Yet another bathroom extractor fan (with timer) installation question...

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Hi all,

There's a lot of debate all over the forums about extractor fans, specifically timer ones, and how they should be installed.

I'm not an electrician but as far as I'm aware to meet regs the following is needed:

1. A fan isolator switch (located outside of the bathroom).
2. 3a FCU (if manufacturer instructions state this, located outside of the bathroom).

I've recently moved into a house and at the moment I have an in-line extractor fan located in the loft (no timer). It's turns on/off instantly with the light switch. The power to the bathroom is fused with a 3a FCU with the power coming from the previous light in bedroom 1 and this FCU is located above door height in the bathroom. I believe this is zone 2 and I'm not sure if this meets regs now or ever did (guess the bathroom was installed within the last 10 years).

What I'd like to do is replace the existing fan (it's incredibly loud and annoying, even in the loft) with a new quieter in-line fan but with a timer. Our bathroom has no window so I think a delayed timer function is much better and also meets regs.

Now, I think this bit is simple. A 3 core and earth cable from the light rose to an isolator switch (located outside the bathroom) and from the isolator to the new fan. Simples...(at least, I think it is).

The thing that's bugging me is this existing FCU. It's intercepting the previous ceiling rose cable. So if this fuse goes, it does it's job of cutting off the supply to the bathroom (light and fan) but also all of the remaining lights on the circuit. In this case, the bedroom 2 and landing light.

This has lead to me wondering:

1. Is this standard practice or is it best to configure the FCU in a way so it's only isolating the bathroom and not the remaining lights on the circuit?

2. Is an FCU above bathroom door height (inside zone 2 of the bathroom) passing regs or is it best to move the FCU outside the bathroom next to the new isolator switch?

3. Does an FCU for 3 core and earth cable exist? It would be much better to just fuse down the 3 core and earth (both switch live and permanent live) just before the isolator switch wouldn't it? Even better, an isolator switch with built in fuses for both switch and live).

Thanks,
Steve
 
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Buy a fan for which the manufacturer does not require a 3A fuse and start again.

It would be better if the FCU did not control the light.
FCUs for three cores (the earth must not be switched) do not exist.
Zone two is only vertically within 600mm. from the edge of the bath/shower up to 2250mm. from the floor level.
 
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Thanks for the reply, it's much appreciated. Out of interest, what would be the best configuration if a 3A fused FCU was needed and buying a fan for which the manufacturer does not require this isn't possible? I'll definitely go down that route but out of interest it would be great to know the best cable config between incoming power from previous lighting to the FCU, bathroom light, switch and timer fan. I've looked for some example diagrams and can't seem to find any for this set up.
 
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Thanks for this, so I'd need a double pole light cord as well as using a switched FCU instead of an isolator. And much more complicated cabling with this set up. Why would any manufacturer that make timer fans make people do this :)
 
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Now, I think this bit is simple. A 3 core and earth cable from the light rose to an isolator switch (located outside the bathroom) and from the isolator to the new fan. Simples...(at least, I think it is).

That is the usual method.
The existing FCU has no purpose and would be removed completely.

While certain fan manufacturers have instructions that state a 3A FCU is required, it serves no purpose other than to increase the cost and complexity of the installation.
Even in the event of a fault, it's highly likely that a 6A MCB will operate before the 3A fuse anyway.
 
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That is the usual method.
The existing FCU has no purpose and would be removed completely.

While certain fan manufacturers have instructions that state a 3A FCU is required, it serves no purpose other than to increase the cost and complexity of the installation.
Even in the event of a fault, it's highly likely that a 6A MCB will operate before the 3A fuse anyway.

Thanks, I've heard this a lot. Do electricians ignore the instructions and instead do not fit a 3A FCU even if it's stated? Even though it serves no purpose, just to get passed the red tape and so it satisfies regs.

Even though there is an existing FCU in my bathroom, would you still recommend it be removed and to connect the ceiling rose > isolator switch > timer fan?

There's a lot of conflicting info but I know there are many ways to skin this cat. I guess it's because the regulations are illogical. To do everything correctly by the book means more cost, materials and complexity for something that experienced electricians are saying is pointless anyway and is not necessarily any safer.
 
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The fact is that the 3A fuse is definitely not required for electrical reasons.

However, regulations state that manufacturers instructions should be followed (slightly reduced lately, to 'taken into consideration').

Some MIs are clearly wrong, some misleading and some just puzzling.

It's your house. :)
 
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Do electricians ignore the instructions and instead do not fit a 3A FCU even if it's stated? Even though it serves no purpose, just to get passed the red tape and so it satisfies regs.
There are no regulations which require fans to have a 3A FCU.

It's something entirely invented by fan manufacturers, and the only reason for fitting one is if you wish to comply with what someone who worked there decided to put into the instructions.
 
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And BTW - the regulations do not require a timed overrun fan (although you might well prefer one), and they do not require that it automatically come on with the lights (and you might well prefer that it did not).
 
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