Fusing an Extractor Fan

[eyedee]

I'm fitting new lights and fans to my bathroom and I've come across a few questions I'd really appreciate help in having answered. Can I also say I'm not an electrician but I am having the wiring looked at as required to check the safety and regs-compliance etc. but I am intent on doing the work myself. I really enjoy learning new skills and understanding things better!

Basically, I am installing a wall fan with timer module, a shower fan with timer, 3 x 50W 240v Halogens and 1 x 12v Halogen with it's own transformer (due to the 12v halogen and the shower fan being a single unit - although the fan is powered seperately of course). I've installed plenty of lights in the past so no questions there, but the fans are new to me.

I learnt about how fans with timer modules have Neutral, Permanent Live and Switched Live and that's all fine too, but I am a little confused when it comes to installing a 3amp fused spur on each of the extractor fans. Both fans instruction manuals point out that these are required. I have been to a number of DIY outlets looking for a 3amp fused spur but only found 13amp fused spurs available - I'm guessing this is really simple, but I'd rather be sure I'm not doing it wrong - so is it just a simple case of swapping the 13amp fuse out for a 3amp fuse? Secondly, I initially assumed that both the Permanent Live and the Switched Live should be fused, but the fans instructions only shows the Permanent Live being fused. How is that wired up inside the Fused Spur Box? The Fused Spur provides terminals for Live, Neutral and Earth, but in this case there is no Earth, so is it a case of wiring the Permanent Live into Live, the Neutral into Neutral, ignoring the Earth and using a Connector Block to continue the Switched Live to the fan?

Oh, and one last question (probably daft, but I'm really curious)... I plan to purchase two fused spurs, one for each fan, but is it legally possible and safe to wire the two fans into one 3amp fused spur?

Sorry for the long post and thanks for taking the time to read this and provide your advice.

 

[holmslaw]

..

 

[Chri5]

Where would you site the 3a fused spurs ?

Do you understand bathroom zones and the meaning of Part P / notifiable works ?

As the wiring for fans will be via the light circuit the current best practice is for a fan isolator, however if the bathroom has natural light (as in a window) there is no need to provide either an isolator or fused spurs.

The isolator or fused spurs allows isolation of the fan(s) for mtce locally, but since you may have natural daylight turning the lighting circuit off at the main board (CU) is acceptable.

 

[eyedee]

Sorry, I should have said, the fans are to be on one switch and the lights are on another - there will be two pull cords in the bathroom. This is an already tried, tested and preferred method for our family.

I understand the basics of bathroom zones and all lights and fans comply with regulations. The shower fan is actually in the loft, the wall fan is zone compliant, the lights are bathroom and shower specific and zone compliant. If notifiable works is the requirement for paperwork to be provided by a qualified electrician certifying the work as being safe and passing regulations then I get that too. Otherwise I'm not sure.

I thought it would be easiest if I drew up a quick wiring plan for the bathroom electrics. This is the method that I have been advised to follow by a qualified electrician, but with a couple of additions that he didn't know about (and nor did I when we initially discussed what I was having done). I hope this gives a clear idea of my wiring intentions.

Untitled

• eyedee
• 17 Aug 2009
• 3

 

[rebuke]

If notifiable works is the requirement for paperwork to be provided by a qualified electrician certifying the work as being safe and passing regulations then I get that too. Otherwise I'm not sure.

If you do the work yourself, you need to notify your LABC (Local Authority Building Control) before doing the work. This will normally involve a fee of ~£100 - £200 depending on the LABC. They will then come out and inspect and test the work you do, and if they're happy with it, provide a building control completion certificate. See the wiki for more info.

Proper electricians will generally become a member of a self certification scheme, which means they can self certify their own work, rather than have to have the LABC out every time. Officially, they are not allowed to certify someone else's work, although there are some that do - remember though, this is illegal.

Most sparks will be happy for the householder to do the donkey work of chasing out walls, digging trenches etc, but I'm guessing in your case since the vast majority of the wiring is presumably in a loft space, there isn't much of that to do - for two fans you may find it cheaper to get a spark in to do it, than paying the LABCs fees...

 

[eyedee]

Thanks for the heads up rebuke. Pretty pointless doing relatively small jobs yourself then. I've already striped the bathroom to a bare shell and rebuilt it so I have already done the hard graft including siting the fans and channeling the wall etc. I've also already cut the holes ready to accept the new down lights, bought the lights, firehoods and fans so it's now just a case of installing it and wiring it all up. I'm sure it would be cheaper just to get a sparks in for a day rather than go through the LABC channels.

I'm still very interested in knowing if my wiring diagram is any good though and if it would be safe and pass regs etc. I'll no doubt chat with the electrician about it when he arrives, but I'd still be interested to know what experienced members here think of it.

 

[rebuke]

I can't get it big enough to see clearly what all the wires are, but are you trying to use FCUs to fuse down both the permanent and switched live in some way, as they only fuse one of the poles, so that won't work (and if you don't fuse down one of them then it's pointless having the fuse in the first place).

For the set up you want, I'd probably not bother with an FCU, since the whole circuit is presumably breakered at 6A, but anyway, if we must follow the manufacturers instructions then I'd take a feed off the lighting circuit, put it through one FCU, then take that in to a junction box where i run the cable to the switch etc. Then I'd have a 3-pole fan isolator (switches perm live, switch live and neutral) before the fans (one for both is probably fine).

 

[ericmark]

Part P has been covered so I will just comment on work.

There seems to be a major problem with manufactures stipulating 3A fuses and on previous posts different replies have been received from the manufactures as to why they ask for them. I would guess it was dependent on who answered to phone.

So the reason could be:-

1) So the 3A fuse will open before the supply to lights so any fault on the fan will not stop lights from working. This is unlikely as a 6A B type MCB is likely to trip before a 3A fuse.
2) To protect the fan should it jam etc. This is also unlikely as in most cases the fan would burn out before the fuse would blow.
3) Because 3A is the recommended fuse size by IET for all small appliances where two fuse sizes 3A and 13A are considered ample to cover all cable sizes and any appliance protection should be included within the appliance. This seems the most likely reason for stipulating a 3A fuse.

If 3) is correct then for a fan connected to a lighting circuit supplied with a B6 MCB then an extra fuse is not really required. However a means to isolate the fan is so some lockable switch is required. The standard fan switch does normally come with a device to take a lock but they are often lost. The FCU has provision for a lock to be placed in the open fuse carrier so is a very good way to provide isolation.

The fans take well under 1A so running two from same supply is not really a problem and this also means if the fuse was to protect the fan then more likely a 1A would be recommended.

Each electrician has to decide himself what he thinks the reason is for the 3A fuse and some will consider it is only required when supplied from the power i.e. 32A ring main and others will want it even when supplied from the 6A lighting circuit and as the person signing the paper work that is their job to choose. Either way it will also need protecting with an RCD and comply with all the regulations.

To do any work therefore you need to find someone to sign it off first either LABC or Electrician willing to call the work his. And follow their instructions. Only by fitting to highest possible standards can you ensure it will pass if you have not questioned them as to what the expect first.

With LABC charges so high it is not economically viable to DIY in a bathroom and although you may take pride is your DIY I would think it is a lot of money to be able to DIY and may be you could better use you DIY skills else where.

 

[eyedee]

Thanks for your helpful info and advice. I'm sure that I'm going to get a sparks in to complete the job anyway as I will be selling up some time soon and I wouldn't want any issues when any inspections are done etc. But that is all really interesting. In fact I am becoming so interested in electrics that I am starting to wonder if I should take it up as a career. My present job doesn't do it for me anymore and I've been thinking about other opportunities for a few weeks.

Sorry, back to the topic though, I was under the impression that it was not necessary to install a 3 pole isolator switch, but that it was only advisable? My old house had, and my parents place has, a fan in the bathroom that is wired directly into the lighting circuit without any fuses, rcd's or isolators!

rebuke, I was thinking exactly what you have said about the single pole being fused. The instructions for both fans show only the permanent live being fused, but what good is that when there are three poles?

And thanks for your insight ericmark, that's real food for thought.

 

[flameport]

Two fans extracting from the same room is not a good idea.
They won't work properly, since one will inevitably be more powerful than the other.
Either just fit one of them, or if that one is not big enough, get a more powerful fan.

 

[rebuke]

If you fuse the permanent live before the switch, then the switched live will also be protected - I suspect that's what the diagrams showed. If not, then it could be that due to the way it's wired, the switched live is only 'sensed' in some way, and it can't actually provide power to the fan, but I wouldn't rely on that...

A 3 pole isolator is not absolutely necessary, but they are useful for a number of reasons:
* If your fan breaks for any reason, you can isolate it and therefore keep the lights on
* You can do maintenance (cleaning) on the fan without having to turn off the lighting circuit (if you've got a window in the bathroom though this point is negated somewhat).
* If it's late at night, you want to go to the bathroom but don't want the fan coming on waking everybody up you can isolate it before turning the lights on (this one isn't relevant in your case though, since you've got the fan individually switched).

 

[ban-all-sheds]

A switched FCU would also act as a perfectly good isolator for the fan(s).

 

[eyedee]

The room is split into two areas, one being an enclosed shower unit - hence the use of two fans. Even if one were to be less effective, it would still be a more effective method of removing steam from the shower enclosure than leaving the door open and allowing the main fan, which is sited across the other side of the room, to remove all the steam and condensation.

I see what you're saying rebuke. I've put another pic up, I only hope it's slightly more legible. One of the instruction manuals have the fuse after the switch, one is before. I think the one that shows the fuse being after the switch has simply made a mistake.

As ban-all-sheds says, the switched fcu would work as an isolator too.

Untitled

• eyedee
• 17 Aug 2009
• 2