3A fuses for extract fans

Discussion in 'Electricians' Talk' started by unphased, Jun 19, 2014.

  1. unphased

    unphased Screwfix Select

    Is it just the permanent live that needs it on a timer fan?
  2. wally

    wally Screwfix Select

    Dont understand un, Not all fans need a 3 a fuse, some makers say the 6a MCB is adequate.
  3. seneca

    seneca Screwfix Select

    I've always assumed it's both feeds that need the 3a fuse UP. Recently I've been using the fans that don't require it though.
  4. Jitender Gangar

    Jitender Gangar Active Member

    If i use a timer fan, which requires a switched and permanent live I usually wire into the lighting circuit incorporating a fan isolator switch (3 pole switch).
  5. Cheburashka

    Cheburashka Active Member

    If you have the FCU on the supply to the bathroom lighting it will cover both the permanent and switched lived.
  6. seneca

    seneca Screwfix Select

    Yes I sometimes do it that way but depending on existing wiring not always easy is it!
  7. Cheburashka

    Cheburashka Active Member

    Very true Senaca. I have often wondered about the requirement for a 3Amp fuse myself as a permanently wired fan is a fixed load so it should be treated as such.
  8. seneca

    seneca Screwfix Select

    True it's a fixed load so overload protection isn't required but they're concerned about a fault condition, eg stalled rotor, or shorted turns etc. causing excessive heat. I changed a kitchen fan recently and I must admit I would never have thought it possible for a such small motor to have produced so much heat and melted the plastic housing that it was in!
  9. Rulland

    Rulland Active Member

    Regardless of wether a fan isolator is used, if the manufacturers data states a 3A fuse is required, then a fan isolator off the lighting circuit does not meet the criteria specified.
  10. seneca

    seneca Screwfix Select

    Agreed Rulland, a 3 amp fuse is an entirely different issue to a fan isolator, very often both are required. I'm surprised no one makes a 3 pole isolator with 2 fuse holders incorporated.
  11. stateit

    stateit Member

    Scolmore make one in their Click range.

    It only has one fuse, but you place it next to the light switch in a dual box & it serves as an FCU as well...

    http://www.scolmore.com/article.php?id=51&headline=Protection_for_Ventilation_Equipment
    FatHands likes this.
  12. Rulland

    Rulland Active Member

    Now there's a good idea, How long has such a thing been out?, As I've never seen one before, But to be fair I haven't really looked tbh.
  13. unphased

    unphased Screwfix Select

    I was puzzling over this for ages. I am still unsure. My thoughts are that the permanent live on the fan is permanently feeding the fan even when the timer function has expired. I have tried to keep the L and SL on the 3A fuse and I always put a tp isolator in anyway. But today I have put the permanent feed only on the 3A fuse and taken the SL and N from the light fitting. It sits okay with me. What do you guys reckon?
  14. Risteard

    Risteard Member

    I think it's rather pointless fusing only one of the line conductors instead of both (notwithstanding the fact that this is also pointless).
  15. seneca

    seneca Screwfix Select

    Not too sure about that UP, after all it's the motor that could possibly seize up and overheat so i'd say that's the bit that needs the fuse, rather than the electronic parts on the permanent feed?
  16. Lectrician

    Lectrician Screwfix Select

    You can get fused three pole isolators these days. I am yet to look at one to see if it fuses both. The NIC are hot on fusing fans. (manufacturer instructions).

    Also, if you take a fan feed from an FCU on a ring, instead of the lights (for example in a utility), you need to wire it in 1.5mm minimum, not 1.0mm.
    FatHands likes this.
  17. unphased

    unphased Screwfix Select

    Yes I remember reading about that minimum 1.5mm2 cable size somewhere. I can't recall ever wiring a fan off a socket circuit, though, always use lighting circuit. If you remove the permanent live from the fan does it not make it inoperable anyway? I seem to recall you have to link the L and SL in the fan if you want to make it in to a straight on/off without timer function. So, if the 3A fuse failed in the line, the fan would stop.
  18. seneca

    seneca Screwfix Select

    Yes, that's since the "1.00mm to be used for lighting circuits only" change to the regs. Lec.
  19. Lectrician

    Lectrician Screwfix Select

    Yea, changed in the green book. Many people don't realise though. Smokes, cent heat etc.

    You need to fuse both L and SL IMO. interested to see one of these fused TP iso's though, it appears they only fuse the perm live.
  20. JP.

    JP. Screwfix Select

    Its fine running the fan off the lighting circuit as long as the mcb is 6 Amps and lets face facts this is standard practice. Hover sometimes inrush probs due to florries etc are overcome by the fitting of a 10 Amp mcb in place of the 6 amper - this effectively negates the fan guarantee, and can cause the fan to go into ''Catherine Wheel Mode''..:D

Share This Page