I've got an overrun timer fan in my bathroom controlled from the
lighting pull-switch.

The builders who installed it (before my time here) put the (non
switched) Fused Unit in the (stud) wall above the bath (ca. 50 cm from
the shower head).

At present if the fuse is removed, the lights work, but the fan doesn't.

I would like to move the fused unit to outside the bathroom, as
recommended in the regs (required?) and replace it with a switched fuse
unit.
I want to be able to override the fan using the switch, but still be
able to use the lights.

All the diagrams I have seen for overrun fan wiring show the FSU in the
supply BEFORE the light and fan.

It doesn't seem logical to have a double-pole FSU going to the fan if
there's a switched live that may still be live even though the FSU is
open circuit.

How should I wire it to get what I want.

Part-P question: since I'm moving wiring OUT of the bathroom I'm
presumably in the clear?

Thanks

Funzbo

Funzbo wrote:
How should I wire it to get what I want.

I asked a similar q here a while ago: here's a good response I got:
http://tinyurl.com/5jmvo. Search the newsgroup archives at
http://tinyurl.com/4qwj8 - this topic comes up all the time!

David

On Sun, 30 Jan 2005 12:46:18 +0000, Funzbo
strung together this:

How should I wire it to get what I want.

I'd be inclined to fit a triple pole fan isolator instead of a
switched spur. This may involve some wiring changes, but the chances
are there is a 3 core and earth that runs through the spur so just
re-route those through the TP switch.

Part-P question: since I'm moving wiring OUT of the bathroom I'm
presumably in the clear?

We're not particularly Part P friendly here, you'll be fine.
--

SJW
Please reply to group or use 'usenet' in email subject

Funzbo wrote:

The builders who installed it (before my time here) put the (non
switched) Fused Unit in the (stud) wall above the bath (ca. 50 cm from
the shower head).

Ohhh nice...

I would like to move the fused unit to outside the bathroom, as
recommended in the regs (required?) and replace it with a switched fuse
unit.

You can have the FCU in the bathroom if you want, preferably in zone 3
though. In addition to the FCU you will need a THREE pole isolator
(hence a FSU is not going to help you in this case)

I want to be able to override the fan using the switch, but still be
able to use the lights.

All the diagrams I have seen for overrun fan wiring show the FSU in the
supply BEFORE the light and fan.

That is fair enough... however the isolator should be between the fan
and all sources of power including the switched live.

It doesn't seem logical to have a double-pole FSU going to the fan if
there's a switched live that may still be live even though the FSU is
open circuit.

Its not... there are three requirements for switching and fusing.
Functional switching, which is provided by the light switch and the
timer in the fan. Isolation, which will need to be provided by a purpose
made three pole isolator (these are available in conventional single
pattress switch form and also as a ceiling mount pull switch), and
fusing, which will need to be provided in the main power connection to
the lighting circuit.

How should I wire it to get what I want.

Personally I would place the three pole isolator in the circuit first,
with a plain FCU (i.e. non switched) FCU after it close to the fan
position. That way you can isolate the FCU as well as the fan should you
need to change the fuse.

Part-P question: since I'm moving wiring OUT of the bathroom I'm
presumably in the clear?

Probably not, since you will need to alter wiring in the bathroom to
effect the change... your call ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

You can have the FCU in the bathroom if you want, preferably in zone 3
though. In addition to the FCU you will need a THREE pole isolator
(hence a FSU is not going to help you in this case)



Its not... there are three requirements for switching and fusing.
Functional switching, which is provided by the light switch and the
timer in the fan. Isolation, which will need to be provided by a purpose
made three pole isolator (these are available in conventional single
pattress switch form and also as a ceiling mount pull switch), and
fusing, which will need to be provided in the main power connection to
the lighting circuit.


How should I wire it to get what I want.


Personally I would place the three pole isolator in the circuit first,
with a plain FCU (i.e. non switched) FCU after it close to the fan
position. That way you can isolate the FCU as well as the fan should you
need to change the fuse.

Thanks All

Ahh, 3 pole isolator. That was what was what I was groping for.

So, is this what you mean?

Supply - FCU - Lights + Pullswitch - 3 pole isolator (ie override for
fan) - Fan

In that earlier post from Stefek ( http://tinyurl.com/5jmvo ), he
suggests that, in this scheme, the FCU is redundant since the lighting
circuit MCB provides that protection.

Or is an FCU a requirement. It would be nice to lose the FCU from above
the shower and just have the isolator switch on the wall outside the
bathroom.


Thanks

Funzbo

In article , Funzbo
wrote:

I've got an overrun timer fan in my bathroom controlled from the
lighting pull-switch.

The builders who installed it (before my time here) put the (non
switched) Fused Unit in the (stud) wall above the bath (ca. 50 cm from
the shower head).

Nasty and dangerous.

At present if the fuse is removed, the lights work, but the fan doesn't.

Even worse. An overrun fan needs 2 live feeds, one via the light switch
to trigger it and another permanent live to power the overrun time. The
FCU will only control one of these, if it's in the switched live the fan
will continue to run for the overrun time if you pull the fuse when the
fan is running with the light on. If it's in the permanent live I would
expect the fan to stop immediately you pull the fuse, or continue to run
until you turn the light off when it would stop immediately without any
overrun. Either way parts of the fan will still be live when the fuse is
removed. In view of the proximity of the bath and shower, take
precautions that the FCU is dry and you are not exposed to any water if
you try this.

I would like to move the fused unit to outside the bathroom, as
recommended in the regs (required?) and replace it with a switched fuse
unit.

Assuming the fan was correctly wired to take it's power from just the
lighting circuit you shouldn't need a FCU, just a 3 pole isolator switch
as others have suggested. This will ensure that the fan can be
completely isolated for maintenance.

I want to be able to override the fan using the switch, but still be
able to use the lights.

A conventional circuit with a 3 pole isolator will enable you to disable
the fan and just use the lights, you won't be able run the fan without
the lights (apart from the overrun time after the lights go out) without
adding a bit more complication.

All the diagrams I have seen for overrun fan wiring show the FSU in the
supply BEFORE the light and fan.

You should only need a FCU if you're powering the fan (and therefore the
light) from a higher rated circuit like the ring circuit.

It doesn't seem logical to have a double-pole FSU going to the fan if
there's a switched live that may still be live even though the FSU is
open circuit.

Neither logical nor safe.

--
Mike Clarke

Funzbo wrote:


In that earlier post from Stefek ( http://tinyurl.com/5jmvo ), he
suggests that, in this scheme, the FCU is redundant since the lighting
circuit MCB provides that protection.

And here he is, saying it again ;-) The F in the FCU isn't doing
anything useful, and as you said yourself we need to isolate *both*
lives and the N for fan maintenance, so it's one pole short of useful
(unlike Ealing, which has at least enough of us... but I digress,
obscurely.)

But you wrote in your earlier posting, 'I want to be able to override
the fan using the switch, but still be able to use the lights'. Not sure
what you mean by 'override' here. If you want only to be able to turn
the fan *off* sometimes, an on-off pullswitch in its permanent-live
would do the business. If you want only to be able to turn it *on*
sometimes independently of the lights, a change-over pullswitch so it
takes its 'trigger' input either from the light's switched-live or from
its perm-live would do the trick - but it seems unlikely to be all that
useful, since you can get the fan to come on and run for the duration of
its run-on timer by flicking the lights on and off. If you want full
three-way control of the fan - 'perm off, comes-on-with-light, perm-on',
you're either into using a single centre-off double-pole toggle-switch
(*please* use one with a plastic paddle, and mount it outside the
bathroom), so that the 'trigger' feeds from either perm-live
("perm-on"), nothing (the centre-off position), or the light's
switched-live ("comes-on-with-light"), or accepting that the isolator's
a perfectly good thing to operate for the 'perm-off' function, leaving
the pullswitch changeover (or a normal 2-way plateswitch mounted outside
the bathroom, or at least in Zone3 or non-zone) to select 'perm on' or
'light-controlled'.

HTH, rather than confuses - Stefek

Stefek Zaba wrote:


But you wrote in your earlier posting, 'I want to be able to override
the fan using the switch, but still be able to use the lights'. Not sure
what you mean by 'override' here. If you want only to be able to turn
the fan *off* sometimes, an on-off pullswitch in its permanent-live
would do the business. If you want only to be able to turn it *on*
sometimes independently of the lights, a change-over pullswitch so it
takes its 'trigger' input either from the light's switched-live or from
its perm-live would do the trick - but it seems unlikely to be all that
useful, since you can get the fan to come on and run for the duration of
its run-on timer by flicking the lights on and off. If you want full
three-way control of the fan - 'perm off, comes-on-with-light, perm-on',
you're either into using a single centre-off double-pole toggle-switch
(*please* use one with a plastic paddle, and mount it outside the
bathroom), so that the 'trigger' feeds from either perm-live
("perm-on"), nothing (the centre-off position), or the light's
switched-live ("comes-on-with-light"), or accepting that the isolator's
a perfectly good thing to operate for the 'perm-off' function, leaving
the pullswitch changeover (or a normal 2-way plateswitch mounted outside
the bathroom, or at least in Zone3 or non-zone) to select 'perm on' or
'light-controlled'.

HTH, rather than confuses - Stefek


Thanks very much - that clarifies enormously.

I'm trying to get it so that the fan can be off during the summer (when
windows are open) and occasionally off in winter (eg when there are lots
of people here using the bathroom for purposes that don't create much
steam).

I hadn't thought of simply sticking a single pole switch in the perm
live to fan.

I suppose it could be a pullswitch with a very short pull, so as not to
be confused with the light.

Then again, I suppose I really should remove the present FCU from above
the bath and replace it with an isolator which isolates N + *both*
Lives. Logical solution would be a 3 pole switch outside the bathroom.
Perhaps marked 'FAN'!

Funzbo

Funzbo wrote:


Then again, I suppose I really should remove the present FCU from above
the bath and replace it with an isolator which isolates N + *both*
Lives. Logical solution would be a 3 pole switch outside the bathroom.
Perhaps marked 'FAN'!

You'll find the usual 'plateswitch'-style 3-pole isolator already says
'FAN' - or has a tasteful Euro-drawing of a 4-blade fan on it. Like this:

http://www.tlc-direct.co.uk/Main_Ind..._CM/index.html

or Screwfix catnum 51728, at
http://www.screwfix.com/app/sfd/cat/...04290&id=51728

Lurch wrote:
.... snipped

I'd be inclined to fit a triple pole fan isolator instead of a
switched spur.
.... snipped

Why does it need to be triple pole? Take the feed to the fan through a
standard 2 pole isolator and then wire from the fan to the switch (and
light, if needed). What am I missing?

--
Dave S
(The return email address is a dummy)

Dave wrote:


Why does it need to be triple pole? Take the feed to the fan through a
standard 2 pole isolator and then wire from the fan to the switch (and
light, if needed). What am I missing?

A fan with a run-on timer has two lives: one is the 'trigger', usually
connected to the bathroom light's switched-live, which tells it to start
running and keep running while that trigger's live. The other is the
permanent live, which lets the fan *keep* running for a
preset/adjustable time - a few minutes, usually - to carry on clearing
the air of pongs and steam after the bathroom light's been turned off
again. The third pole we want to isolate is the neutral, as usual in
double-pole switching. Hence a total of 3 poles - trigger, perm-L, and N
- to be Isolated.

If you run only the perm-L and N through the 'standard 2-pole isolator'
you mention, then the switched-live wire from the '(light, if needed)'
isn't isolated, and while you're working on the fan, A.N.Other Household
Member comes and flicks the light on, livening up proceedings in an
at-once unexpected yet quite predictable fashion...

On Sun, 30 Jan 2005 23:14:22 +0000, Dave
strung together this:

Why does it need to be triple pole? Take the feed to the fan through a
standard 2 pole isolator and then wire from the fan to the switch (and
light, if needed). What am I missing?

The fact that there are three cables, besides the earth, to a fan with
over-run timer. Those being;

Permanent live.
Switched live.
Neutral.

Equals three poles that require isolating.
--

SJW
Please reply to group or use 'usenet' in email subject

In article ,
Dave writes:
Lurch wrote:
... snipped

I'd be inclined to fit a triple pole fan isolator instead of a
switched spur.
... snipped

Why does it need to be triple pole? Take the feed to the fan through a
standard 2 pole isolator and then wire from the fan to the switch (and
light, if needed). What am I missing?

Might be a bit of a bugger servicing the fan if the
isolation switch also disables the bathroom light.

--
Andrew Gabriel

Stefek Zaba wrote:
Dave wrote:


Why does it need to be triple pole? Take the feed to the fan through a
standard 2 pole isolator and then wire from the fan to the switch (and
light, if needed). What am I missing?

.... snipped

If you run only the perm-L and N through the 'standard 2-pole isolator'
you mention, then the switched-live wire from the '(light, if needed)'
isn't isolated, and while you're working on the fan, A.N.Other Household
Member comes and flicks the light on, livening up proceedings in an
at-once unexpected yet quite predictable fashion...


But if you feed the switched L from the permanent L on the fan the whole
lot is isolated by the 2 pole switch to the permanent L (and N) ...
Fans are a pain in the middle of the night so I've got 2 pull-cords, one
for the main light and one for the fan + the light over the shower.


---
Dave S
(The return email address is a dummy)

On Mon, 31 Jan 2005 08:22:06 +0000, Dave
strung together this:

But if you feed the switched L from the permanent L on the fan the whole
lot is isolated by the 2 pole switch to the permanent L (and N) ...
Fans are a pain in the middle of the night so I've got 2 pull-cords, one
for the main light and one for the fan + the light over the shower.

You see, you're moving the goal posts now. A standard fan with no
timer requires 2 pole isolatione, a fan with over-run timer requires 3
poles.

It doesn't matter whether you like them or not. Stop being a troll.
--

SJW
Please reply to group or use 'usenet' in email subject

Dave wrote:

But if you feed the switched L from the permanent L on the fan the whole
lot is isolated by the 2 pole switch to the permanent L (and N) ...

Sorry, I didn't read your earlier post closely enough to realise you
meant running both light and fan downstream of a DP isolator. That'd be
OK from the safety-isolation point of view, but is borderline as far as
convenience goes (both in real life and in the Regs requirement), as it
means you can't use the bathroom light while servicing the fan: a
particular consideration for 'boxed-in', no-window, loos.

I think we've done this topic to death now...

Stefek