Disconnection times.....

Discussion in 'Electricians' Talk' started by barbaricduck, Oct 12, 2009.

  1. barbaricduck

    barbaricduck New Member

    Hi folks,

    Firstly I have just shelled out £45 for some GS38 test leads. A pair of leads; 1.2m long! £45! I reck the H&S police should go and duck off! Tvvats!


    Am a bit confused of dis times. I thought that for a typical domestic TN system the dis time is 0.4 if less than 32A cct. However, just been looking through a couple of PIR's from other sparx and they have listed lighting as 5s and power ccts as 0.4s..

    Is that correct? Regs seem to say otherwise.. Although imho it seems more sensible to have a higher amp cct with a quicker dis time..

    Anyone.... please... Thanx
  2. unphased

    unphased Screwfix Select

    Hi barabari

    In 17th edition for TN earth its 0.4s all circuits (0.2s for TT). The 5s disconnection time no longer applies; it is a remnant of 16th and earlier regs.
  3. lamps

    lamps New Member

    so a lighting ctt run in steel conduit with no bathroom lighting on it, is that not still a 5s time
  4. barbaricduck

    barbaricduck New Member

    Cheers Un..

    makes sense now - the PIR's are a couple of years old and to 16th.... Thanx
  5. unphased

    unphased Screwfix Select

    No lamps. Its 0.4s end of.
  6. lamps

    lamps New Member

  7. spark&half

    spark&half Active Member

    3.5.2 Disconnection times - TN circuits

    A disconnection time of not more than than 0.4 s is required for final circuits with a rating (In) not exceeding 32A

    A disconnection time of not more than 5 s is required for

    -final circuits exceeding 32a
    -distribution circuits..

  8. barbaricduck

    barbaricduck New Member

    Yeah spark and a 1/2, I concur!

    Sooo, a dedicated 9.5kW shower cct draws a possible/hypothetical 41A. This is permitted to take up to 5 seconds to disconnect. That sounds bad to me - surely with such a high load then ADS should be quicker. That is what it says in the regs though.

    Have dis times been altered from those found in 16th ed in line with 17th requirements for full RCD protection....?? ie Have the dis times been changed to reflect the extra protection offered by a RCD..

  9. Lokkars Daisy

    Lokkars Daisy New Member

    This is permitted to take up to 5 seconds to disconnect no cos it will require and rcd
  10. nselec

    nselec New Member

    Might be me being thick but surely if a cct is protected by a 30mA RCD (which the majority will be since 17th ed) then the disconnection time is not 0.4 seconds but 40mS at 1xIn which is in fact 0.04 seconds???
    So as far as a 40A shower, obviously in a room containing a bath or shower, then the disconnectin time is 0.04 secs not 5??
  11. 1ÿ Slave

    1ÿ Slave New Member

    RCDs should open in 200mS with a LEAKAGE current flowing equivalent to 100% of the rated trip current e.g. 30mA (OSG 11.4 ii)

    MCBs -
    Circuits not exceeding 32A : - BS7671 Table 41.1 TT 0.2S and TN 0.4S

    Circuits exceeding 32A - TN - 5s, TT - 1s (BS7671 411.3.2.3 & 4)

    This is fun isn't it!
  12. seneca2

    seneca2 New Member

    RCDs should open in 200mS
    300 ms for 61008.
  13. unphased

    unphased Screwfix Select

    Sorry for the bum steer. Didn't read 411.3.2.3. :)
  14. barbaricduck

    barbaricduck New Member

    Thanks all for responses.

    One thing tho; Lokkers the shower could be a cooker or something with similar consumption. So under 16th would not have necessarily required RCD. Again thanks good peeps..
  15. fabregas

    fabregas New Member

    Theres some duff information being offered up on this topic - Part p working Mr Mandleson

    My ****!
  16. clear as mud

    clear as mud New Member

    Part p has nothing to do with the amount of duff info, the duff info comes only from those who don't know the correct info. Prior to part P i suspect there were just as many of those.
  17. fabregas

    fabregas New Member

    Yes but since part p theres a lot more people purporting to know
  18. Removed 4

    Removed 4 New Member

    Does anyone know where I might buy an accurate stopwatch?

  19. mr sillys

    mr sillys New Member

    the canary islands are a good supply of rolex

  20. Removed 4

    Removed 4 New Member

    Did you say Rolex?


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