General > General Technical Chat
UK toilet extractor fan
SteveyG:
--- Quote from: Gyro 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.
--- End quote ---
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)
Gyro:
--- Quote from: SteveyG on August 20, 2021, 11:20:12 am ---
--- Quote from: Gyro 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.
--- End quote ---
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.
--- End quote ---
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...
--- End quote ---
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)
--- End quote ---
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...
Zero999:
--- Quote from: Gyro 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.
--- End quote ---
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.
SteveyG:
--- Quote from: Gyro on August 20, 2021, 11:41:17 am ---
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! *
--- End quote ---
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
Gyro:
--- Quote from: Zero999 on August 20, 2021, 12:26:34 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.
--- End quote ---
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.
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