Standard inline extractor fan

[fatcontroller]

Good morning all, I am new here and need your help and advice. I am changing a fan in en-suite from a timer unit to a two speed inline non timer unit, I also have to connect through a new fused 3A switch unit. I have confirmed which cable does what but I have hit a snag as regards the switch live 2 core cable from the ceiling rose and the 3 core cable from the light switch.
The 2 core from ceiling rose consists of Live and the other core is being used as earth. The 3 core E N L is coming straight from the switch. I have established that the 3 core live isn't needed as the fan will run non stop. The unit being fitted has L N connections and doesn't need earth cable. Here come the questions:

a) do I isolate the 3 core cables (from switch) into a bloc and not use any of these cores at all?full disconnection would be better but want to keep cable in place in case I ever get another timer unit
b) untwist the earth core from 2 core cable (ceiling rose) and use as a neutral, therefore creating a L N connection for fan, if so, does it go in connection next to the second neutral cable already in the rose?
c)connect the Live and newly created Neutral into the fuse switch box?
d)connect L to fan unit and N to whichever speed connection I want to use in the unit?

Many thanks in advance

 

[endecotp]

Why a new 3A fuse? If it's on a 6A lighting circuit, that will be sufficient protection.

 

[endecotp]

This cable with perm live and earth, what colour are the conductors?

 

[fatcontroller]

Why a new 3A fuse? If it's on a 6A lighting circuit, that will be sufficient protection.

Manufacturer says to fit fuse switch

 

[fatcontroller]

This cable with perm live and earth, what colour are the conductors?

I assume you mean the 3 core cable, if so, red, blue, earth

 

[endecotp]

Ignore the instructions. (Or rather, "have regard" to them, but don't follow them blindly.) Is there a 6A MCB protecting the circuit? You need an isolator switch.

No, I mean the cable with the permanent live and earth.

 

[fatcontroller]

The live from rose is red and other core is unsheathed and being used as earth, the fan runs non stop when connected to the three core from switch.

 

[endecotp]

if it's unsheathed you can't use it as anything other than an earth.

 

[fatcontroller]

If your timer fan worked as it should have then all you had to do was connect the Switched Live wire (Timer connection) and Neutral to the new fan. Safely terminating the Permanent Live out of the way.

Found this on another thread, looks like the same sort of question as mine, 'SAFELY TERMINATING LIVE OUT OF THE WAY' does that mean the entire cable or just the Live? If only the live is terminated, do I then connect only the switch live and leave the unsheathed core disconnected and still use the neutral and earth from the switch cable?

if it's unsheathed you can't use it as anything other than an earth.

What do I have to do to wire the fan?

 

[endecotp]

Let me make sure I understand what you want to do. You wrote "two speed fan", but you aren't actually trying to use two speeds, are you? (Sometimes fans are connected to run continuously at a very slow speed and then boost when necessary.). You want to use just one speed, and for the fan to run only when the light is on. It that correct?

So you need to:
- Connect all the earths together.
- Connect a switched live and a neutral to the fan, via an isolator switch.

It soinds like the switched live is the one coming from the ceiling rose, and your only neutral comes from the switch. I find that a little but surprising, but it's plausible.

I suggest that you get a 3-pole fan isolator switch. You don't need the third pole, but (a) these switches say "fan" on them, which helps identification, (b) it gives you somewhere to terminate the unused permanent live, and (c) it will help in the future when you change back to a timer fan.

 

[fatcontroller]

Only using one speed and fan to run when light switch turned on, correct.

To clarify, I should connect the earth from rose to the earth in switch cable and use neutral and earth from 3 core permanent live cable alongside the switch live from the rose, isolating permanent live in isolator switch box?

 

[endecotp]

that sounds right.

 

[fatcontroller]

Many thanks, the point you made about only neutral coming from permanent live being surprising but plausible, is that still safe?

 

[endecotp]

it's safe, assuming that you haven't misunderstood what's going on.
there is a possibility of induced hum in hifi speakers and hearing aids when the live and neutral take different paths.
if you have any metal boxes, you should make sure the live and neutral both enter through the same hole.
I presume it would be difficult to run a new 3-core-and-earth wire from the switch to the fan, right?

 

[endecotp]

(you do have another option which is to change the wiring at the switch so that you have switched live and neutral on the cable from the switch. you could then ignore the wire from the ceiling rose. this has the disadvantage that it would be more difficult to change back to a timer fan. my guess is that the current arangement is a result of changing from non-timer to timer at some point in the past.)