Dissed circuit in question...RCD now tests fine and test button works.
     
    • Agree Agree x 1
  17. Strima
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    Strima Electrician's Arms

    Location:
    St Neots
    You will more than likely get a higher Zs through an RCD due to it's own resistance and also the test meter puts out a lower current on the no trip setting so the result isn't as accurate.
     
    • Winner Winner x 1
  18. chris butterfield
    Offline

    chris butterfield Cecochris

    Location:
    leeds
    pretty much lol

    I think also my meter is playing uo as I'm getting different zs readings from the same bloody socket aghhhhhhhh need a vino
     
  19. chris butterfield
    Offline

    chris butterfield Cecochris

    Location:
    leeds
    pretty much lol

    I think also my meter is playing uo as I'm getting different zs readings from the same bloody socket aghhhhhhhh need a vino
     
  20. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Draw it out and work out where the current will flow,
     
  21. chris butterfield
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    chris butterfield Cecochris

    Location:
    leeds
    Right i recon i have a n earth fault on a lighting circuit on that side of the red and also a crossed n on the other

    I recon this is my problem hammy

    Any ideas on the different zs values I'm getting from my dialog tester on the same socket chaps ?
     
  22. Leesparkykent
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    Leesparkykent You Rock Gmes Staff Member Trusted Advisor

    Location:
    Kent
    @Loki@Loki 2.5 T&E RFC with a R1+R2 reading of 0.48 would give an expected value of 1.15 for r2 and 0.77 for r1.

    1.15+0.77= 1.92

    1.92/4=0.48

    To work it out

    0.48x4=1.92

    1.92/1.67=1.15 for r2

    1.92-1.15=0.77 for r1
     
    • Like Like x 1
  23. Pete999
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    Pete999 Trusted Advisor

    Top Poster Of Month

    Location:
    Northampton
    Are you answering post 3?
     
  24. Loki
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    Loki Trainee Trainee Access

    Location:
    Devon
    Thanks for clearing that.
    Think i was mixing formulas up
     
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  25. Loki
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    Loki Trainee Trainee Access

    Location:
    Devon
    Just noticing the Ze was above 0.35 for tncs & was wanting to work out expected R1 & R2 values
     
    • Like Like x 1
  26. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    I seem to recall, I might be wrong, one of our more eminent members describing a situation where a neutral earth fault on a circuit could trip an RCD that is not protected by?
     
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