House of Horrors

In article ,
Graham wrote:
On the subject of plug fuses,
Most of the equipment I install is powered by an IEC
13A plug (kettle lead)
Sometimes during an installation they get mixed up
And in some cases I have to replace them with
cables that have an Electrak plug (also fused)
http://www.electrak.co.uk/products_accessories.php

I recently did a fuse inventory
Most of the kit like Dell computers and monitors and
various printers were supplied with 5A fused plugs
The Brother laser printers came with 13A fuses.
Quick-heat fuser so not surprising.

The big surprise for me was the Cisco 1801 router
which sports an IEC lead with a 10A fuse.

The plug fuse is only required to protect the actual mains lead, so its
value is determined by that cable rating - and has nothing whatsoever to
do with the appliance which must have its own protection. Usually a
thermal fuse in the transformer windings these days.

--
*It ain't the size, it's... er... no, it IS ..the size.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
says...

I have standing orders from one of the local authorities I work for to
automatically replace any active device I find that is more than 20 years
old.

Does that include the management working there?
--

Dom Robinson Gamertag: DVDfever email: dom at dvdfever dot co dot uk
/* http://DVDfever.co.uk (editor)
/* 1132 DVDs, 347 games, 314 CDs, 110 cinema films, 42 concerts, videos & news
/* antibodies, steve hillage, burning crusade, sega psp, norah jones, kylie
New music charts - http://dvdfever.co.uk/music.shtml
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On 29 May, 20:54, "Bill Wright" wrote:
If I went into a loft and found a domestic distribution amplifier that was
dead I would test for a mains supply and if there was one I would scrap the
amp. I would bother checking whether someone had removed the fuse in the
plug top! The possibility of that is zero under normal circumstances, so it
would be reasonable to assume that either the plug top fuse had blown or the
amp had an internal fault. In either case the amp, which runs unattended in
the loft, has to be scrapped. It would be too risky to just change the fuse.
It would, in fact, be a seriously bad thing to do. So that part of the
programme was ********. Since they had the CAI on board I would have thought
they could have cooked up a better 'fault'. How about making it look as if
someone had put a heavy case in the loft and it had pulled the downlead out
of the amplifier's aerial socket? This is a common situation. Idiots!

You may have missed the recent post by one of the denizens of this
group suggesting that CAI may stand for Cowboys and Indians!

On Tue, 29 May 2007 22:02:28 +0100, Prometheus
wrote:

In article , Bill Wright
writes
If I went into a loft and found a domestic distribution amplifier that was
dead I would test for a mains supply and if there was one I would scrap the
amp. I would bother checking whether someone had removed the fuse in the
plug top! The possibility of that is zero under normal circumstances, so it
would be reasonable to assume that either the plug top fuse had blown or the
amp had an internal fault. In either case the amp, which runs unattended in
the loft, has to be scrapped. It would be too risky to just change the fuse.
It would, in fact, be a seriously bad thing to do.

Fuses do fail with age; I have had a few which have failed after many
years operation, when I check the current consumption I find it to be as
expected, so I replace the failed fuse and the kit continues to work.

Indeed, in fact we had a routine on a piece of equipment in work that
required all the fuses to be replaced every 5000 or 10000 hours (ISTR)
- fuses from 0.5A up to 200A - I don't ever remember doing it though
--
Cheers

Peter

Please remove the invalid to reply

On Wed, 30 May 2007 20:48:35 +0100, "Graham" wrote:


Mike I am typing this slowly in case I get too technical for you.

You concede that either the plug-top fuse had blown or the amp
had an internal fault.

I assume that in this situation we are not going to attempt a
repair on the latter.

What's the likely current drawn from the mains by a typical domestic
aerial amp? Lets say for the sake of argument 100mA, in practice
it will be well under that figure.

What is the lowest value plug top fuse that is readily obtainable?
Answer 3000mA that's well over half a kilowatt. If available
continuously that's more than enough to start a fire.

Trust me, a 3A fuse will not blow with only a 100mA load, particularly
in this situation where it is on continuously.

Do we still want to try another fuse? FFS, remember where we are,
Do we want to risk tripping an RCD or MCB?


I used to see a lot of this stuff. What happens is the primary
winding of the miniature power transformer gets shorted turns
and gets very hot. Even in this condition the amplifier can
continue to work, until the fuse blows. I would expect the
internal protection to kick in first of course, the plug
fuse blowing suggests catastrophic failure.

It's worth noting that the vast majority of electrical items in the
home (but not mine) have plug tops that are equipped with 13A fuses -
coz it says on the plug 13A !!
--
Cheers

Peter

Please remove the invalid to reply

"Bill Wright" wrote in message
...

"Norbert Wittgenfeld" wrote in message
...
So loft amplifiers are a serious fire hazard then?

No, of course they aren't, any more than any other device that draws power
from the mains. But some of them (those in plastic cases) can start a
fire. I've seen it once in 40 years. I've seen quite a few where the amp
has melted into a blob but hasn't caused a fire.


I always wondered about the wisdom of attaching these units directly to
wooden rafters so I mounted mine on a metal plate. It has been turned on for
the past 20+ years. I used to turn it off when I went on holiday, but now I
often forget.

My network router is also in my attic but it is not on a metal plate, and
unlike the tv amp, has a separate power supply.

--
Michael Chare

In message , Peter Thomas
writes
On Tue, 29 May 2007 22:02:28 +0100, Prometheus
wrote:

In article , Bill Wright
writes
If I went into a loft and found a domestic distribution amplifier that was
dead I would test for a mains supply and if there was one I would scrap the
amp. I would bother checking whether someone had removed the fuse in the
plug top! The possibility of that is zero under normal circumstances, so it
would be reasonable to assume that either the plug top fuse had blown or the
amp had an internal fault. In either case the amp, which runs unattended in
the loft, has to be scrapped. It would be too risky to just change the fuse.
It would, in fact, be a seriously bad thing to do.

Fuses do fail with age; I have had a few which have failed after many
years operation, when I check the current consumption I find it to be as
expected, so I replace the failed fuse and the kit continues to work.

Indeed, in fact we had a routine on a piece of equipment in work that
required all the fuses to be replaced every 5000 or 10000 hours (ISTR)
- fuses from 0.5A up to 200A - I don't ever remember doing it though

I wonder how many pieces of equipment would then fail when re-powered?
Ian.
--

"Peter Thomas" wrote in
message

I used to see a lot of this stuff. What happens is the primary
winding of the miniature power transformer gets shorted turns
and gets very hot. Even in this condition the amplifier can
continue to work, until the fuse blows. I would expect the
internal protection to kick in first of course, the plug
fuse blowing suggests catastrophic failure.

It's worth noting that the vast majority of electrical items in the
home (but not mine) have plug tops that are equipped with 13A fuses -
coz it says on the plug 13A !!

Well a 13A fuse will blow in the event of a dead short in the lead or the
primary of the mains transformer, and a 3A one *won't* blow in the event of
a more subtle fault such as a short in the output from the mains
transformer - so I reckon 13A for everything provides as much practical
protection as a 3A, even for low consumption appliances.

--
Max Demian

Max Demian wrote:

Well a 13A fuse will blow in the event of a dead short in the lead or the
primary of the mains transformer, and a 3A one *won't* blow in the event of
a more subtle fault such as a short in the output from the mains
transformer - so I reckon 13A for everything provides as much practical
protection as a 3A, even for low consumption appliances.

You are confusing fault with overcurrent protection. Fuses protecting a
lead may need to offer both. A short 3A flex will usually be adequately
protected from fault currents (i.e. short circuits, giving rise to
massive current flow) by a 13A fuse. However a sustained overload of 10A
say, would result in destruction of the flex.

A short on the primary of the transformer (depending on location) could
result in a long term high loading that conceivably a 3A fuse would
clear, and a 13A would not.

--
Cheers,

John.

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On May 31, 12:32 pm, John Rumm wrote:

You are confusing fault with overcurrent protection. Fuses protecting a
lead may need to offer both. A short 3A flex will usually be adequately
protected from fault currents (i.e. short circuits, giving rise to
massive current flow) by a 13A fuse. However a sustained overload of 10A
say, would result in destruction of the flex.

A short on the primary of the transformer (depending on location) could
result in a long term high loading that conceivably a 3A fuse would
clear, and a 13A would not.

I didn't see the programme. Out of interest where was the plug for the
amp plugged in. Surely not into a 13 A socket fed from the nearest
ceiling rose ? ;-)