Testing Fun!

Discussion in 'Electricians' Talk' started by sinewave, Jun 10, 2011.

  1. sinewave

    sinewave Screwfix Select

    Today's Scenario

    TNS supply in a Garage feeding an existing Non RCD fusebox.

    2 x New 2.5mm 3 core SWA supplies required for 2 new A/C units

    New 100A main switch fitted and then split tails in Henlies

    New Metal Clad 2way DB fitted with 63A 30mA RCD as a main switch and 2 x 10A Type B MCB's for the circuits

    Circ 1 radial was 26m, Circ 2 radial was 32m long, both terminated in to IP65 Rotary Iso's

    Brown core to L1, Blue core to L2 and CPC to Earth Connection

    Circ 1 Zs = 0.52
    Circ 2 Zs = 0.53

    Circ 1 RCD x 1 = 25.2ms, x 5 = 20.3ms, Ramp = 0.26mA

    Circ 2 RCD Tests fail all round, all connections good

    <strong style="font-size: 12pt; ">What went wrong?[/b]   
  2. proper spark

    proper spark Guest

    Is there something there that you have wrote that should give it away. Maybe im missing something. Ive read it 3 times and everything sounds good to me. Anymore clues what the fault is to do with;)
  3. J.P.

    J.P. New Member

    Just something which seems a bit strange Sine..surely a standard main switch feeding two RCBO's would have been better..not withstanding the fact that they would normally be type C's and probably more suitable for AC inrush..but down to the RCD failed tests which is the main thing..am working on it - don't bang the answer in yet M8.
  4. J.P.

    J.P. New Member

    Could you bang the failed number 2 RCD test results up Sine? and also IR readings for both cables..cheers M8.

    Also at what point in the circuits were the trip tests performed?..was it on the input side or output side of the rotary..and if on the output were the tests taken on the AC input terminals?..reason for asking is that on the dodgy circuit there could be a fault on the flexible from rotary to AC.
  5. J.P.

    J.P. New Member

    Mind you it could be a faulty RCD.
  6. sinewave

    sinewave Screwfix Select

    RCD tests conducted at incoming side of the Rotary Iso.

    Type B's are fine for modern Inverter A/C's JP, no inrush at all.

    IR's for all Circs = More Than!

  7. unphased

    unphased Screwfix Select

    tbh if the RCD incomer is protecting both circuits you don't need to test the RCD from both, just one will do. Must have left circuit 1 energised when testing RCD off  2?
  8. J.P.

    J.P. New Member

    Must admit Sine its a toughy (on line with good old Pengs questions of the day) the only thing left is the length differentials with respect to circuit legs which is irrelevant, and also it may be something to do with the metalclad DB?..what is it?..harmonics or something like that? I'm stumped tbqh.
  9. J.P.

    J.P. New Member

    No its good stuff Lucia..its getting on the lines of  ''question of the day'' which is no bad thing at all tbqh.
  10. cliffy b

    cliffy b New Member

    i give up pal, did you bend over and your pants split?
  11. J.P.

    J.P. New Member

    What is the answer Sine?..talk about being kept in suspenders.
  12. wally

    wally Screwfix Select

    Perhaps something silly like forgetting to turning iso switch on to circuit 2
  13. Moses

    Moses Member

    I dont think he knows what the answer is either !

    He's fishing!
  14. sinewave

    sinewave Screwfix Select

    Sorry lads, forgot all about this till today's morning cupa!

    Very simple really, the True Neutral core was in the earth connection in the rotary Iso and the True Earth was in L2!

    The question was written carefully to accurately show what was seen by the tester, on connecting the tester he could see Brown in L1, Blue in L2 and Green & Yella in the Earth as you'd expect so fired away with a Zs test and then RCD tests.

    What had happened was as 3 core SWA was used with a Brown Black & Grey core these had been taped up as per.

    First Iso was taped up correctly with the Grey taped Blue and Black as Earth, he got it wrong on the 2nd Iso for whatever reason but being as his taping is very thorough covering the whole length of the core you couldn't see that he'd got it wrong without unwrapping it.


    Just goes to show the importance of testing!

    The following statement was was drummed in to all DNO apprentices and I've never forgotten it.

    1) Never belive what your're told
    2) Never believe what you see
    3)ALWAYS test for your self!

  15. Lectrician

    Lectrician Screwfix Select

    Why an RCD?
  16. cliffy b

    cliffy b New Member

    4) never squeeze a 46" frame into a 44" pair of helly hansens
  17. sinewave

    sinewave Screwfix Select

    Twofold Lec, firstly manufacturer dictates it under the warranty scheme, secondly the outdoor also feeds the indoor unit in 4core which due to installation requires and RCD.

  18. Lectrician

    Lectrician Screwfix Select

    Not seen A/C manufacturers state RCD protection before TBH.
    Most A/C units would be in commercial premises usually, so RCD requirements could be circumvented in most instances, or compliances provided in different ways.
    RCD's just do not seem a good idea on A/C units IMO.
  19. pearcy

    pearcy New Member

    and there me thinking ya cheap tat tester had packed up ....simples  
  20. overnightsparks

    overnightsparks New Member

    Thought that would be picked up when doing the dead tests seems verry sloppy to only discover the reversal of a live conductor and cpc during an rcd test

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice