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  1. hsuelec77

    hsuelec77 Active EF Member

    Hi all,

    Completed my first pir yesterday :) now this client has got a three phase supply, TNS which feeds a ground floor shop and a flat above, the flat has a on peak and off peak supply. With the tails for the flat going into two kmf switches with a sub main cable of only csa of 10mm T+E for each supply protected by a bs1361 60A with a cable length of 6-8 mtrs max.
    Q1 on my supply characteristics where it says main switch/circuirt breaker do i enter the details of the kmf switch ?
    Q2 If the flat has the main protective bonding conductors going to the db with a earthing conductor as 4mm off the T+E this has to be upgraded? What would you code it?
    Q3 Would you code old and worn pendants etc?
    Q4Special locations with no IP rated luminaires?
    By the way is there any courses on form filling because i haven't had much experience was mainly installing, didn't fancy doing pirs but on the flip side you can get remedial works.

    kind regards
  2. spinlondon

    spinlondon Trusted Advisor

    Harlow Essex
    Q1 Yes.
    Q2 If the conductor does not satisfy the adiabatic equation code 1, if it does satisfy the adiabatic equation, code 2.
    Q3 Only if they present a danger, or are likely to in the near future (i.e. before the date of the next inspection).
    Q4 All electrical equipment is IP rated, (excepting uninsulated conductors), even if the rating is not indicated on the equipment.
    What is the rating of the luminaires, and what is the minimum required for the location?

    I'm not aware of any courses.
    Last edited: Oct 20, 2011
  3. hsuelec77

    hsuelec77 Active EF Member

    Battern holders witin zone 1 and 2, i knew you was going to say adiabatic equation but when i did my 2391 this year and passed i was told forget that equation its got to be min 16mm, so really regardless of the result when carrying out this equation the installtion would require to be unsatisfactory. Im using amtech software, is ther a bs number for kmf switch because there's nothing within the list it gives me.

    Thanks spinlondon
  4. spinlondon

    spinlondon Trusted Advisor

    Harlow Essex
    Zones 1 and 2, require a minimum IP rating of IPX4. I take it that they are below 2.25m from ffl?
    Minimum of 16mm, or minimum of 6mm?
    Actually, I've just noticed that you said the installation is TN-S, which would mean that if the adiabatic equation is satisfied, a code 4.
    I believe the BS number is BS EN 60947-3.

    p.s. I've never actually taken the 2391 exam, but if I were to and was informed in the course to forget the adiabatic equation when sizing earthing conductors, I'd have a few words to say to the tutor.
    There are times when sizing an earthing conductor as per the requirements of Tables 54.7 and 54.8 would produce a CSA that would not satisfy the adiabatic equation, and the conductors would fail in the event of an earth fault.
    I've seen such a situation with underground sub mains, which cost an awful lot of money to replace.
    Last edited: Oct 20, 2011
  5. hsuelec77

    hsuelec77 Active EF Member

    I've worked out that 4mm cpc would be sufficent can you double check mate,

    ZE+R1+R2=0.19, T=0.1, K=115




    SQROOT 146652.1=383


    4MM Is greater in the T+E so ok, why would you code it 4 doesn't this comply to bs7671, that bsen 60947-3 is for double pole main switch which are sited on dbs im sure? Also doesn't it matter that the main protective conductors to the flat are in the earth terminal in the db and not at the m.e.t?

    thanks again fella
  6. spinlondon

    spinlondon Trusted Advisor

    Harlow Essex
    Your adiabatic equation calculations look fine to me.
    I said code 4, because I thought the CPC was also a bonding conductor.
    From re-reading your OP, I'm not so sure it is now.
    If the CPC is not acting as a bonding conductor, then no code.
    If it is acting as a bonding conductor (i.e. the services are bonded in the flat, to the flat CU, and the only earth conductor from there to the MET downstairs is the T&E CPC), then it is under sized, and should be 6mm².
  7. i=p/u

    i=p/u Trusted Advisor

    nice sumssssssss
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