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PostPosted: Sun Mar 11, 2018 9:32 am 
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Okay, so I recently ordered myself a couple of in line duct fans, one for my bathroom and one for my kitchen. I ordered a timer model for the bathroom which comes complete with a wiring diagram on how to wire it on the lighting circuit, which is all nice and straightforward.

The kitchen fan that I ordered is the same model, just 6" instead of 4". I also ordered this one as just a standard unit, not a timer model. However, I have recieved the timer model 6" fan and now that I think about it, I wouln't mind the kitchen fan staying on for a short while after I've turned it off. My initial plan was to just have it operated by a switched FCU in the kitchen, nice and simple.

Like I said before, the fans came with wiring diagrams, although the timer fan diagram is set out with the fan being on the lighting circuit. I don't want the kitchen fan to come on when I turned the kitchen light on, I would still like it to just be operated by the switched FCU. What I'm struggling to figure out is how I would need to wire it from this FCU to the fan, in order to have the timer function work?

Would it be a matter of running 3 core & earth from the FCU to a 3 pole isolator switch and from there to the fan? Or would I need to set up some kind of junction box to replicate the set up you would find on a lighting circuit? Any help or advice anyone could give me with this would be much appreciated, thanks!


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PostPosted: Sun Mar 11, 2018 9:45 am 
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You can't "switch it off" via the FCU AND have it "over run" The reason is although you know now, later on, or any one else switching it off at the FCU would not expect the fan to still be live (Via the over run)

You could connect the FCU to your ring, then a switch for your fan, then to the Fan / and fan isolator. Just like your bathroom fan is.

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PostPosted: Sun Mar 11, 2018 11:48 am 
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Okay, just so we're clear (please bare with me, I'm fairly new to all this electrical stuff), what you're saying is I could connect an FCU to the ring main (the current fan is connected to one, that is spurred off of the ring at a junction box, I presume this isn't an issue?), connect a separate switch to that FCU and then from that switch go to the fan/isolator switch in 3 core&earth?

Is there no way I could operate the fan with the over run soley through the FCU? I just don't fancy having any more switches on the kitchen wall if I don't need them, I'm doing this work now as I'll be fitting a new kitchen pretty soon afterwards.

I've looked over the internet for wiring diagrams for this kind of setup, as they much it all so much clearer to me. Unfortunately, every one I've come across has been set out with a lighting circuit in mind. Any chance you know of one that would be suitable for my situation?


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PostPosted: Sun Mar 11, 2018 1:37 pm 
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I will try and fill in the gaps.

You MUST have a means of protecting the smaller cable when you connect to a ring main (Your current switched FCU is ok)
You then want to be able to turn the fan on / off. To do this means you need............another switch (sorry)
When your switch is turned on it does so by telling the over run timer to start.
When you switch your fan off, the over run timer carries on running the fan as that is what it is meant to do.
A triple pole fan isolator adj the fan cuts off Live, neutral and switched live to the fan so it is safe to work on.
If you were to wire it as you assumed, switching the FCU on/off is by passing the over run timer, so it will not work as you want. (That said, it could be done, but would be extremely dangerous, if not lethal)

So that is why you need a switch, and FCU and a triple pole isolator.

You do how ever have 2 more options

Use a pull cord switch to turn the fan on/off
Don't use the over run timer option, that way you can use the FCU to turn the fan on/off

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PostPosted: Sun Mar 11, 2018 2:00 pm 
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someone-else wrote:
So that is why you need a switch, and FCU and a triple pole isolator.


There is no need for a triple pole isolator if the circuit if fed from a double pole SFCU. All that is needed is a seperate switch AFTER the SFCU.


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PostPosted: Sun Mar 11, 2018 5:17 pm 
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Right, I think I've finally figured it out (thanks for your help with that someone-else!). I'm just going to put it into words and if it makes sense, could you please tell me if what I'm saying is correct? I apologize if my description of everything makes things difficult to understand.

So I can spur off of the ring main to an FCU in 2.5 T&E.

From that FCU, I can run a length of 1.5T&E to a junction box.

In this junction box, I can connect the incoming 1.5T&E to connector blocks, which will also have 1.5T&E connected between them and a 3 pole isolator switch.

To create a switch line for the fan, I can use a length of 1.5 T&E, with the live cable connected to the 'Live' connector block, to connect to the 'Live in' side of a 20A switch.

The neutral cable in this length of 1.5T&E will be connected to the 'Neutral load' side of the 20A switch, with the other end of the length of 1.5 T&E neutral cable connected to the 3 pole isolator switch.

From the 3 pole isolator switch, using 3 core cable, I can connect the live that is connected to the 'live' connector block, to the permanent live conncection on the fan.

I can connect the neutral that is connected to the 'neutral' connector block, to the neutral connection on the fan.

And then I can connect the switched live 'neutral coloured' cable to the switched live connection on the fan?


Will this work?


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PostPosted: Sun Mar 11, 2018 6:11 pm 
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A drawing would be easier. (and you don't need an additional junction box)

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PostPosted: Sun Mar 11, 2018 6:47 pm 
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Attachment:
Untitled 2.png
Untitled 2.png [ 55.44 KiB | Viewed 675 times ]
I hope this helps, this is what I was thinking might work.


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PostPosted: Sun Mar 11, 2018 6:53 pm 
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That's better. :thumbleft:

Yes, I see no reason it will not work.

I also would like to point out the following.
You don't need the junction box
You don't need a 20A switch for the fan. (Normal 6A switch will be fine)

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For this message the author someone-else has received gratitude : RJW91
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PostPosted: Sun Mar 11, 2018 7:23 pm 
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RJW91 wrote:
Attachment:
Untitled 2.png
I hope this helps, this is what I was thinking might work.



Looks fine to me, but the 3 pole isolator is not needed,



For this message the author OnlyMe has received gratitude : RJW91
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PostPosted: Sun Mar 11, 2018 7:35 pm 
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Excellent! Thanks again for all your help!

Just a couple of additional points I'd like to clear up for my own peace of mind, if you don't mind.

The reason I have included a junction box is because the connector blocks I plan on using are the Wago 222 series, which I believe Wago specify should be enclosed in one of their junction boxes. They don't cost much and I found them easy to use when I changed all of my ceiling roses to LED light fittings, so I thought they would work nicely in this project as well. I obviously need to tap into the live for the switched live connection, so this is where I thought I'd use one of the Wago 222 3 way connector blocks and consequently need to enclose it in one of their junction boxes. What makes you say I don't need a junction box?

The reason I decided on a 20A switch for the fan is simply because Crabtree sell a 20A switch which says 'Fan' on it, which I would rather have than just a standard light switch for example, I just think it would ultimately look better as it will highlight what the switch actually does and it matches the profile of all the other sockets/switches in my house. I moved into the place in December 2015 and the place is a bit of a doer-upper, having sockets/switches that match in profile, colour and finish is part of my vision for the place. Is there any reason why a 20A switch wouldn't be suitable in this situation? Like I said, I'm only really going for it for aesthetic reasons.

After coming to understand that I needed to run the whole thing after an FCU, I thought that I could do this and not have additional switches in the kitchen by positioning the FCU on the plywood frame I put up in the loft, fixed to the trusses with noggins in place to provide a secure point for fixing the fan to as well as any switch pattress boxes. Is there any reason why the FCU and fan isolator switch wouldn't be suitable up there, mounted to the plywood frame? I figured I might as well stick the fan isolator switch on the plywood frame, as if I need to isolate the fan to clean it up or whatever, I might as well have the switch next to the fan itself, as opposed to above the bathroom door which I understand is common practice?

Finally, where some previous owner of my house decided to put in a kitchen extractor fan, they or whoever installed the current one for some reason spurred off of the ring main with a junction box a couple of metres or so away in the loft from where the spur cable for the extractor fan drops down into the kitchen. I can't actually see why they couldn't have just extended the ring circuit and made the FCU for the current fan a new point on the ring circuit, as there are two points on the ring circuit between where the cable drops down for the extractor fan, but then that's going into territory I'm not too familiar with.

I'm just wondering if this for whatever reason could be an issue? Is a spur from the ring circuit ideally supposed to be limited to a certain distance in cable? I have considered doing away with what's there at the moment and just extending the ring circuit like I mentioned previously, or at least creating the spur at the point where the cable drops down into the kitchen, just not sure if it's really worth the bother.

But yeah, thanks again for all your help someone-else! All I need to do now is wait for a day with good weather so I can move the vent tiles around on the roof!


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PostPosted: Sun Mar 11, 2018 7:37 pm 
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OnlyMe wrote:
RJW91 wrote:
Attachment:
Untitled 2.png
I hope this helps, this is what I was thinking might work.



Looks fine to me, but the 3 pole isolator is not needed,


Is the 3 pole isolator purely there to isolate the fan entirely if I needed to clean it or something? For that reason I wouldn't mind having one there, is there any reason why there shouldn't be one?


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