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  1. Weeloon

    Weeloon New EF Member

    Hi, I am resitting my FICA Underpinning Knowledge test next week and I stuck on a few questions in the mock tests they have on their website. I have been doing a lot of revision but my brain has gone to mush. Can anyone help with the following question?

    Question - The maximum earth fault loop impedance for a 16A BS 88-3 fuse system C for a 5s disconnection time with a U of 230V is

    A 5.08
    B 3.9
    C 3.2
    D 3.64

    They give you the answer but not how the answer is reached.

    Many thanks in advance for any help given.
  2. westward10

    westward10 In echoed steps I walk across an empty dream. Staff Member Moderator

    These are maximum values of Zs, where would you normally find these?
    There is no calculation required.
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  3. Sintra

    Sintra The Innkeeper Staff Member Admin

    Fig 3A1 in BS7671 shows that a 16A BS88-3 fuse system C takes 56A to disconnect in 5s. Then you can apply the formula given in appendix 3.

    Zs =Uo x Cmin / Ia
    Zs = 230 x 0.95 / 56
    Zs = 3.9 ohms
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  4. Weeloon

    Weeloon New EF Member

    Thank you for that, hope that is the last of brain fade for me.
  5. MFS Electrical

    MFS Electrical Forum Mentor

    Scotland, Inverclyde, Greenock
    Business Name:
    MFS Electrical
    Good luck with the FICA remember you get books to take in with you for all the questions. As long as you don’t do something daft on the install you should be good I shorted the motor starter to earth on the backbox :rolleyes: and still passed so don’t be too worried
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