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disconnection

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  1. rustynails

    2392 Question: Maximum earth loop impedance for 20A BS88 (gG) fuse

    What is the maximum earth loop impedance to BS7671:2008 for a circuit protected by a 20A BS88 (gG) fuse giving a 5 second disconnection time is: A: 7.42 B: 2.91 C: 1.84 D: 1.35 The green book says the ln for this type of fuse is 78A p299, that doesnt give you the right answer though. :confused5:
  2. S

    disconnection times and RCD

    On the 2391 training course for all of this week and something popped up that I would like to what other people made of it. So we are talking disconnection times, and the question of RCD's pop up. More to the point, circuits not meeting the required disconnection times. I thought I would use...
  3. C

    s type rcd

    Hi all, looking some advice on s type rcds. Basically can you use them on tt installations for earth fault protection on circuits that don't require additional protection? Know that on a tt installation disconnection times of either 0.2 sec or 1sec must be achieved depending on circuit, but with...
  4. N

    RCD tripping times, 0.4 or <200 etc.....

    I always been told that an 30m/A RCD should trip within 200m/s (x1) and 40m/s (x5). But something iv never taken much notice of before is on test sheet the maximum disconnection time of a circuit less than 32A is 0.4. So....which is it? within 0.4 or within 200m/s????
  5. R

    max allowable disconnection times?

    hi guys, what is the max allowable disconnection time times under fault conditions for kitchen lighting, bedroom socket outlets and also for a shower? thanks in advnace i appreciate all your help
  6. S

    Disconnection time of external bulk head...

    i need your help please this question is going to be a long 1... first let me explain the situation... Electrical Supply The electrical supply to the house is 230V, 50Hz, single phase and together with the installation forms part of a TN-C-S system. The electrical intake position is housed in...
  7. ringer

    Supplier's fuse, disconnection time and max Ze

    Have a job where Ze is 0.36 ohms on a TNC-S with 80A BS1361 suppliers fuse. The general rule, as per OSG (page 11), is if Ze is below 0.35 ohms then this is acceptable, but that relates to a 100A fuse (OSG fig 2.1 on page 15 refers). Now I believe that this installation should comply, so have...
  8. E

    cooker disconnection reconnection

    Hi guys. In a week or so I have a oven thats in need of a new cupboard/unit that houses it. The plan is to isolate securely, disconnect, inspect/test the supply, and assuming all goes well to this point, fit the new cupboard/unit and then refit and reconnect the oven, MWC. Everything is going...
  9. La Poste

    5 second disconnection time

    Just a quickie to refresh my memory. TN system disconnection times. Final circuits not exceeding 32 Amps. 230V 0.4 seconds. (table 41.1 page 46 BRB) Final circuits exceeding 32 Amps IE fixed equipment and distribution circuits. 230V 5 seconds. RCD's are used for socket outlets not exceeding...
  10. D

    Disconnection time with a PV sytem installed.

    Hello all. Could any experienced sparkies please please explain to me how RCD tripping times can be adhered to when a PV sytem is integrated into a domestic consumer unit if the inverter takes up to 5 seconds to isolate the AC outputwhich it feed to the domestic supply at the consumer unit. Fed...
  11. W

    TT Max ZS loop reading for circuits over 32A

    HI all anyone know the above, i put 1667 ohms in the box normally for all TT circuits but noticed the other day it is only for circuits upto 32A Anyone enlighten me, i need it for a 50A and 40A circuit?? thanks
  12. cashnotakite

    "just bang it on an RCBO!"......... TABLE 41.3

    this slightly confuses me; whenever a Zs reading comes up too high, e.g on a particularly long run, to get around the problem if you cant change the MCB rating, I get told to change it for an RCBO. Table 41.3 of the regs gives max Zs values for both MCB and RCBO protection. If our Zs value...
  13. S

    PIR on property with disconnected supply

    Hi folks, client has requested PIR on a property with disconnected supply (not sure how disconnection has been effected). Property has been empty for a long time and potential buyer (retired electrician - no pressure) wants to know as much as possible to see if price can be negotiated down...
  14. R

    disconnection times

    Circuits under 32A the disconntion times would be 0.4 and anything over woud be 5 am i right.
  15. C

    Disconnection time for distribution circuit

    I'm looking at remedials from a PIR and one thing is a switch fuse with an 80 amp BS88 is serving a 16mm run of 2 core and armour SWA which serves 3 sub boards in 3 seperate outbuildings and they have been wired so they loop in and out at henley blocks until the final sub board. The total run is...
  16. D

    Disconnection times

    Hi all, can someone tell me what the disconnection time is for circuits supplied from a distribution circuit?
  17. La Poste

    Disconnection times

    This might help a few of us suffering the 2391 exam. Maximum disconnection times for a nominal rms line voltage to earth, U0 of 230V Firstly for a TN system: Final circuits not exceeding 32A = 0.4s Final circuits exceeding 32A = 5s Distribution circuits = 5s For a TT system Final circuits...
  18. J

    r.c.d. disconnection times.for a m.k. consumer unit.

    hi there does anyone knowthe tripping times for a m.k.sentry 63 amp/2 pole/30mA r.c.d.device,it is part of a 8 way m.k.consumer unit,i am not sure if this device as a time delay incorparated,the number on the front of it is say's m.k.sentry /63 amp/5760s,your help would be appreicated,cheers...
  19. silver surfer

    disconnection times v voltage bands

    Guys BS 7671 table 41.1 shows that a disconnection time of 0.4 secs for 120<volts to <inc 230 volts, and a disconnection time of 0.2 at 230< to < inc 400v. (TN systems). My query is with a 10%+/- tolerance which could possibly increase 230 volts to 253 volts hence taking your 230v 0.4s disc...
  20. V

    Disconnection times for 30mA RCD at 5 times current.

    Hi guys ths is my first time on here and relatively new to electrics. I was asked to find the times of disconnection needed for 5x and 1x. I was wondeering if anyone could give me a push in the right direction by pointing out where i could find such useful info inthe BS 7671 or onsite guide...

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