'Slow-blow' MCBs?
nick nelson
Having recently replaced my old fuse box with a modern
CU and MCBs, the only problem seems to be that the 6A
lighting circuit always trips when a bulb blows, plunging
the whole house into darkness.
Is there such a thing as a 'slow blow' equivalent in MCBs?
I had a look in the TLC catalogue but couldn't see anything.
Nick.
Andrew Gabriel
In article <341FFF...@education.leeds.ac.uk>,
Yes, MCBs are available in a variety of ratings. There are
two rating schemes, the old UK one (Types 1, 2, 3, 4) and
the new EU one (Types B, C, D). The 'normal' ratings are
Type 2 or Type B (they don't match exactly). A Type 3 or
Type C would be a 'slow blow' one, typically used for large
motors (but not large enough to have soft-start). Type D
or Type 4 are 'very slow blow' but need special wiring
(because normally rated wiring could be damaged by over-
heating before the MCB trips) and you wouldn't ever find
type D or Type 4 in domestic situations. There is also a
'fast blow' Type 1 (there is no corresponding Type A) -
you could make sure you havn't got a Type 1 on your lighting
circuit.
I suspect that if you've got a Type 2 or Type B, your
particular sample is rather over enthusiastic. Personally,
I would change it to another Type 2 or Type B before trying
a Type 3 or Type C. Also, you do buy filament lamps with
fuses in them I presume? (I've never seen any without in
this country, but there might be some cheap imports like this).
--
Andrew Gabriel And...@cucumber.demon.co.uk
Consultant Software Engineer
Keith Mendum
nick nelson wrote:
>
> Is there such a thing as a 'slow blow' equivalent in MCBs?
> I had a look in the TLC catalogue but couldn't see anything.
>
Type B MCBs, but Type C ones are also available, although they cost a
little more. MEM certainly do type C, and I would be surprised if MK and
Crabtree did not also do them.
The difference is that type B trip instantaneously at 3-5 x normal rated
current, whereas type C trip instantaneously at 5-10 x normal rated
current.
--
Keith Mendum
My views, not Nortels'.
nick nelson
Keith Mendum wrote:
> Yes, there are 'slow blow' MCBs. Most domestic consumer unit come with
> Type B MCBs, but Type C ones are also available, although they cost a
> little more. MEM certainly do type C, and I would be surprised if MK and
> Crabtree did not also do them.
>
> The difference is that type B trip instantaneously at 3-5 x normal rated
> current, whereas type C trip instantaneously at 5-10 x normal rated
> current.
Thanks for this. I hadn't realised that there was this much variation
between units. As Andrew G. has pointed out, I may just have an overly
sensitive example.
Nick.
Charles (Joe) Stahelin
In article <5vohus$1...@cucumber.demon.co.uk>, Andrew Gabriel
<and...@cucumber.demon.co.uk> writes
>Also, you do buy filament lamps with
>fuses in them I presume? (I've never seen any without in
>this country, but there might be some cheap imports like this).
That is news ! Please tell us a little more.
--
Charles (Joe) Stahelin
Huddersfield, West Yorkshire, UK
a.re...@virgin.net
I use GEC bulbs with a ballatini fuse and mine still blow all the time in
the seven self catering holiday apartments I built. (Hagar MCB's seem
more prone than Wylex !)
I think I need the slow MCBs or I may go back to fuses on the lighting
circuit! How slow are fuses compared to a slower MCB ?? Anyone know ?
- Andrew
Keith Mendum wrote:
>
> nick nelson wrote:
> >
> > Is there such a thing as a 'slow blow' equivalent in MCBs?
> > I had a look in the TLC catalogue but couldn't see anything.
> >
> Yes, there are 'slow blow' MCBs. Most domestic consumer unit come with
> Type B MCBs, but Type C ones are also available, although they cost a
> little more. MEM certainly do type C, and I would be surprised if MK and
> Crabtree did not also do them.
>
> The difference is that type B trip instantaneously at 3-5 x normal rated
> current, whereas type C trip instantaneously at 5-10 x normal rated
> current.
>
Chris Holmes
Andrew Gabriel <and...@cucumber.demon.co.uk> wrote in article
<5vohus$1...@cucumber.demon.co.uk>...
> Also, you do buy filament lamps with
> fuses in them I presume? (I've never seen any without in
> this country, but there might be some cheap imports like this).
>
Que?
I've never noticed a fuse in any of my lamps. Are we talking about light
bulbs here? Where is the fuse? Does it say on the box that they're fused?
Which country are you in?
And aside of "better than a man" (except when it comes to D.I.Y), what is
cucumber?
Keith Mendum
a.re...@virgin.net wrote:
> I think I need the slow MCBs or I may go back to fuses on the lighting
> circuit! How slow are fuses compared to a slower MCB ?? Anyone know ?
>
they _should_ blow faster than type B MCBs. These are a faily recent
spec for MCBs and older domestic MCBs may be type 2 or even type 1, both
of which are more susceptible to overload than type B. Type T, slowblow,
fuses are NOT recommended for domestic consumer units.
Rewirables are a law unto themselves, avoid at all costs!
John Laird
In article <01bcc4ed$702caac0$823d...@netman.sedgehill.lewisham.sch.uk>, "Chris Holmes" <hol...@sedgehill.lewisham.sch.uk> writes:
> Andrew Gabriel <and...@cucumber.demon.co.uk> wrote in article
> <5vohus$1...@cucumber.demon.co.uk>...
>> Also, you do buy filament lamps with
>> fuses in them I presume? (I've never seen any without in
>> this country, but there might be some cheap imports like this).
>>
>
> Que?
>
> I've never noticed a fuse in any of my lamps. Are we talking about light
> bulbs here? Where is the fuse? Does it say on the box that they're fused?
>
Nevertheless, I suffer frequent 6A MCB trips when a bulb goes. It's the down
side of capitalism that such a thing as a light-bulb is still such crap as
we near the 21st entry - only the profit motive could have held up the
development of something better/cheaper/more reliable.
> Which country are you in?
>
> And aside of "better than a man" (except when it comes to D.I.Y), what is
> cucumber?
>
Why so many questions ? ;-)
--
John Laird (jo...@yrl.co.uk) "I have discovered a truly elegant sig,
Yezerski Roper Ltd sadly there is no room here to show it."
http://www.yrl.co.uk
Andrew Gabriel
In article <01bcc4ed$702caac0$823d...@netman.sedgehill.lewisham.sch.uk>,
"Chris Holmes" <hol...@sedgehill.lewisham.sch.uk> writes:
>
>I've never noticed a fuse in any of my lamps. Are we talking about light
>bulbs here? Where is the fuse?
The fuse is in the supply wires where they go up the centre of the
bulb, before passing through the glass into the partial vacuum.
The fuse is either simply a thinning of the wire, or a ballotini
fuse consisting of a thinning of the wire encased in a sealed glass
tube which is packed with small glass spheres (ballotini are actually
the small glass spheres). I guess the ballotini are there to safely
absorb the molton metal (where it might otherwise crack/shatter the
bulb glass) and/or more rapidly quench any arc, but I've never actually
found out their purpose for sure.
>Does it say on the box that they're fused?
No, but as I said, I've never seen any in this country which weren't,
whereas I know there have been some available in the US which weren't.
I suspect they are required by the relevant British Standard.
>
>Which country are you in?
>
>And aside of "better than a man" (except when it comes to D.I.Y), what is
>cucumber?
Which planet are you on? :-)
Andrew Gabriel
In article <XoyPHW7V+y$$@yrl.co.uk>,
jo...@yrl.co.uk (John Laird) writes:
>It's the down
>side of capitalism that such a thing as a light-bulb is still such crap as
>we near the 21st entry - only the profit motive could have held up the
>development of something better/cheaper/more reliable.
Like a compact fluorescent; better, cheaper, and more reliable
(and possibly only available in capitalist countries :-) ).
Ian M. Stewart
a.re...@virgin.net wrote:
>I use GEC bulbs with a ballatini fuse and mine still blow all the time in
>the seven self catering holiday apartments I built. (Hagar MCB's seem
>more prone than Wylex !)
>
>I think I need the slow MCBs or I may go back to fuses on the lighting
>circuit! How slow are fuses compared to a slower MCB ?? Anyone know ?
I have vague memories of the re-wireable fuse taking *five minutes*
to blow at 2x the rated current. Doesn't bear thinking about, does
it? Cartridge fuses are better - but not by much. Stick to MCBs.
--
Ian <IMS>
Traffic engineering : Order out of chaos....
i...@wavenet.co.uk
Andrew Gabriel
In article <342427ee...@news1.wavenet.co.uk>,
i...@post1.wavenet.co.uk (Ian M. Stewart) writes:
>
>I have vague memories of the re-wireable fuse taking *five minutes*
>to blow at 2x the rated current. Doesn't bear thinking about, does
>it? Cartridge fuses are better - but not by much. Stick to MCBs.
This figure is also just within permitted range for a 6A Type 2 MCB.
To guarantee tripping within 1 second, you need up to 7x the rated
current (depends on sample, some might only require 4x rated current).
The MCB is designed to protect the wiring from overheating, and
wiring will survive overcurrent for short periods (inversely
related to the overcurrent) without overheating, hence the MCB's
behaviour.
John Laird
In article <5vuln8$k...@cucumber.demon.co.uk>, and...@cucumber.demon.co.uk (Andrew Gabriel) writes:
> In article <XoyPHW7V+y$$@yrl.co.uk>,
> jo...@yrl.co.uk (John Laird) writes:
>
>>It's the down
>>side of capitalism that such a thing as a light-bulb is still such crap as
>>we near the 21st entry - only the profit motive could have held up the
>>development of something better/cheaper/more reliable.
>
> Like a compact fluorescent; better, cheaper, and more reliable
> (and possibly only available in capitalist countries :-) ).
>
sets of fittings in our house where they either wouldn't physically fit, or
would look awful, or couldn't be dimmed. My point was simply this: do
conventional filament bulbs have to be quite _so_ poor ?
Matthew Marks
If you look carefully you can see it in one of the leadout wires. Why is it
there, when a bit of broken filament is so thin that it couldn't offer such
a low resistence? Because sometimes when the bulb fails, the resulting arc
ionises the inert gas, and causes a very low resistance plasma discharge.
Why is the bulb filled with gas instead of containing a vacuum? Because it
decreases the rate of evaporation of the filament, and hence increases bulb
life.
--
Matthew @rd.bbc.co.uk My opinions, not Auntie's *RETURN ADDRESS SPAMPROOFED*
nightjar
John Laird <jo...@yrl.co.uk> wrote in article <+ILb$G+8...@yrl.co.uk>...
>
> Well I wasn't unaware of these, Andrew, but... I could reel off about 6
> sets of fittings in our house where they either wouldn't physically fit,
or
> would look awful, or couldn't be dimmed. My point was simply this: do
> conventional filament bulbs have to be quite _so_ poor ?
No, you can use the type made for difficult areas, like a light fitting in
the ceiling of a long escalator in the London Underground. Sold under names
like '10-year light bulb' they have expected lives of around 10,000 hours,
instead of the normal 1,000-2,000 hours. The trade-off is that you cannot
get long life and the same light output per watt, so the are about 80% of
the brightness of a standard bulb of the same power consumption.
Nightjar
Keith Mendum
a.re...@virgin.net wrote:
>
> Andrew Renouf wrote:-
>
> I have put the Hagar cartridge fuses (on the lighting circuit only) in my
> own house and these have never blown one !
This is exactly what you should expect if the bulb is smaller than about
500W.
> I think there is more risk from somebody killing themself in an
> unfamiliar holiday apartment walking around in the dark than any
> increased protection from a MCB !
>
Quite so! Under normal circumstances and with no fooling around, there
is little risk from a lighting circuit with the correctly rated
protective device fitted. The choice of device is often one of
convenience, so provide a spare fuse, possibly ready fitted to a
carrier.
a.re...@virgin.net
Andrew Renouf wrote:-
Thanks for the posting keith, I have 8 self catering apartments and the
6 amp MCB's often trip on lightbulb failure- I'm going to look this
weekend when the holiday makers move out but I'm sure they are all type
B.
(I use GEC lamps with a balatini fuse and the lighting circuits are split
into 2 so are not operating anywhere close to 6 amps even if every light
is on !)
I have put the Hagar cartridge fuses (on the lighting circuit only) in my
own house and these have never blown one !
I think there is more risk from somebody killing themself in an
unfamiliar holiday apartment walking around in the dark than any
increased protection from a MCB !
What do you think ? - Andrew
Keith Mendum wrote:
> Most cartridge fuses in consumer units etc are type F, quickblow and
> they _should_ blow faster than type B MCBs. These are a faily recent
> spec for MCBs and older domestic MCBs may be type 2 or even type 1, both
> of which are more susceptible to overload than type B. Type T, slowblow,
> fuses are NOT recommended for domestic consumer units.
>
> Rewirables are a law unto themselves, avoid at all costs!
a.re...@virgin.net
Andrew Renouf replied to Keiths's comment below-
> Quite so! Under normal circumstances and with no fooling around, there
> is little risk from a lighting circuit with the correctly rated
> protective device fitted. The choice of device is often one of
> convenience, so provide a spare fuse, possibly ready fitted to a
> carrier.
Well Keith, thanks for backing me up here ! - The hagar board has MCB
size fuse carriers which take a standard plugtop cartridge fuse. This is
really handy as anybody can change it !
- Andrew