Testng Earth loop on 6A proteus MCB

Discussion in 'Electricians' Talk' started by e30mark, Apr 9, 2006.

  1. e30mark

    e30mark Member

    Hi guys,

    Keep having problems testing 6A Proteus type B MCB's on lighting circuits.

    Using a Megger MFT1502 on 'no-trip' Earth loop setting, and using the 2 & 3 wire methods, either the MCB trips, or the meter trips... only seem to have this problem with proteus MCB'S... any one else have the same problem using a Megger & Proteus together? a mate came round with his MFT1502/2 and we both got the same results.

    I have disconnected the load from the breaker and tested the MCB by it's self and it still trips out... had this in two properties now! all OK on 16A and above MCB's

    How much current does a Megger MFT deliver on the 'no-trip' loop test ???

    Any thoughts ?
     
  2. X

    X New Member

    Errrrrrrrr........

    A tiny little thought arrises, have you read the Megga instruction book for this test.
     
  3. X

    X New Member

    You will kick your self when you do....
     
  4. X

    X New Member

    But just incase you can't find it, heres an extract from the data sheet... which may be helpfull

    LOOP TESTING
    ¦ Low current loop test is a 3 wire non-tripping
    0.01 O loop test designed to prevent RCD tripping by
    using a sophisticated 15mA loop test pioneered by
    Megger Limited. This NO-TRIP test ensures the RCD will
    not trip whilst performing a loop impedance test.
     
  5. russ295

    russ295 New Member

    sure i read this somewhere on this site, take out the 6a mcb, replace with a 10a or 16a, do the test and then replace with the 6a, shoot me down in flames if i am wrong, but somebody has mentioned this before.
    russ
     
  6. tallow nob

    tallow nob New Member

    Do the no trip test.

    Use 3 leads.

    Phase in Bottom, Earth in middle and Neutral in top ports.

    Ensure there are no other lamps lit on the circuit you are testing.

    Try it and see.

    TN
     
  7. e30mark

    e30mark Member

    But just incase you can't find it, heres an extract
    from the data sheet... which may be helpfull

    LOOP TESTING
    ¦ Low current loop test is a 3 wire non-tripping
    0.01 O loop test designed to prevent RCD tripping by
    using a sophisticated 15mA loop test pioneered by
    Megger Limited. This NO-TRIP test ensures the RCD
    will
    not trip whilst performing a loop impedance test.

    cheers Pengu, it's the MCB & or the Megger that is tripping, not a RCD...

    Been back there today to finish off a few bits, i had a play with the CCU......

    If i wire a socket off the 6A MCB and plug in my MFT1500 using the plug top lead all is well. If i connect my tester using 3 separate leads to phase, neutral & Earth it trips out!

    I'm sure the answer is staring me in the face, but lack of sleep & 20 days work on the trot has got to me. I'll take a look at the instructions again tomorrow...

    Cheers
     
  8. chill-man

    chill-man New Member

    i have had the same problem with some 6A mcb's,can't remember which make,as said previously temporarily fit a larger mcb and do your test.
     
  9. X

    X New Member

    Low current loop test is a 3 wire non-tripping
    0.01 O loop test designed to prevent RCD tripping by
    using a sophisticated 15mA loop test pioneered by
    Megger Limited. This NO-TRIP test ensures the RCD will
    not trip whilst performing a loop impedance test.

    High current loop test.. at 25 A provides a fast loop test
     
  10. e30mark

    e30mark Member

    I feel one of us is missing the point here, it's not the RCD that is tripping, its the MCB when using a 3 wire test, if i try a 2 wire test the meter trips.

    I'll just fit a larger MCB and re-run the earth loop test...
     
  11. sparkin!

    sparkin! New Member

    ReTesting Earth loop on 6A Proteus MCB
    Posted: Apr 10, 2006 8:46 PM Reply


    <i a=" and=" earth=" feel=" fit=" i=" if=" is=" its=" just=" larger=" loop=" mcb=" meter=" missing=" not=" of=" point=" rcd=" re-run=" test=" test...=" that=" the=" trips.=" try=" us=" using=" when=" wire=">

    Not really recommended, in testing!
    WHY, not calculate z,s?[/i]
     
  12. mutton

    mutton New Member

    ive also had the same problem, i usually temporarily replace the mcb for a higher rated one for the the duration of the test.
     
  13. tallow nob

    tallow nob New Member

    Far easier to just stuff the tail into another MCB on the same bus bar...


    TN
     
  14. state-it

    state-it New Member

    I've rewired 3 of my neighbours houses using the same Crabtree boards. One of the installations, my Megger LCB2000 tripped one of their 6A circuits. But not any other 6A Circuits on any other installations. It kept doing it., so I calculated Zs.

    I didn't swap MCBs or anything like that, but reading this thread has just made me think about it all again, and I'm thinking now was it a just a duff MCB? Do all your 6A Proteus MCBs trip?
     
  15. tallow nob

    tallow nob New Member

    Measured Zs is by far the better way to go.

    Calculated is not really a proven result and I doubt any Part P scheme provider would approve of it. I know both NAPIT and NICEIC would take a dim view of it as standard practice.

    At the end of the day you are filling out a schedule of inspections and test results - not test calculations, guesses or what it should be's.

    The mcb in place for the duration of the test is of no consequence whne taking the measurement so just use a higher rating for the duration - or even move away from using pony gear like pooteus?

    TN
     
  16. X

    X New Member

    or Megger !
     
  17. sinewave

    sinewave Screwfix Select

    Nowt wrong with Megger me owd feathered one!


    Far better than the namby pamby leads yer get with ya Flukey Fairy gear! ;)
     
  18. tallow nob

    tallow nob New Member

    I loves my Megger you can poke your Fluke up yer pooper.

    TN
     
  19. X

    X New Member

    Hahahahah...
     
  20. X

    X New Member

    I had a feeling there would be a few insults hurled in my general direction !
     

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