FICA multiple choice help

[Weeloon]

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.

 

[westward10]

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

 

[Sintra]

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

 

[Weeloon]

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

 

[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 and still passed so don’t be too worried