Disconnection times

Discussion in 'Electricians' Talk' started by Alan sherriff, Jan 12, 2018 at 9:09 AM.

  1. Alan sherriff

    Alan sherriff Member

    Currys came to fit a cooker and refused as earth loop to high 1.37 ohms, on 32amp type B c/b with 6 mill t/e on the 2008 times comes out at 1.44 ohms. New amendment 3 including 80% rule 1.1 Ohms as old install do I still use old times or work with new times
     
  2. Coloumb

    Coloumb Well-Known Member

    I don't get what you mean, did you put in the ctt or your just replacing the oven on an existing ctt? Which has a Zs of 1.37?
     
  3. seneca

    seneca Screwfix Select

    Is there a 30m/a rcd in circuit? If so there's no problem. I get this quite often in my area as there's quite a lot of TT installations about and people from places like Curry's etc. don't understand it when they get a loop test figure of 80-100 ohms !
     
  4. unphased

    unphased Screwfix Select

    Its a standing joke with me how people who come to install appliances refuse to do so on so many spurious grounds. I would just get a refund for the fitting charge from Currys and do it yourself. There is nothing unsafe about a high Zs, as Seneca has explained. The refusal to do it is more a "we can't be bothered because we are lazy sods" than a true reason. The problem in society is the mention of Health and Safety. When you challenge Curry's thats what they will say, even though they are clueless as to why they have refused that's what they will hang their decision on. Its all so daft.
     
  5. unphased

    unphased Screwfix Select

    There is also a great deal of confusion in your post, Alan. 80% rule of thumb is just used as a quick assessment on site as to whether the circuit is going to be in tolerance. Far more is made of it than is necessary, usually by the intellectually challenged. (Not you!) As you point out the maximum Zs is the the one to use. There are far too many people spouting rules and requirements about and misleading each other with misinformation. I wish Currys would just leave it to people who know their job and stop interfering with their "I thought this and I thought that" meddling. Currys do this regularly and as I said for spurious reasons mostly.
     
  6. Lectrician

    Lectrician Screwfix Select

    The 80% rule is in place as the tabulated maximums are based on cables running at 70deg. Temperature affects the resistance, and therefore the disconnection time. The 80% rule of thumb is used as when testing, the cable will not be at operating temperature. In practice, the cable will never be running at 70deg! Even without the 80% your reading is bang on the money - It is a higher reading than you would expect for a cooker circuit from the origin of supply. I would be interested to see it retested. I reckon they tested using a plug in lead which often can give higher than expected readings, particularly with Fluke meters.

    For info, the old EFLI values were based on a voltage of 230v. They are now based on 218.5v (5% of 230v, our maximum permissible volt drop). Oddly, no account is made for the supply voltage tolerance.

    A B type MCB will trip "instantaneously" at 5x its rating, a C type at 10x, and a D type at 20x.

    32 x 5 = 160. 218.5/160 = 1.37ohm. 80% of this is 1.14ohm.
    32 x 5 = 160. 230/160 = 1.44ohm. 80% of this is 1.2ohm.
     
  7. Risteard

    Risteard Well-Known Member

    Actually, the 95% is precisely to allow variation in the incoming voltage due to legal tolerances. They felt that they full 6% was unduly pessimistic, but it still was the reason for that change to the Regulations.
     
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  8. leesparkykent

    leesparkykent Well-Known Member

    Are you for real? You have written that there is nothing unsafe about a high Zs!....maybe not in the OP's case but you are clearly a fool if you genuinely believe what you've said.
     
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  9. Coloumb

    Coloumb Well-Known Member

    He means when an rcd is used as Seneca has stated. Then it’s fine. Un isn’t suggesting otherwise.
     
  10. leesparkykent

    leesparkykent Well-Known Member

    Cheers Coloumb...next time I'll tag you in to the post. I didn't realise that he now speaks through you ;)
     
  11. Alan sherriff

    Alan sherriff Member

    I was looking at protection via the disconnection times prior to Amendment 3 and what they are now is not giving me a .4 second dis time.If installation was tested to an installation prior to amendment 3 and passed and now failed due to lower resistance values
    As for supplementary protection via RCD I did not mention that clause for complying as RCD can fail
     
  12. Bazza-spark

    Bazza-spark Well-Known Member

    I think if you read the post it is clear his reference is to Seneca's comment about an RCD.

    Kind regards
     
  13. unphased

    unphased Screwfix Select

    For the benefit of Lee not a sparky in Kent. EFLI is important where there is no 30mA RCD protection on the circuit. Where there is an earth fault on a TN system and only an mcb or rewireable fuse is protecting the circuit, there is a risk that the circuit would not disconnect in the required time if the maximum allowed Zs exceeded the values tabulated in BS7671. Seneca Coloumb, and Lectrician understand that, but it is way over your intellect. You antagonistic little sh!t.
     
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  14. leesparkykent

    leesparkykent Well-Known Member

    ;)
     
  15. leesparkykent

    leesparkykent Well-Known Member

    I know his puppet has just said the same thing. Kind Regards
     
  16. unphased

    unphased Screwfix Select

    I would question why Currys get involved in 'testing' a circuit, anyway. Their job is to turn up, connect the appliance and go home. They are not qualified to decide whether a circuit is safe. They should either stop offering to install appliances for people or employ a qualified sparky to test the circuit beforehand.
     
  17. Bazza-spark

    Bazza-spark Well-Known Member

    Takes a little longer to reach the spirit world. :D:D:D:D
     
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  18. leesparkykent

    leesparkykent Well-Known Member

    lol, I'm glad your still here though Bazza-spark...I knew it was BS.
     
  19. Bazza-spark

    Bazza-spark Well-Known Member

    KIAB and leesparkykent like this.
  20. unphased

    unphased Screwfix Select

    Lee. You are just a forum troll who loves to winde people up. Face it, you are no match for me so just carry on 'liking' posts that add to your sick mind and keep having your fun with me. :D BEng. Lol. Apprentice trained gimp.
     
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