Wiring shower extractor fan to shower switch?
Mike Atkinson
going to ask anyway...
I've just fixed an extractor fan into our bathroom for use with a soon
to be fitted shower. I intend to wire this into the lighting circuit
in the normal way - once I can find a 3 pole isolator to fit outside
the bathroom. However, what I'd really like to do if have this fan
switch with the shower rather than the light; the bathroom is already
sufficiently ventilated. Is there any way to do this safely and stay
within the regulations?
Some details: The shower is a 9.5KW unit, so will be wired with 40/45A
cable (I'm getting an electrician in for this as I need a new consumer
unit / RCD / earth bonding etc), presumably switched with a pull cord
just inside the bathroom. The fan unit is an in-duct version with a
variable run-on, so the actual fan wiring connections will be some 2
feet from the inlet sited above the shower (there's also a SELV low
voltage light embedded within the inlet with a transformer supplied to
power this).
So - I have all necessary power supplies and switches to hand. The
feed for the fan will come from the existing loop-in lighting circuit
(which will be moved to a junction box as I'm replacing the existing
bathroom light with a close fitting version which won't support loop-in
connections). The switched live for the fan can come from the light
switch, but is there any way safely use the shower switch? I don't
believe that there exists any pull cord switch that can operate two
independent circuits (do I mean double gang?), so I'd have to tap into
a circuit capable of carrying some 40A. Could a suitable fused
connection be used?
Sorry for rambling on. My guess that this is not possible, as all the
fan units I've seen have been switched from the lighting circuit.
Anyone seen differently?
BTW - I can't recollect seeing a 3 pole isolation switch (as required
to isolate the fan - live, neutral, and the switched live). The RS
components web pages do show a pull cord version (but this is going to
be deleted from the catalogue) but I want a normal rocker switch
version to be sited high up on the wall outside the bathroom. Can
anyone point me in the direction of a supplier? And are these fused
(on both live connections?)?
Thanks for any response.
--
Dr. Michael Atkinson mailto:matk...@abingdon.geoquest.slb.com
GeoQuest Simulation Software Development WWW: http://www.slb.com/
(A division of Schlumberger Evaluation and Production Services (UK) Ltd)
Direct Tel.: +44 (0)1235 543422 Switchboard Tel.: +44 (0)1235 559595
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
Dave Plowman
Mike Atkinson <matk...@abingdon.geoquest.slb.com> wrote:
> Sorry for rambling on. My guess that this is not possible, as all the
> fan units I've seen have been switched from the lighting circuit.
> Anyone seen differently?
It could be done; the snag being that you would have two separate live
supplies to the fan off different circuits from the consumer unit.
I would do it by using a relay, coil fed from the output of the shower
isolator. This would allow the feeds to the fan to come from the lighting
circuit as normal.
> BTW - I can't recollect seeing a 3 pole isolation switch (as required
> to isolate the fan - live, neutral, and the switched live). The RS
> components web pages do show a pull cord version (but this is going to
> be deleted from the catalogue) but I want a normal rocker switch
> version to be sited high up on the wall outside the bathroom. Can
> anyone point me in the direction of a supplier? And are these fused
> (on both live connections?)?
TLC (check FAQ) do two for around a fiver. They are not fused.
--
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Mike Atkinson
>From: Mike Atkinson [mailto:matk...@abingdon.geoquest.slb.com]
>
>BTW - I can't recollect seeing a 3 pole isolation switch (as required
>to isolate the fan - live, neutral, and the switched live). The RS
>components web pages do show a pull cord version (but this is going to
>be deleted from the catalogue) but I want a normal rocker switch
>version to be sited high up on the wall outside the bathroom. Can
>anyone point me in the direction of a supplier? And are these fused
>(on both live connections?)?
>
I know it's bad form, but I'll answer this part myself - the CPC catalogue
has a suitable isolator switch (page 988 if anyone's interested), which'll
do me fine.
Ed Sirett
>fan units I've seen have been switched from the lighting circuit.
>Anyone seen differently?
>
>to isolate the fan - live, neutral, and the switched live). The RS
>components web pages do show a pull cord version (but this is going to
>be deleted from the catalogue) but I want a normal rocker switch
>version to be sited high up on the wall outside the bathroom. Can
>anyone point me in the direction of a supplier? And are these fused
>(on both live connections?)?
>
In principle ths can be done as a simple the fans runs when the shower
supply is on.
All that is needed is a fused switched connection unit wth a 3A fuse and
then then you take the 1.0 sq mm cable to the fan.
In practice there are the following problems.
1) The fused switched connection unit (FSCU) will need to be placed out of
reach (>2.5m high) of anyone using the bath or shower.)
2) The supply cable will be in 10sq mm and a way of jointing this cable is
by using 45A switches. IIRC you would not get two 10mm sq cables into the
terminals of a 45A switch
This means that you will have to tee the 10mm cable using a 100A henley
block (often seen on meter tails for suppling multiple consumer units).
All in all why not simply connect the fan to the lighting circuit, fans with
buolt in humidistats are less than 30GBP and will prevent the room beng
'over ventilated'.
HTH
Ed Sirett
Property Maintainer - North London.
Andy Wade
> I suspect that the answer to the following is a straight "NO",
No, the answer is not no (and thanks for a well set out enquiry).
> However, what I'd really like to do if have this fan
> switch with the shower rather than the light; the bathroom is already
> sufficiently ventilated. Is there any way to do this safely and stay
> within the regulations?
Yes, simple. Forget all about using the lighting circuit and connect the
fan into the shower circuit. Electrically there is no reason not to do
this, provided that you fuse the two live feeds to the fan, and size the
wiring correctly. The additional loading on the shower circuit will of
course be negligible.
I suggest something along the following lines: at your proposed position
for the fan isolator switch install two 1-gang mounting boxes side by side.
From the shower isolator switch run three wires plus earth to your first
box, viz. unswitched live and neutral, and switched live. We'll come on to
sizing these in a moment. For this first box you make up a 'Gridswitch'
[1] assembly consisting simply of two 13A fuse carriers, which you fit with
3A fuses. In the second box goes a regular 3-pole fan isolator (see
below), with the two 'lives' fed in via the fuses in the adjacent box, and
the neutral (and earth) simply looped thro' same. From there you can run a
liberal length of 1mm^2 (or 1.5) triple & earth to the fan.
So in principle, it's simple. In practice, getting the extra wires into
shower isolator pull-switch might prove difficult or impossible if the
shower wiring is 10mm^2, simply due to lack of room in the mounting
pattress. This could be overcome by mounting an adaptable box directly
over the shower isolator and using suitable terminal blocks therein.
Now to the size of wiring from the shower isolator to your 'fusebox'. This
does _not_ need to be 10mm^2, even though it will be protected by a 45A
device. This is because only fault current (i.e. short-circuit) protection
need be considered. (The 3A fuses downstream will provide the necessary
overload protection.) In general, to calculate the cable size needed here
you need to know the characteristics of the supply-side fuse or breaker,
and the fault current. You then use the 'adiabatic equation' to check that
the device will protect the cable and not the other way round. Help, this
is getting technical, you may think... However, in your case you mentioned
a new consumer unit. If we can assume that the shower circuit is protected
by a 45A Type B MCB, and that the shower circuit itself complies with the
regulations, then it can be shown that you will be perfectly OK using
1.5mm^2 triple & earth straight off the shower circuit. The other proviso
is that this 'stub' is kept fairly short, say 2m max. If it's too long the
fault current is lowered, and the MCB may not trip quickly enough. For the
avoidance of any doubt I must stress that this sizing holds ONLY for the
45A Type B MCB. If the shower circuit uses a fuse, a larger cable size,
and a calculation, will almost certainly be needed.
> BTW - I can't recollect seeing a 3 pole isolation switch
This is a readily available item that you can get from any wholesaler. MK
and Crabtree certainly make them, and probably several others. Unfused,
with a single-gang white faceplate.
[1] Gridswitch is actually a registered trademark of MK, but I use it here
in a generic sense.
HTH
--
Andy
Andrew Gabriel
"Andy Wade" <ajw...@dial.pipex.com> writes:
>
>Yes, simple. Forget all about using the lighting circuit and connect the
>fan into the shower circuit. Electrically there is no reason not to do
>this, provided that you fuse the two live feeds to the fan, and size the
>wiring correctly. The additional loading on the shower circuit will of
>course be negligible.
>
>I suggest something along the following lines: at your proposed position
>for the fan isolator switch install two 1-gang mounting boxes side by side.
> From the shower isolator switch run three wires plus earth to your first
>box, viz. unswitched live and neutral, and switched live.
Andy, the problem here is that the fan is now bridging the
live side of the shower isolating switch. OK, it's not going
to let through enough current for the shower (or a bathroom
lamp to light), but it has broken the function of the isolator.
--
Andrew Gabriel
Consultant Software Engineer
Dave Plowman
Andy Wade <ajw...@dial.pipex.com> wrote:
> Yes, simple. Forget all about using the lighting circuit and connect the
> fan into the shower circuit. Electrically there is no reason not to do
> this, provided that you fuse the two live feeds to the fan, and size the
> wiring correctly. The additional loading on the shower circuit will of
> course be negligible
<snip>
What a performance and cost. If you wire a 240 v relay across the output
of the shower isolator, the normally open contacts can be treated as an
ordinary light switch as far as the fan is concerned. Such a relay costs
around a fiver from the likes of Maplin, and fits easily in a one gang box.
Deano
<matk...@abingdon.geoquest.slb.com> wrote:
>
> going to ask anyway...
> BTW - I can't recollect seeing a 3 pole isolation switch (as required
> to isolate the fan - live, neutral, and the switched live)
comtactum sell the switches.
enquire at you'r local trade center.
poped into rex in chandlers ford.
nice big center...
beter than the sheads.
Tim
--
--
td...@argonet.co.uk.co http://www.argonet.co.uk/users/tdean
..Internet access for all Acorn RISC machines td...@argonet.co.uk
Suporter of Bring back buffy to terrestial tv
http://buffy.acmecity.com/cordelia/98/campaign.html
Oh I am 18 29/08.
... I forgot my tagline file...
Andy Wade
> Andy, the problem here is that the fan is now bridging the
> live side of the shower isolating switch. OK, it's not going
> to let through enough current for the shower (or a bathroom
> lamp to light), but it has broken the function of the isolator.
Yes, that occurred to me too, just after I posted that reply. Not quite
so simple after all, but still not insoluble. A three-pole shower
isolator would do the trick, but isn't something you'd want on show in
your bathroom or landing! As someone else suggested you could use a relay
(coil across outgoing side of shower isolator, single SPNO contact between
L and switched L of fan) in which case the fan could go back on the
lighting circuit. Ho hum...
--
Andy
Mike Atkinson
>From: Dave Plowman [mailto:dave....@argonet.co.uk]
>
> What a performance and cost. If you wire a 240 v relay across the output
>of the shower isolator, the normally open contacts can be treated as an
>ordinary light switch as far as the fan is concerned. Such a relay costs
>around a fiver from the likes of Maplin, and fits easily in a one gang box.
>
Dave - many thanks to you and all the other respondents.
The replies so far all say that there are solutions to my problem, but yours
seems the least 'invasive' to the shower circuit. Nobody, I think, has
commented on whether the regulations allow connections to/across the shower
isolator.
Could I question you regarding the relay solution. My knowledge of relays
is from my schooldays, so I'm on dodgy ground here! By 'coil fed from the
output of the shower isolator' (your original reply) are you saying that the
secondary circuit is switched on detecting current flow in the shower
circuit by way of the switched live shower feed passing through a coil in
the relay? My concern would be about heat generation, but I guess if the
relay is adequately rated this wouldn't be an issue.
I've had a quick dive around in the Maplin web site (now up and running).
The relays I've seen there, and elsewhere, are all the PCB mounting type
(mostly switching mains current as a result of an applied low voltage); is
this what you're suggesting, or is there a relay designed for this purpose
that I'm missing?
Mungo Henning
Mike Atkinson wrote:
> Dave - many thanks to you and all the other respondents.
>
> The replies so far all say that there are solutions to my problem, but yours
> seems the least 'invasive' to the shower circuit.
I guess you have discounted the excellent suggestion by Ed Sirett regarding
fitting a humidity-sensed extractor fan? If the purpose of the fan is to
reduce condensation, this ought to be given more consideration.
How's about another suggestion: wire the fan off the lighting circuit and use
a momentary press-to-make switch to trip the fan? (the "moment" might be
five seconds if its anything like the fan I bought :-)
Set the fan's overrun timer to be (say) half an hour and educate the users
to when it ought to be used?
>
>
> Could I question you regarding the relay solution. My knowledge of relays
> is from my schooldays, so I'm on dodgy ground here! By 'coil fed from the
> output of the shower isolator' (your original reply) are you saying that the
> secondary circuit is switched on detecting current flow in the shower
> circuit by way of the switched live shower feed passing through a coil in
> the relay? My concern would be about heat generation, but I guess if the
> relay is adequately rated this wouldn't be an issue.
Nope. The relay isn't wired in series with the shower, it is wired in parallel
with it. Mains rated relays are available; Maplin isn't always the cheapest
Mungo
--
Mungo Henning - it's a daft name but it goes with the face...
mungoh@itacs.strath.ac.uk.http://www.itacs.strath.ac.uk/
I speak for me, not my employer.
Dave Plowman
Mike Atkinson <matk...@abingdon.geoquest.slb.com> wrote:
> I've had a quick dive around in the Maplin web site (now up and
> running). The relays I've seen there, and elsewhere, are all the PCB
> mounting type (mostly switching mains current as a result of an applied
> low voltage); is this what you're suggesting, or is there a relay
> designed for this purpose that I'm missing?
The one I would use is part no FX 49. It has *two* sets of contacts which
change over, like a double pole two way switch. They are rated at 7.5 amp
at 250v AC, and it has a life of around 20 million operations.;-) Cost
5.45 ukp. They are suitable for continuous use, and I have never known one
to fail, unless overloaded, which is impossible in this case. They make a
very satisfying 'thunk' when switched on, although if you mount it inside
the ceiling, it won't be noticed.
It has a threaded mounting hole, and should be fixed on its side inside a
one gang metal box, with a lid. A 75x75x50mm 'adaptable' box with
knockouts from your local wholesaler would be ideal. I suppose it should
be fused, but I wouldn't bother, as even if the coil did short, there is
little danger of it overloading the wiring.;-) You will need to make
solder connections to the coil and the required contacts (two) and bring
them out to a connector strip within the box. You can then treat it like
the light switch which would normally feed the fan.
Once you get you head round the principle of relays they open up all sorts
of oppertunities. You need an intermediate switch but only a two way is
available in the style you want? A relay will sort it.
Light or appliance switches *inside* the bathroom? Low voltage relays
with an appropriate power supply would allow you to have a light switch
you can *operate* from the bath.
Andy Wade
> I've had a quick dive around in the Maplin web site (now up and running).
> The relays I've seen there, and elsewhere, are all the PCB mounting type
> (mostly switching mains current as a result of an applied low voltage);
is
> this what you're suggesting, or is there a relay designed for this
purpose
> that I'm missing?
Yes, you can buy plug-in mains relays which have 8- or 11-pin bases. The
8-pin type usually have 2 changeover contacts (DPCO) and the 11-pin have 3
[ditto]. As you only need a single 'make' contact the 8-pin type is what
you need, with a 230V or 240V rated coil. You can also buy a base with
screw terminals for the relay to plug in to, so no soldering is necessary.
Mount the relay base in a suitable adaptable box, and take care to maintain
good clearance between the shower and lighting circuits (6mm minimum
clearance advised, but much more should be achievable).
Such relays are available from RS, Farnell, CPC, etc. and I'd be very
surprised if the 'etc.' didn't include Maplin.
--
Andy
Mike Atkinson
>From: Mungo Henning [mailto:mun...@itacs.strath.ac.uk]
>I guess you have discounted the excellent suggestion by Ed Sirett regarding
>fitting a humidity-sensed extractor fan? If the purpose of the fan is to
>reduce condensation, this ought to be given more consideration.
>
Unfortunately I already have a non humidity sensing fan half fitted; just
the wiring to do. I believe that you can get the sensors separately, but no
doubt these cost more than a fan with such a sensor fitted.
>How's about another suggestion: wire the fan off the lighting
>circuit and use
>a momentary press-to-make switch to trip the fan? (the "moment" might be
>five seconds if its anything like the fan I bought :-)
>
Yes - I'd thought of that, and haven't totally discounted it. My old house
(which was new, if you see what I mean) was wired 'both' ways; the fan came
on with the light, but could also be triggered by a pull cord. The downside
of this was that there were *three* pull cords just inside the bathroom
door.
Here's a thought. I may put a press-to-make switch outside the bathroom
(alongside the isolator perhaps; it'd be nice to combine the two with a two
way 3p isolator, but I doubt if these exist) and have a humidity sensor
inside. I need to have another dig around what's available...
>> By 'coil fed from the output of the shower isolator' (your original
>> reply) are you saying that the
>> secondary circuit is switched on detecting current flow in the shower
>> circuit by way of the switched live shower feed passing through a coil
>> in the relay?
>Nope. The relay isn't wired in series with the shower, it is wired
>in parallel
>with it. Mains rated relays are available; Maplin isn't always the cheapest
>
In parallel with the switched live lead, or actually across the isolator
itself? And yes, I've seen mains rated relays, but can they cope with 10
mm^2 flex connections? The ones I've seen can switch up to 10A, but don't
state the maximum 'input' (prob. the wrong word) current. I need to do some
reading...
>Mungo Henning - it's a daft name but it goes with the face...
I have to say, I've always thought this as the best sig I've seen. From
where does Mungo originate? IIRC there's a character in Blazing Saddles
called Mungo, not that you'll thank me for that!
Ed Sirett
Mungo Henning wrote in message <37CD1CF3...@itacs.strath.ac.uk>...
>
>
>I guess you have discounted the excellent suggestion by Ed Sirett regarding
>fitting a humidity-sensed extractor fan? If the purpose of the fan is to
>reduce condensation, this ought to be given more consideration.
>
>How's about another suggestion: wire the fan off the lighting circuit and
use
>a momentary press-to-make switch to trip the fan? (the "moment" might be
>five seconds if its anything like the fan I bought :-)
>
>Set the fan's overrun timer to be (say) half an hour and educate the users
>to when it ought to be used?
>
Did this about 3 months ago for a toilet room where the window was difficult
to access.
The switch came with the word 'press' engraved on it so everyone (I'm told)
uses it ;-)
The switch has to be held in for about half a second (i.e. a deliberate
press rather than a quick dab).
Deano
Rex at chandlers ford has been moved round the back of the old building.
it is bigger and better.
and the drinks machien workes :-)
better service than at b+q
tim
Dave Plowman
Mike Atkinson <matk...@abingdon.geoquest.slb.com> wrote:
> In parallel with the switched live lead, or actually across the isolator
> itself? And yes, I've seen mains rated relays, but can they cope with
> 10 mm^2 flex connections? The ones I've seen can switch up to 10A, but
> don't state the maximum 'input' (prob. the wrong word) current. I need
> to do some reading...
The relay coil is wired to the same two terminals as the shower, so it
operates with it. You don't need to run 10mm cable to it; it only draws a
few milliamps. 1 mm lighting cable will be more than adequate. I suppose
it might be worth incorporating a small fuse close to the shower switch,
as the only protection for the 1 mm cable would be the shower fuse or MCB,
and this would not protect the smaller cable on a long run if a fault
developed.
Chris French
<dave....@argonet.co.uk> writes
>
> Light or appliance switches *inside* the bathroom? Low voltage relays
>with an appropriate power supply would allow you to have a light switch
>you can *operate* from the bath.
>
thinking..... :-)
--
Chris French, Leeds
Andrew Gabriel
"Mike Atkinson" <matk...@abingdon.geoquest.slb.com> writes:
>
>The replies so far all say that there are solutions to my problem, but yours
>commented on whether the regulations allow connections to/across the shower
>isolator.
They don't allow such connections.
There is likely to be a semi-conductor connection between the
two live feeds to a fan, and the regs explicitly forbid using
a semi-conductor as an isolator, which is in effect what you
would then have.
Andy Wade
> "Mike Atkinson" writes:
> >
> > Nobody, I think, has
> > commented on whether the regulations allow connections to/across the
> > shower isolator.
>
> They don't allow such connections.
> There is likely to be a semi-conductor connection between the
> two live feeds to a fan, and the regs explicitly forbid using
> a semi-conductor as an isolator, which is in effect what you
> would then have.
We seem to be losing the thread here. That comment seems to refer to my
original response, which I'd be the first to agree was ill-considered and
should be ignored. What Mike was referring to though was Dave Plowman's
idea of using a relay. I can see no objection to that, provided that a
suitable relay is chosen and that the wiring to it maintains electrical
separation between the shower feed to the coil and the fan circuit side.
The relay 'control box' that needs to be made-up here should carry a label
to the effect that both the shower and the fan (lighting) circuits need to
be isolated in order to render the box dead (reg. 461-01-03).
In other words, the answer to Mike's question is that there is nothing to
prevent 'other connections' being made to the terminals of the shower
isolator, _provided_ that nothing is done which bridges the isolation.
Also, any such connections must be adequately sized so as to be
short-circuit protected, bearing in mind the 45A circuit. As I said
before though, _provided_ that the 45A device is a Type B MCB (and that
the shower circuit is otherwise compliant) then 1.5mm^2 (and even 1.0mm^2
in fact) will be OK, subject also to the length being kept short. I would
also recommend putting a 20mm 1A HBC fuse in series with the relay coil,
inside the control box.
--
Andy
Mike Atkinson
>The relay coil is wired to the same two terminals as the shower, so it
>operates with it. You don't need to run 10mm cable to it; it only draws a
>few milliamps. 1 mm lighting cable will be more than adequate. I suppose
>it might be worth incorporating a small fuse close to the shower switch,
>as the only protection for the 1 mm cable would be the shower fuse or MCB,
>and this would not protect the smaller cable on a long run if a fault
>developed.
>
Dave - many thanks for your clarification. I think my addled brain now
understands this. My rough calculations (assuming 230V supply, 9.5KW
shower, 7300Ohm relay) shows that the relay wired in parallel with the
shower draws some 30mA compared with 41A for the shower. I do think I'll
add a fuse carrier to the relay circuit though.
So I think I'll go with this. The fan will be effectively on the light
circuit, and isolated via a 3p switch. I may (as it's so simple) add a
momentary push-to-close switch next to the isolator to allow the fan to be
triggered independently of switching the shower on.
My only concern now is Andrew Gabriel's posting to the effect that even this
relay link breaks regulations.
Mike Atkinson
>From: Andrew Gabriel [mailto:and...@cucumber.demon.co.uk]
>Sent: 01 September 1999 22:49
>They don't allow such connections.
>There is likely to be a semi-conductor connection between the
>two live feeds to a fan, and the regs explicitly forbid using
>a semi-conductor as an isolator, which is in effect what you
>would then have.
>
Andrew - thanks for the response.
I had suspected that the regs. might have something to say on this matter.
However, can I just clarify this :- what is being proposed is that the
shower and the relay (triggering the fan on the lighting circuit) would be
wired in parallel on the isolated side of the shower isolator. The shower
supply circuit will be open when isolated. Where I think there may be a
difficulty is that that fan circuit will still be live, with a live lead
going to the relay 'close' to the shower circuit. Is this the problem as
far as the regs. are concerned?
Dave Plowman
Mike Atkinson <matk...@abingdon.geoquest.slb.com> wrote:
> My only concern now is Andrew Gabriel's posting to the effect that even
> this relay link breaks regulations.
I *think* Andrew is referring to direct connection of the fan 'sensing'
feed to the shower isolator. The relay gets round this. My only concern
when recommending the relay approach is the protection of the cable
feeding it when the only 'fuse' is 45 amp. Andy Wade seems to think a
short length of 1mm would be ok; I would therefore site the relay as close
to the isolator as possible.
Andrew Gabriel
Dave Plowman <dave....@argonet.co.uk> writes:
>In article <005901bef519$758858d0$a892...@abingdon.geoquest.slb.com>,
> Mike Atkinson <matk...@abingdon.geoquest.slb.com> wrote:
>> My only concern now is Andrew Gabriel's posting to the effect that even
>> this relay link breaks regulations.
>
>I *think* Andrew is referring to direct connection of the fan 'sensing'
>feed to the shower isolator.
Indeed I was. This thread got confusing, in part at least
due to me. Whoops, sorry... :-)
Andy Wade
> My only concern
> when recommending the relay approach is the protection of the cable
> feeding it when the only 'fuse' is 45 amp. Andy Wade seems to think a
> short length of 1mm would be ok
Yes it will, but let me stress again, ONLY if the 'fuse' is a Type B MCB.
If the 'fuse' was a 45A re-wireable fuse then the wiring would protect the
fuse, possibly starting a fire in the process.
Take care, incidentally when connecting large and small wires together into
the same terminal. It's sometimes tricky to get them both to connect
securely, and the shower isolator is a place where (a) room is tight, and
(b) you don't want any risk of a loose connection.
--
Andy
Mike Atkinson
>From: Andy Wade [mailto:ajw...@dial.pipex.com]
>Sent: 03 September 1999 13:25
>
>Dave Plowman wrote ...
>
>> My only concern
>> when recommending the relay approach is the protection of the cable
>> feeding it when the only 'fuse' is 45 amp. Andy Wade seems to think a
>> short length of 1mm would be ok
>
>Yes it will, but let me stress again, ONLY if the 'fuse' is a Type B MCB.
>If the 'fuse' was a 45A re-wireable fuse then the wiring would protect the
>fuse, possibly starting a fire in the process.
I will add a fuse (3A?) in-line with the relay coil, which should hopefully
provide sufficient protection. The 45A fuse in the consumer unit certainly
won't be re-wireable...
As I stated at the beginning of this thread I'm getting an electrician into
wire the shower circuit, as I need a new consumer unit, earth bonding, and
haven't any experience with 10 mm^2 cable. (I also have little time - one 2
yr old and another one on the way). The new consumer unit will have MCB and
some RCDs; I need to discuss this with the electrician when I get a quote.
>Take care, incidentally when connecting large and small wires together into
>the same terminal. It's sometimes tricky to get them both to connect
>securely, and the shower isolator is a place where (a) room is tight, and
>(b) you don't want any risk of a loose connection.
Yes - I'm already beginning to imagine the scenario when I try to persuade
the electrician that it's OK to attach two 1.5 mm^2 wires leading to a
suspicious box to his newly installed 45A isolation switch.
Andy Wade
> I will add a fuse (3A?) in-line with the relay coil, which should
hopefully
> provide sufficient protection. The 45A fuse in the consumer unit
certainly
> won't be re-wireable...
The 3A fuse will only protect the wiring in the relay box (in the event
that the relay coil develops shorted turns, etc.). It won't protect the
wiring which comes before it, which must therefore be coordinated with the
45A device. If the latter ends up being a BS1361 cartridge fuse, rather
than the MCB, you'd need 2.5mm^2 (including earth) to the relay box.
> Yes - I'm already beginning to imagine the scenario when I try to
persuade
> the electrician that it's OK to attach two 1.5 mm^2 wires leading to a
> suspicious box to his newly installed 45A isolation switch.
Point them to regulation 473-02-03, which is what is being applied here.
--
Andy