Author Topic: UK toilet extractor fan  (Read 5494 times)

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Offline MajorbobTopic starter

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UK toilet extractor fan
« on: August 17, 2021, 05:48:44 pm »
Hi All,

I'm bricking up a window and installing a timed extractor fan in my downstairs toilet.  This room is just a toilet, no basin or anything else.  The only power it will have is a 6A lighting circuit and it is very lightly loaded.  It's connected to a local secondary CU that just serves a small home-salon and this toilet.

Manufacturers manual suggests a 3A FCU but do I really need to?

If maintenance has to be carried out the whole circuit can be isolated at the MCB without affecting the main house.  This is not the only toilet in the house and it gets plenty of light during the day.

Fan is 17W on a 240V circuit so if it's using anywhere near enough to blow a 3A FCU there is a serious problem.
 

Offline Gyro

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Re: UK toilet extractor fan
« Reply #1 on: August 17, 2021, 06:24:22 pm »
Unfortunately, the IET wiring regs always defer to the manufacturer's instructions. If the manufacturer specifies a 3A fuse, then there must be a 3A fuse to meet the regs.

The requirement is that an electrician must be able to isolate the fan to work on it in safety. It's debatable whether natural daylight is sufficient if it's a dull rainy day or evening call-out. Isolating the lighting circuit at the MCB may be sufficient, but in the case of a serious fan fault (smoke) means that you can't get the lights back on... but this is all secondary to the wiring regs requirement that I mentioned above, you need to fuse it at 3A to be compliant.


P.S. If you look at the Toolstation website for Click Grid modules, it's possible to fit a 3 pole fan isolator switch (Permanent live, switched live, and Neutral) and a fuseholder into a single width front plate. Product codes 75262, 93193, and 49473. Not expensive.
« Last Edit: August 17, 2021, 06:35:28 pm by Gyro »
Best Regards, Chris
 

Offline MajorbobTopic starter

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Re: UK toilet extractor fan
« Reply #2 on: August 17, 2021, 06:41:02 pm »
Ok, thank you for the clarification.  That's a minor irritation but not a problem.  I have a spare FCU I bought for another project and a single gang backplate so easy enough.
 

Offline eti

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Re: UK toilet extractor fan
« Reply #3 on: August 17, 2021, 07:18:41 pm »
One uses the word "lavatory", if one has any breeding and civility.
 

Offline Monkeh

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Re: UK toilet extractor fan
« Reply #4 on: August 17, 2021, 07:33:58 pm »
One uses the word "lavatory", if one has any breeding and civility.

And the rest of us just say bog.
 
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Offline floobydust

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Re: UK toilet extractor fan
« Reply #5 on: August 17, 2021, 07:36:33 pm »
In North America there have been bathroom fan fires, they are fed by the branch circuit 15A breaker, and locked-rotor causes them to overheat, so I would welcome any small fuse addition. I think newer fan motors have internal TCO but not older ones made for many decades.
It was not the hot chili and burritos that fueled the fire.
 

Online Zero999

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Re: UK toilet extractor fan
« Reply #6 on: August 17, 2021, 09:42:45 pm »
One uses the word "lavatory", if one has any breeding and civility.

And the rest of us just say bog.
Or shitehouse.

Regarding the original post: just use a 3A fused spur, which gives you the advantage of being about to isolate the fan, so it can be serviced, whilst keeping the lights on.
 

Offline Gyro

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Re: UK toilet extractor fan
« Reply #7 on: August 17, 2021, 10:01:00 pm »
Regarding the original post: just use a 3A fused spur, which gives you the advantage of being about to isolate the fan, so it can be serviced, whilst keeping the lights on.

An FCU (fused connection unit) is a fused spur - normally the one with a flex outlet.

To be completely accurate, the fan can only be serviced whilst the lights are on apart from the toilet / lavatory / shithouse one. The fan has a permanent live (via the fuse) and a switched live (from the switch or light fitting). Hence the use of multi-pole fan isolators.
Best Regards, Chris
 

Online themadhippy

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Re: UK toilet extractor fan
« Reply #8 on: August 17, 2021, 10:03:29 pm »
Quote
just use a 3A fused spur, which gives you the advantage of being about to isolate the fan,
The fan has a timer built in so will have a permanent live,switch live and a neutral,and  will require a 3 pole switch to safely isolate all current carrying conductors .
 

Online Halcyon

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Re: UK toilet extractor fan
« Reply #9 on: August 17, 2021, 10:22:47 pm »
One uses the word "lavatory", if one has any breeding and civility.

And the rest of us just say bog.

Wizz palace
 

Offline MajorbobTopic starter

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Re: UK toilet extractor fan
« Reply #10 on: August 17, 2021, 10:36:06 pm »
The fan has a timer built in so will have a permanent live,switch live and a neutral,and  will require a 3 pole switch to safely isolate all current carrying conductors .

For now, it will just get whatever switch faceplate I have available.  When I get round to it I'll upgrade it to a 3 pole.  (Probably when it either goes wrong or I sell the house if its anything like the "temporary" measures I usually come across)

For those who are so inclined, they may refer to the room as "guest facilities".
« Last Edit: August 17, 2021, 10:37:51 pm by Majorbob »
 

Online themadhippy

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Re: UK toilet extractor fan
« Reply #11 on: August 17, 2021, 10:51:47 pm »
in that case i'd wire the permanent live  to the live side of the spur and the switched live to the neutral side ,that way you are able to switch off both lives.
 

Online Zero999

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Re: UK toilet extractor fan
« Reply #12 on: August 19, 2021, 06:18:15 pm »
Regarding the original post: just use a 3A fused spur, which gives you the advantage of being about to isolate the fan, so it can be serviced, whilst keeping the lights on.

An FCU (fused connection unit) is a fused spur - normally the one with a flex outlet.

To be completely accurate, the fan can only be serviced whilst the lights are on apart from the toilet / lavatory / shithouse one. The fan has a permanent live (via the fuse) and a switched live (from the switch or light fitting). Hence the use of multi-pole fan isolators.
That's true. It does seem odd that the fan requires a 3A fuse, yet the timer is designed to connected to a standard 6A lighting circuit. If you're really paranoid, you could put the light on a 3A spur.
 

Offline Monkeh

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Re: UK toilet extractor fan
« Reply #13 on: August 19, 2021, 06:28:20 pm »
Regarding the original post: just use a 3A fused spur, which gives you the advantage of being about to isolate the fan, so it can be serviced, whilst keeping the lights on.

An FCU (fused connection unit) is a fused spur - normally the one with a flex outlet.

To be completely accurate, the fan can only be serviced whilst the lights are on apart from the toilet / lavatory / shithouse one. The fan has a permanent live (via the fuse) and a switched live (from the switch or light fitting). Hence the use of multi-pole fan isolators.
That's true. It does seem odd that the fan requires a 3A fuse, yet the timer is designed to connected to a standard 6A lighting circuit. If you're really paranoid, you could put the light on a 3A spur.

It likely calls for the fuse in both permanent and switched lines. The manufacturers need to learn to protect their own damn equipment.
 

Offline Gyro

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Re: UK toilet extractor fan
« Reply #14 on: August 19, 2021, 06:48:17 pm »
That's true. It does seem odd that the fan requires a 3A fuse, yet the timer is designed to connected to a standard 6A lighting circuit. If you're really paranoid, you could put the light on a 3A spur.

They're normally combined units these days (ie. timed [Edit: run-on] fans), with the fuse protecting both the fan motor and the timer circuit. 3A does seem high considering the contents - normally a resistor dropper, shunt zener regulation, CD4xxx IC and a TO92 Triac a few passives and a preset pot, but 3A is the lowest commonly available value so I guess that's the reason.

Most (I can't say all) fans just call for a fuse on the permanent line - otherwise you would be fusing the light fitting too (not that it would be a bad thing though).

I recently had to repair one of our fans, the under-rated electrolytic across 15V CD40xx logic supply had gone short (not leaked). The mains dropper resistor was still merrily dropping mains with a few % additional dissipation. After a decade or so of use, the phenolic PCB and plastic casing around and above it was a little browned, but no fuse on earth would really stop it melting down if it wanted to. The switched line isn't much of a risk because it goes straight to a decent body size high value series resistor to be clamped and rectified as a logic input.

« Last Edit: August 19, 2021, 07:01:11 pm by Gyro »
Best Regards, Chris
 

Offline james_s

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Re: UK toilet extractor fan
« Reply #15 on: August 19, 2021, 09:33:55 pm »
In North America there have been bathroom fan fires, they are fed by the branch circuit 15A breaker, and locked-rotor causes them to overheat, so I would welcome any small fuse addition. I think newer fan motors have internal TCO but not older ones made for many decades.
It was not the hot chili and burritos that fueled the fire.

I've seen the result of it. Those little shaded pole motors run hot under the best of conditions, I don't think a locked rotor greatly increases the current draw of one but it does remove the cooling airflow. The fact that it is normally full of dust bunnies adds additional thermal insulation and fuel and then it sits there and cooks until it catches fire. I'm not sure a fuse would do much good actually, but a thermal fuse in the motor would certainly be a good idea. I would assume the modern ones have one but I have not looked.
 

Online Zero999

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Re: UK toilet extractor fan
« Reply #16 on: August 20, 2021, 08:37:52 am »
That's true. It does seem odd that the fan requires a 3A fuse, yet the timer is designed to connected to a standard 6A lighting circuit. If you're really paranoid, you could put the light on a 3A spur.

They're normally combined units these days (ie. timed [Edit: run-on] fans), with the fuse protecting both the fan motor and the timer circuit. 3A does seem high considering the contents - normally a resistor dropper, shunt zener regulation, CD4xxx IC and a TO92 Triac a few passives and a preset pot, but 3A is the lowest commonly available value so I guess that's the reason.

Most (I can't say all) fans just call for a fuse on the permanent line - otherwise you would be fusing the light fitting too (not that it would be a bad thing though).
When I said the timer being connected to a 6A lighting circuit, I was talking about the timer input to the light switch.

Quote
I recently had to repair one of our fans, the under-rated electrolytic across 15V CD40xx logic supply had gone short (not leaked). The mains dropper resistor was still merrily dropping mains with a few % additional dissipation. After a decade or so of use, the phenolic PCB and plastic casing around and above it was a little browned, but no fuse on earth would really stop it melting down if it wanted to. The switched line isn't much of a risk because it goes straight to a decent body size high value series resistor to be clamped and rectified as a logic input.

I haven't wired up one of those fans before though. I did install one in my parents' house, but it was on a pull cord, rather than a timer. I'd be surprised if they still use CMOS logic ICs, rather than a microcontroller these days.
 

Offline Gyro

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Re: UK toilet extractor fan
« Reply #17 on: August 20, 2021, 09:57:38 am »
I don't think these things change much. A micro would require reasonable regulation rather than a simple 12-15V zener. It must also directly drive a mains Triac - a few more volts helps you get to a safer value gate resistor. The 40xx IC is nothing more than a cheap impedance converter / Schmitt trigger. The run-on time is set by simple electrolytic R/C network with preset pot. Easier than a dip switch, strange light switch on-off sequence etc. They normally come preset to the standard 20 mins anyway. It's a tried and tested reliable solution (even using a resistive rather than capacitive dropper helps there too, no self-healing failures). It would be hard to justify a micro on the basis of a BOM cost reduction here. The PCB must be big enough to hold the mains terminals too, so no board area reduction.

Example...

« Last Edit: August 20, 2021, 10:05:06 am by Gyro »
Best Regards, Chris
 

Online Zero999

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Re: UK toilet extractor fan
« Reply #18 on: August 20, 2021, 10:30:05 am »
I don't think these things change much. A micro would require reasonable regulation rather than a simple 12-15V zener. It must also directly drive a mains Triac - a few more volts helps you get to a safer value gate resistor. The 40xx IC is nothing more than a cheap impedance converter / Schmitt trigger. The run-on time is set by simple electrolytic R/C network with preset pot. Easier than a dip switch, strange light switch on-off sequence etc. They normally come preset to the standard 20 mins anyway. It's a tried and tested reliable solution (even using a resistive rather than capacitive dropper helps there too, no self-healing failures). It would be hard to justify a micro on the basis of a BOM cost reduction here. The PCB must be big enough to hold the mains terminals too, so no board area reduction.

Example...


That's a 14 pin DIP. I wonder if it's the CD4541B.

I suppose it's not surprising it's still done the old fashioned way: no software or programming to worry about.
 

Offline Gyro

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Re: UK toilet extractor fan
« Reply #19 on: August 20, 2021, 11:17:59 am »
No I think it's a CD4093 if memory serves, no counting happening, just the RC time constant. Switched line charges it up via a resistor, diode, and clamp and then it slowly discharges when the light is turned off. There are 2 electrolytics, one for the supply and one for the RC. A couple of diodes, zeners and resistors, a dropper resistor and TO92 triac and you're done. You're always going to be lumbered by through hole stuff anyway.

Yes, there's a lot to be said for not being dependent on a single silicon manufacturer (particularly right now) and mask / flash or whatever. It's all generic commodity stuff.

P.S. The dropper only needs to supply enough current for the 4093 quiescent and the triac trigger current, plus a bit of safety margin.
« Last Edit: August 20, 2021, 11:25:46 am by Gyro »
Best Regards, Chris
 

Offline SteveyG

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Re: UK toilet extractor fan
« Reply #20 on: August 20, 2021, 11:20:12 am »
Unfortunately, the IET wiring regs always defer to the manufacturer's instructions. If the manufacturer specifies a 3A fuse, then there must be a 3A fuse to meet the regs.

It's not quite phrased that way any more, since 18th edition it just says "shall take account of", meaning take note, but not necessarily follow. The wording was changed since so many import products had badly written or incorrect instructions.

A 3A BS1362 fuse will not offer any discrimination compared to a B6 MCB so it is not providing any electrical benefit, however if there is a warranty claim on the fan they may not offer the warranty if it is not installed according to their instructions.

An isolator for the fan is not a requirement either, since the MCB is noted as a suitable isolation device (Table 537.4)

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Offline Gyro

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Re: UK toilet extractor fan
« Reply #21 on: August 20, 2021, 11:41:17 am »
Unfortunately, the IET wiring regs always defer to the manufacturer's instructions. If the manufacturer specifies a 3A fuse, then there must be a 3A fuse to meet the regs.
It's not quite phrased that way any more, since 18th edition it just says "shall take account of", meaning take note, but not necessarily follow. The wording was changed since so many import products had badly written or incorrect instructions.

You might have some explaining to do if the manufacturer specifies a 3A fuse, you didn't fit one, and it happens to catch fire though.

Quote
A 3A BS1362 fuse will not offer any discrimination compared to a B6 MCB so it is not providing any electrical benefit...

Yes, I agree.

Quote
An isolator for the fan is not a requirement either, since the MCB is noted as a suitable isolation device (Table 537.4)

As long as safe isolation and servicing can be carried out in a safe manner - that includes sufficient lighting. They wouldn't be making and fitting them if there wasn't a pretty good justification though... such as being able to disable it if you get up for a pee in the night! *

For ducted loft ones, the sort of connectors they use for downlight wiring are pretty good. You can simply and safely unplug the fan without touching the breaker and pull it out and work on it in comfort (they're fiddly to wire at the best of times). Eg: The Greenbrook ones at Screwfix, £2.49 saves an awful lot of hassle... https://www.screwfix.com/p/greenbrook-20a-4-way-connector/176gv




P.S.  * The ECA opinion...

« Last Edit: August 20, 2021, 12:00:50 pm by Gyro »
Best Regards, Chris
 

Online Zero999

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Re: UK toilet extractor fan
« Reply #22 on: August 20, 2021, 12:26:34 pm »
No I think it's a CD4093 if memory serves, no counting happening, just the RC time constant. Switched line charges it up via a resistor, diode, and clamp and then it slowly discharges when the light is turned off. There are 2 electrolytics, one for the supply and one for the RC. A couple of diodes, zeners and resistors, a dropper resistor and TO92 triac and you're done. You're always going to be lumbered by through hole stuff anyway.

Yes, there's a lot to be said for not being dependent on a single silicon manufacturer (particularly right now) and mask / flash or whatever. It's all generic commodity stuff.

P.S. The dropper only needs to supply enough current for the 4093 quiescent and the triac trigger current, plus a bit of safety margin.
I'm surprised they would choose a simple RC circuit, for such a long delay, because it would require a high value resistor and capacitor.
 

Offline SteveyG

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Re: UK toilet extractor fan
« Reply #23 on: August 20, 2021, 12:40:13 pm »

You might have some explaining to do if the manufacturer specifies a 3A fuse, you didn't fit one, and it happens to catch fire though.

As long as safe isolation and servicing can be carried out in a safe manner - that includes sufficient lighting. They wouldn't be making and fitting them if there wasn't a pretty good justification though... such as being able to disable it if you get up for a pee in the night! *


A 3A fuse will not prevent a fire however  :-// A 3A BS1362 will carry 6A indefinitely so over 1kW

Servicing doesn't require lighting from the existing electrical installation otherwise how would you service the lighting, or complete an installation before energised?  :o
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Offline Gyro

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Re: UK toilet extractor fan
« Reply #24 on: August 20, 2021, 12:53:50 pm »
I'm surprised they would choose a simple RC circuit, for such a long delay, because it would require a high value resistor and capacitor.

Yes, a 4541 would make sense wouldn't it. Not the way it was wired when I was fault tracing though. I'm pretty sure it was just quad 2 input gate. I'm not pulling it apart to double check though.  ;)  There's probably some reason, maybe they needed to parallel 3 outputs to drive the triac or something, or just didn't think of it. Upping the capacitor and resistor values wouldn't cost them anything. I don't know.
Best Regards, Chris
 


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