Bathroom fan installation - quick FCU query

Discussion in 'Electricians' Talk' started by JimmyNorwich, Feb 12, 2018.

  1. JimmyNorwich

    JimmyNorwich New Member


    I've had a chat with a spark who popped round to take a look at the wiring for an inline extractor fan in my bathroom. I've run the wires but haven't connected anything up. He'll be back to do that and check things over.

    He said that there's no need for the FCU that I'd bought: The reason that I bought it was because I thought that in order to comply with Part P you needed to have the fan protected by a fuse as specified by the fan manufacturer. The instructions say 3A. The lighting circuit is 6A. Have I misunderstood the regs?

    If indeed I do need an FCU, would it simply be inserted as per the red text/arrow in the attached diagram? My fan is actually a timed fan so I appreciate it'd be 3-core rather than 2-core and earth as per the diagram (it was the closest I could find that I could easily edit).



  2. JP.

    JP. Screwfix Select

    No you cannot connect it there Jimmy - the Sparky's will elucidate further m8
  3. JimmyNorwich

    JimmyNorwich New Member

    Thanks, JP. Just been thinking about it a little more. The FCU can't sit there on account of it only accommodating 2-core and earth wire. I'm not aware of an FCU that'll take care of 3-core and earth either. Would it be best to separate off the existing 2 lights and switch that I have and put the FCU before these? To reiterate, I'm not doing this work. Just like to understand these things.

  4. JP.

    JP. Screwfix Select

    Jim the sparks will clock your post m8 and advise accordingly
  5. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    Putting a 3A fuse in line to that fan seems daft, guessing a 6A type B breaker upstream is protecting the circuit, there would not be any discrimination between that and that 3A 1362 sat in the FCU carrier.

    I have never put a fuse in to protect the wiring for a 15 quid fan, its a fixed load and never going to draw much current and what would happen if say I got found out and I did not follow the manufacturer's stern instructions. . .. .Nothing thats what.

  6. JimmyNorwich

    JimmyNorwich New Member

    Thanks @sparky Si-Fi - that does seem to be the standard approach from what I read online. I just wanted to make sure that the work was up to standard (whatever that really means). I'll chat to the spark and mention my concerns. I suspect he'll say exactly what you have.


  7. Bob Rathbone

    Bob Rathbone Well-Known Member

    The fuse does not protect the fan, it protects the wiring to the fan and in this case all of the lighting circuit.
  8. sparky Si-Fi

    sparky Si-Fi Well-Known Member

    That 3A fuse is protecting the flimsy flex in the fan housing and to be fair as said, thats a fixed load its not going to draw hardly anything on full chat, if any issue arises inside that fan, the electronics will go pop long before that fuse
  9. Dr Bodgit

    Dr Bodgit Well-Known Member

    If you want to protect the fan wiring with a 3A FCU or whatever, you could put a cheaper 2 pole FCU on the live/neutral feed to the lighting, saves the expensive of having a 3 pole switch just for the fan. My entire bathroom (5 spots, power for mirror and extractor fan) are done this way, single DP FCU with 3A fuse serving the lot. Just makes sure its "accessible".
  10. Bazza

    Bazza Well-Known Member

    As above. There is no point in a 3amp fuse after a 6amp MCB. The MCB will always go first.
    Does nobody ever look at protective device discrimination tables??

    My guess is the only reason to have a 3amp FCU before a fan is the very rare occasions when it is powered from a ring final.

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