In uk.transport.london message , Mon, 14
Apr 2008 14:10:17, funkmish posted:
Andy Burns wrote:
On 11/04/2008 12:23, funkmish wrote:

Four regular 40w lamps wired in parallel should do the trick. The
problem comes when one of them blows
Four 240V lamps wired in parallel across a 750V supply would blow
rather quickly I'd expect. You should try to explain that you meant
to say "in series" at this point ;-)

Yes, I meant in series, hence my comment about when one of them blows!

When one blows, the full voltage will appear across it and its socket;
that is undoubtedly more that their designers expected them to receive,
and may be more than they can reliably stand, especially in an
environment which may be damp or mucky.

I am reminded that I once inherited an equipment which included a 3 kV
DC supply charging a cubic metre or so of capacitors via a couple of
dozen ordinary 200 V bulbs in series and an ordinary 1.25" cartridge
fuse and holder. One day, the fuse blew. The current continued, only
slightly impeded, until the burning fuse holder disintegrated.

--
(c) John Stockton, nr London UK.
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
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On Mon, 14 Apr 2008 23:07:44 +0100 someone who may be Dr J R
Stockton wrote this:-

an ordinary 1.25" cartridge fuse

What's one of those?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article ,
David Hansen wrote:
On Mon, 14 Apr 2008 23:07:44 +0100 someone who may be Dr J R
Stockton wrote this:-

an ordinary 1.25" cartridge fuse

What's one of those?

CPC part number: FS01458 etc.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

On Tue, 15 Apr 2008 08:55:31 +0100 someone who may be charles
wrote this:-

an ordinary 1.25" cartridge fuse

What's one of those?

CPC part number: FS01458 etc.

http://cpc.farnell.com says there is no such part.

To be of any use to people the OP should have given some useful
information, such as the current rating and (perhaps) the breaking
capacity of the fuse. The physical sizes of fuses are not useful.

If the intention was to be a little more coy then whether the
dimension quoted was the length or diameter would have been useful.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On 15/04/2008 09:44, David Hansen wrote:

The physical sizes of fuses are not useful.

Sounds like it /would/ have been useful to choose a physically larger
fuse and holder on this occasion.

On Tue, 15 Apr 2008 09:55:02 +0100 someone who may be Andy Burns
wrote this:-

The physical sizes of fuses are not useful.

Sounds like it /would/ have been useful to choose a physically larger
fuse and holder on this occasion.

Quite likely. However, only some ranges of fuses have different
physical sizes for different electrical "sizes".


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

"David Hansen" wrote in message
...
On Tue, 15 Apr 2008 08:55:31 +0100 someone who may be charles
wrote this:-

an ordinary 1.25" cartridge fuse

What's one of those?

CPC part number: FS01458 etc.

http://cpc.farnell.com says there is no such part.

To be of any use to people the OP should have given some useful
information, such as the current rating and (perhaps) the breaking
capacity of the fuse. The physical sizes of fuses are not useful.

If the intention was to be a little more coy then whether the
dimension quoted was the length or diameter would have been useful.


The physical size of the fuse IS important when you are considering
spark-gaps etc, which is what caused the dramatic failure in this case.

"1.25" cartridge fuse" is a well known specification, I use them daily.

On Tue, 15 Apr 2008 11:16:45 +0200 someone who may be "Clive"
wrote this:-

The physical size of the fuse IS important when you are considering
spark-gaps etc, which is what caused the dramatic failure in this case.

Incorrect. What is important in this respect is the breaking
capacity of the fuse. Different designs of fuse, with the same
physical dimensions, are able to reliably break different currents.
The same is true of different designs of miniature circuit breaker.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

"David Hansen" wrote in message
...
On Tue, 15 Apr 2008 11:16:45 +0200 someone who may be "Clive"
wrote this:-

The physical size of the fuse IS important when you are considering
spark-gaps etc, which is what caused the dramatic failure in this case.

Incorrect. What is important in this respect is the breaking
capacity of the fuse. Different designs of fuse, with the same
physical dimensions, are able to reliably break different currents.
The same is true of different designs of miniature circuit breaker.


Depending on the voltage and not the current !

From the OP's description, the voltage was high enough so that when the fuse
blew, the air gap was insufficient to stop a spark forming, hence ionizing
the air in what had been the fuse housing causing the fuse holder to
disintegrate. In this case, it seems that the fuse was physically (and not
electrically) too small to stop this happening, regardless of the current.

//Clive.

On Tue, 15 Apr 2008 12:02:40 +0200 someone who may be "Clive"
wrote this:-

Depending on the voltage and not the current !

Any fuse holder will have a rated maximum voltage.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54