UK toilet extractor fan - Page 1
Forum section: electronics / general

author: Majorbob
author_rank: Regular Contributor
timestamp: August 17, 2021, 05:48:44 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: August 17, 2021, 06:24:22 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: August 17, 2021, 06:41:02 pm
content: 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.

author: eti
author_rank: Super Contributor
timestamp: August 17, 2021, 07:18:41 pm
content: One uses the word "lavatory", if one has any breeding and civility.

author: Monkeh
author_rank: Super Contributor
timestamp: August 17, 2021, 07:33:58 pm
content: Quote from: eti on August 17, 2021, 07:18:41 pmAnd the rest of us just say bog.

author: floobydust
author_rank: Super Contributor
timestamp: August 17, 2021, 07:36:33 pm
content: In North America there have beenbathroom 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.

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2021, 09:42:45 pm
content: Quote from: Monkeh on August 17, 2021, 07:33:58 pmOr 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.

author: Gyro
author_rank: Super Contributor
timestamp: August 17, 2021, 10:01:00 pm
content: Quote from: Zero999 on August 17, 2021, 09:42:45 pmAn 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 onapartfrom 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.

author: themadhippy
author_rank: Super Contributor
timestamp: August 17, 2021, 10:03:29 pm
content: QuoteThe 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 .

author: Halcyon
author_rank: Unknown
timestamp: August 17, 2021, 10:22:47 pm
content: Quote from: Monkeh on August 17, 2021, 07:33:58 pmWizz palace

author: Majorbob
author_rank: Regular Contributor
timestamp: August 17, 2021, 10:36:06 pm
content: Quote from: themadhippy on August 17, 2021, 10:03:29 pmFor 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".

author: themadhippy
author_rank: Super Contributor
timestamp: August 17, 2021, 10:51:47 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: August 19, 2021, 06:18:15 pm
content: Quote from: Gyro on August 17, 2021, 10:01:00 pmThat'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.

author: Monkeh
author_rank: Super Contributor
timestamp: August 19, 2021, 06:28:20 pm
content: Quote from: Zero999 on August 19, 2021, 06:18:15 pmIt likely calls for the fuse in both permanent and switched lines. The manufacturers need to learn to protect their own damn equipment.

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2021, 06:48:17 pm
content: Quote from: Zero999 on August 19, 2021, 06:18:15 pmThey'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 youwouldbe 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.

author: james_s
author_rank: Super Contributor
timestamp: August 19, 2021, 09:33:55 pm
content: Quote from: floobydust on August 17, 2021, 07:36:33 pmI'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.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2021, 08:37:52 am
content: Quote from: Gyro on August 19, 2021, 06:48:17 pmWhen I said the timer being connected to a 6A lighting circuit, I was talking about the timer input to the light switch.QuoteI 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.

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 09:57:38 am
content: 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...

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2021, 10:30:05 am
content: Quote from: Gyro on August 20, 2021, 09:57:38 amThat'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.

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 11:17:59 am
content: 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.

author: SteveyG
author_rank: Unknown
timestamp: August 20, 2021, 11:20:12 am
content: Quote from: Gyro on August 17, 2021, 06:24:22 pmIt'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)

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 11:41:17 am
content: Quote from: SteveyG on August 20, 2021, 11:20:12 amYou 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.QuoteYes, I agree.QuoteAs 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/176gvP.S.*The ECA opinion...

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2021, 12:26:34 pm
content: Quote from: Gyro on August 20, 2021, 11:17:59 amI'm surprised they would choose a simple RC circuit, for such a long delay, because it would require a high value resistor and capacitor.

author: SteveyG
author_rank: Unknown
timestamp: August 20, 2021, 12:40:13 pm
content: Quote from: Gyro on August 20, 2021, 11:41:17 amA 3A fuse will not prevent a fire howeverA 3A BS1362 will carry 6A indefinitely so over 1kWServicing doesn't require lighting from the existing electrical installation otherwise how would you service the lighting, or complete an installation before energised?

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 12:53:50 pm
content: Quote from: Zero999 on August 20, 2021, 12:26:34 pmYes, 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.

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 01:13:02 pm
content: Quote from: SteveyG on August 20, 2021, 12:40:13 pmI agree with you. I'm not arguing that it makes sense. Just that's the way it's currently done / written. I didn't bother following up the additional references in the video.I suppose the onus is on the fan manufacturer to explain why they think a 3A fuse would make any difference to its safety.The only thing I can possibly think of is that a fan might get wired in 0.5mm flex (there's no way you're ever going to squeeze solid 1mm or 1.5mm 3 core+CPC in there - certainly on a ducted one). This wouldn't be sufficiently protected by a B6 MCB under the regs though. Sorry, I'm grasping for explanations - not knowing what the fan instructions say about the size of cable, I can't say though.

author: themadhippy
author_rank: Super Contributor
timestamp: August 20, 2021, 01:16:12 pm
content: As usual Bigclive has already dissected one.

author: richard.cs
author_rank: Super Contributor
timestamp: August 20, 2021, 01:29:21 pm
content: Somewhere I have the reverse-engineered schematic of mine, from when I modified to trigger from a current transformer. Notable points:It's a resistive dropper not a capacitive one.The switched live goes straight into a high-value resistor, so there really is no need to worry about fusing on that input.It's a quad-NOR configured as an RC timer, with a very high resistor value and a modest electrolytic, maybe 220 uF.I seem to remember the capacitor is normally charged and discharges to start the time delay (which ends once refilled), this may be because keeping the electrolytic biased reduces leakage current which would otherwise affect timing.The whole board is neutral-referenced.A small triac in the neutral is used to switch the motor.I can't really remember but I think the board may have been given a negative supply relative to neutral, so as to allow negative gate drive for quadrant 2/3 operation and avoid quadrant 4.

author: Majorbob
author_rank: Regular Contributor
timestamp: August 20, 2021, 04:44:39 pm
content: Quote from: SteveyG on August 20, 2021, 11:20:12 amSo according to 18th edition I can ignore the manufacturers instructions? Any repairs and maintenance can be done during the day with the whole circuit off.

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 07:10:09 pm
content: 'Ignore' sounds like a pretty extreme interpretation of 'take account of'. There are clearly going to be cases (a lot of Chinese manufactured light fitting for instance), where the installation instructions are going to be wrong for the UK - eg. Not including instructions for earthing metal fittings. Something like specifying a specific fuse rating are less open to interpretation.What are you wiring the fan up with? will it directly accept standard 1.5mm2PVC solid 3 core and earth? Edit: Ah, they do make it in 1mm2, I didn't think they did.At the end of the day, I don't think anyone here is going to publicly tell you that you can ignore the manufacturer's instructions when personal safety, insurance etc. are involved.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2021, 07:21:08 pm
content: Quote from: themadhippy on August 20, 2021, 01:16:12 pmThe values seem to be on the low side: 470µF & 440k. I'll have to do some calculations to see what the delay will be.

author: floobydust
author_rank: Super Contributor
timestamp: August 20, 2021, 07:51:31 pm
content: How can you import and sell cheap chinese bathroom fans in the UK, when they have no safety or agency approvals? OP, ensure your product is legit.Yet we're worried about fusing and the ET Wiring Regulations. Like a fox in the henhouse.The Big Clive fan, wasting 1.2W all the time- looking at the cooked 22k resistor, phenolic pcb, unknown plastic housing (UL 94V??) it's your usual POS.I've seen other fans with electronics such as MCU and PIR sensor, use instead a capacitive dropper.The only safety component is the dropping resistor, hopefully they are infallible. Not so with thick-film TO-220 resistors for some reason, I've seen them go lower in value with abuse.This looks like metal-oxide running hot 24/7 just to power a CMOS timer

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 07:57:21 pm
content: Quote from: Zero999 on August 20, 2021, 07:21:08 pmI think Clive is out on the pot value, he didn't measure it but said it was marked C05, so it might be 500k (or even 5M?). The 220k fixed resistor is a minimum value limiter, so I would expect the pot to be significantly higher (I'm not sure what the minimum and maximum times are).

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2021, 08:45:13 pm
content: Quote from: Gyro on August 20, 2021, 07:57:21 pmIt looks like 605 to me, or perhaps 1605 which is 6M, or 16M. which are odd values, but wouldn't be surprising.It took a screenshot and upped the contrast a little to make it clearer.

author: Gyro
author_rank: Super Contributor
timestamp: August 20, 2021, 09:03:47 pm
content: Sounds right to me, I'd guess at 6M rather than 16.

author: Majorbob
author_rank: Regular Contributor
timestamp: August 21, 2021, 08:56:26 am
content: Quote from: Gyro on August 20, 2021, 07:10:09 pmMaybe "ignore" was the wrong terminology. I'm asking here so clearly I have "taken account of" the instructions. Its the cheapest fan B&Q had on their shelf so it not complete chinese rubbish.I can't remember if I have 1 or 1.5mm t&e of the top of my head but the whole installation is brand new.

author: Monkeh
author_rank: Super Contributor
timestamp: August 21, 2021, 01:28:16 pm
content: Quote from: Majorbob on August 21, 2021, 08:56:26 am.. no, that means it absolutely is complete rubbish. B&Q have a long history of products which catch fire.

author: Majorbob
author_rank: Regular Contributor
timestamp: August 21, 2021, 11:33:34 pm
content: It's a manrose vxf100s, so I don't believe it's insta-fire.

author: floobydust
author_rank: Super Contributor
timestamp: September 05, 2021, 06:21:11 pm
content: I forgot to follow up.Manrose are a UK manufacturer "All fans are double insulated, manufactured to comply with EN60335-2-80:1997 and are CE marked"That's an (older) safety standard, for ceiling fans, desktop fans, worried about electric shock, kids sticking their fingers in the blades etc. and apparently it has thermal tests/locked rotor heating so if they actually are certified product, it's not off the junk.

author: Monkeh
author_rank: Super Contributor
timestamp: September 05, 2021, 06:29:28 pm
content: Quote from: floobydust on September 05, 2021, 06:21:11 pmIt's an ancient, extremely low end model they won't even acknowledge exists any more, and to this day they sell products which don't take into account the wiring systems they're to be conneced to. It's junk. Perhaps not a fire (yet), but crap nonetheless.

author: floobydust
author_rank: Super Contributor
timestamp: September 05, 2021, 06:47:35 pm
content: What is it that makes it junk? UK seems to be possible to dodge the safety standards with "designed to" or just not mention any standards, or hype the one environmental standard it achieves. "manufactured to comply" does not mean it actually was tested/evaluated and does comply.It's probably a chinese fan motor and just locally assembled to claim "made in the UK". I see many importers of chinese junk reselling it locally sans safety approvals. What a way to make money- peddling unsafe crap.The 3A fuse is not enough to prevent a fan or circuit board fire, I'm not sure what it's good for really. Protecting the wiring?

author: Gyro
author_rank: Super Contributor
timestamp: September 05, 2021, 07:37:55 pm
content: Quote from: floobydust on September 05, 2021, 06:47:35 pmYes, that's my take on it, It's probably thin stranded flex (I've never had any luck getting solid T&E in there!), which may not be fully captured. Widespread, non-industrial, availability of ferrules seems to be a recent thing.