Extractor Fan - FCU or Isolator Switch or Both?

[pbar]

Hi. I am installing a bathroom extractor fan with timer overrun, it's an inline one so the fan itself will be in the loft space above. I am thinking of taking the feed from a plug socket, as there is one up in the loft, not far from where the fan will be. So, I assume I will need an FCU to fuse it down. If that's correct, will I still need a triple pole isolator. And if so, is there a unit which combines the two?
Thanks.

 

[baz1968]

Has'nt someone already answered this

//www.diynot.com/forums/viewtopic.php?t=147708

 

[stem]

So long as the loft socket is on the ring (ie not a spur from the ring) you can spur off it to an FCU for a fan.

If the fan has a run-on timer, the isolator will need to isolate all three wires (live, switched live and neutral). It needs to be near the fan so that it can be switched off for maintenance.

You don't mention where the switched live comes from. If it's from the light in your bathroom, you should not use the FCU method as the lights are on a diferent circuit to sockets. If you are adding a separate switch for the fan, a PIR sensor or humidistat, you can use the FCU method provided that it is fed from the same FCU as the fan.

 

[pbar]

So long as the loft socket is on the ring (ie not a spur from the ring) you can spur off it to an FCU for a fan.

If the fan has a run-on timer, the isolator will need to isolate all three wires (live, switched live and neutral). It needs to be near the fan so that it can be switched off for maintenance.

You don't mention where the switched live comes from. If it's from the light in your bathroom, you should not use the FCU method as the lights are on a diferent circuit to sockets. If you are adding a separate switch for the fan, a PIR sensor or humidistat, you can use the FCU method provided that it is fed from the same FCU as the fan.

Thanks for your reply, I appreciate it.
I think I understand, although I didn't give you all the info. The fan will be operated by a separate pull cord switch.
The loft socket is a spur yes, so can I not use that then?
I intended to run a 3 core & earth cable from the plug socket, to an FCU (making sure both live's can be isolated), then to the the pull cord switch, then to the fan.
If this is not allowed, then I would run a 3 core & earth cable from a junction box for the upstairs lighting, to a triple pole fan isolator, then to the pull cord, then to the fan.
Are either, or neither, of these options ok?
Thanks!

 

[GaryMo]

Remember, the 3A fuse will need to protect both the permanent and switched live so would need to be situated before the bathrrom fitting.

 

[stem]

The fan will be operated by a separate pull cord switch.

That's OK then as the live and the switched live are fed from the same circuit.

The loft socket is a spur yes, so can I not use that then?

No, a spur feeding a socket cannot continue on to feed another spur.

If this is not allowed, then I would run a 3 core & earth cable from a junction box for the upstairs lighting, to a triple pole fan isolator, then to the pull cord, then to the fan.

Usually the pull cord comes first and the isolator is in the supply to the fan close to it, I don't really see a problem with what you propose as long as the isolator is close to the fan and it's obvious what it does.

 

[pbar]

The fan will be operated by a separate pull cord switch.

That's OK then as the live and the switched live are fed from the same circuit.

The loft socket is a spur yes, so can I not use that then?

No, a spur feeding a socket cannot continue on to feed another spur.

If this is not allowed, then I would run a 3 core & earth cable from a junction box for the upstairs lighting, to a triple pole fan isolator, then to the pull cord, then to the fan.

Usually the pull cord comes first and the isolator is in the supply to the fan close to it, I don't really see a problem with what you propose as long as the isolator is close to the fan and it's obvious what it does.

Great, thank you for that.
I just have 2 more points to mention/ask -
I thought the isolator would be better before both the pull cord and the fan, so both can become isolated if need be. Is that not better? I understand what you say that the isolator must be near the fan though.
The spurred socket in the loft is protected by a 13amp FCU. Is it still not acceptable to run a spur from that socket to the fan. (It would need another FCU inbetween the socket and fan to fuse it down though).

Oh, and I've thought of something else - if I do run the feed for the fan from an existing lighting junction box, I assume I only need to use 1.5mm 2 core & earth, which will run to the isolator, then to the pullcord, then I will also take the permanent live from the pull cord.

 

[JohnD]

there must be a reason why you don't want to supply it from the lighting circuit. What is this reason?

 

[GaryMo]

Oh, and I've thought of something else - if I do run the feed for the fan from an existing lighting junction box, I assume I only need to use 1.5mm 2 core & earth, which will run to the isolator, then to the pullcord, then I will also take the permanent live from the pull cord.

Don't forget your FCU with a 3A fuse.

 

[pbar]

Oh, and I've thought of something else - if I do run the feed for the fan from an existing lighting junction box, I assume I only need to use 1.5mm 2 core & earth, which will run to the isolator, then to the pullcord, then I will also take the permanent live from the pull cord.

Don't forget your FCU with a 3A fuse.

But I wouldn't need that would I, if the feed is taken from the lighting circuit.

 

[GaryMo]

But I wouldn't need that would I, if the feed is taken from the lighting circuit.

You'll need to read the manufacturers instructions for your chosen fan.

 

[pbar]

But I wouldn't need that would I, if the feed is taken from the lighting circuit.

You'll need to read the manufacturers instructions for your chosen fan.

I see what you mean there, most of them do state to have the fan protected by 3amp. Perhaps they are just being over cautious/protecting themselves, as the norm seems to be to feed the fan from the lighting circuit and have a fan isolating switch.
But I agree that an FCU is better protection.
So, I am going to take the feed from the existing lighting circuit junction box, using 2 core and earth 1.5mm cable. This will then go to a 3amp FCU, then to the pull cord switch, then 3 core and earth 1.5mm will go to the timer fan.

 

[pbar]

The loft socket is a spur yes, so can I not use that then?

No, a spur feeding a socket cannot continue on to feed another spur. .

Is it not right that you can spur from a spur, from a spur, as many times as you wanted. As long as they are all behind one 13amp FCU.

 

[pbar]

So, I am going to take the feed from the existing lighting circuit junction box, using 2 core and earth 1.5mm cable. This will then go to a 3amp FCU, then to the pull cord switch, then from there it will be 3 core and earth 1.5mm to go to the timer fan.

Please could any of you guys confirm that the above is ok, as I'd like to start this but want to make sure it's ok. Cheers.

 

[GaryMo]

Yes, sounds fine.