3A fuses for extract fans

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

  1. JP.

    JP. Screwfix Select

    Must admit have never heard of fuses on both the perm and swl to fan - sounds rather insidious to me, and reminds me of the days of db's with n + l fusing..extremely dangerous tbqh..:D

  2. Lectrician

    Lectrician Screwfix Select

    Inrush is best dealt with with a C type, not increasing rating.

    Fans are commonly just tagged onto the lighting circuit with no protection, but for a couple years now fusing has been strongly encouraged to comply with manufacturer instructions, much the same way previously with showers and RCDs.

    How can you compare fusing both lives with fusing a neutral JP? That's just stupid! How to you see three phase boards and sw-fuses?
    FatHands likes this.
  3. seneca

    seneca Screwfix Select

    No JP, the problem is that IF the fan manufacturer stipulates that a 3 amp fuse should be incorporated in the supply that's what should be done. Our regs. state that manufacturers instructions must be followed. Imagine what would happen in the case of a fire for instance, investigators find that no fuse was provided so the installer could be held responsible! (very unlikely of course but I wouldn't want to risk it)
    FatHands likes this.
  4. FatHands

    FatHands Well-Known Member

    So to surmise (to get clear in my own head!): take a feed from the bathroom lighting to an FCU. Feed that to a triple pole isolator and feed the fan with that. Place the FCU and TP isolator next to one another on the outside above the bathroom door.
  5. Risteard

    Risteard Well-Known Member

    Regardless of whether a 6A or 10A BS EN 60898 circuit breaker is used or a 5A BS 3036 or BS 1361 / BS 88-3 fuse, or a 3A BS 1362 fuse none of these will provide any protection to the fan. The point is simply about adherence to manufacturers' instructions. But the sensible way to achieve 3A fuse protection is to fit an FCU with a 3A fuse in it, and supply the bathroom light from it, and then take the fan off the bathroom light. Then both permanent line and switched line are pointlessly fused.
  6. seneca

    seneca Screwfix Select

    Agreed, although not always practicable.
  7. Rulland

    Rulland Well-Known Member

    Tbh the FCU could be anywhere, but IMHO the isolator should be easily accessible for local and easy isolation, just my take though.
    FatHands likes this.
  8. stateit

    stateit Well-Known Member

    Generally by the light switch, by the door, so the fan can be turned off when you go for a pee in the night.

    That's where I put them,and that's what I tell my customers why I've put them there.
    FatHands likes this.
  9. JP.

    JP. Screwfix Select

    Thanks guys. I will check up on what fusing is required by my Manrose inline fan - if it does say 3 Amps then I will knock my dedicated supply to bathroom down to 3 Amps - I can put an FCU below my DB (not yet fitted) - all good stuff lads tbqh.
  10. seneca

    seneca Screwfix Select

    I've been using Greenwood Airvac fans for a while now, they don't specify a 3 amp fuse.
  11. unphased

    unphased Screwfix Select

    Greenwood Airvac, eh! Nice. :)
  12. Lectrician

    Lectrician Screwfix Select

    JP, if you're going to put an FCU below the board, consider an MCB instead. Some makes do manufacturer odd sizes, and as you haven't chosen a make...
  13. Coloumb

    Coloumb Well-Known Member

    So guys - the motor gets jammed and draws more than 3 amps but less than 6? Correct?
  14. unphased

    unphased Screwfix Select

    Hi Ben

    I think the 3A fuse might just about discriminate with a 6A mcb, if the overload generated by a stuck rotor is pulling overload current. The 3A is more likely to blow and release the load than the 6A. I expect a stuck fan due to the blades jamming is going to get hot and potentially busrst in to flames. Whether this has any substance, I don't know, just my own thoughts. 3A could probably suffer 6A for a short time whereas a 6A would probably hold up to 10A?
  15. Lectrician

    Lectrician Screwfix Select

    They should be sticking in thermisters for that really.

    In a sheltered housing scheme we do maintenance on, a fan in a bathroom ceiling caught fire (well, smoked the loft out). Since then, the estates manager has instructed yearly cleaning to be done, and MWC issued for each fan cleaned!
    FatHands likes this.
  16. seneca

    seneca Screwfix Select

    As I said earlier in this thread Lec I couldn't believe the state of a small kitchen fan I came across recently, so much heat had been developed that the plastic housing was almost unrecognisable, just lucky that the windings went o/c before the flames started! I think it's made me take the 3 amp fuse a little more seriously now. This one had been wired into the back of a ring socket btw.
  17. Phil the Paver

    Phil the Paver Screwfix Select

    totally un related, but on my motorbike the alarm has a 1A fuse, anyhow the other day it started playing up, so I cut the imobolisor wires out of the loom so the bike would run, this still left the alarm working as a siren and flashing LED.
    Yesterday I had a look at it to see what went wrong, upon removing it from the bike I could smell it had burning on it, I opened it up, only screwed together, well inside I was shocked to find melted plastic, wires welded together causing a short, but a fuse that still hadn't blown??? 12 volts 1 amp buts lots of damage, needless to say it's all in the bin now. :p:p
    Jitender likes this.
  18. Risteard

    Risteard Well-Known Member

    It definitely won't.
  19. unphased

    unphased Screwfix Select

    Not in a dead short or fault to earth, no. But in an overload it would. That's why it is specified by the manufacturers.
  20. Risteard

    Risteard Well-Known Member

    You sure about that?

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