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Default Are 3A plug fuses really necessary? Why not always 13A?

Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.
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Default Are 3A plug fuses really necessary? Why not always 13A?

David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


It depends on the cross sectional area of the cable cores. As is
correctly pointed out in the thread, the fuse is to protect against
cable faults, not internal faults in the box. If the cores are too
small, a 13 A fuse may not blow or carry enough current to rapidly trip
the MCB, leading to a cable that at the best is going to melt the
insulation, and at worst may start a fire.


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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 18:50, John Williamson wrote:

It depends on the cross sectional area of the cable cores. As is
correctly pointed out in the thread, the fuse is to protect against
cable faults, not internal faults in the box. If the cores are too
small, a 13 A fuse may not blow or carry enough current to rapidly trip
the MCB, leading to a cable that at the best is going to melt the
insulation, and at worst may start a fire.



Just anecdotally, I had a decorator in my house using a steam stripper.
He asked to borrow an extension lead, and I conscientiously checked the
extension lead was man enough for the job, then left him to it. Half an
hour later, the power went off.

Investigating, I found that he hadn't bothered to unreel more of the
extension cable than he needed to reach the job - despite clear
instructions on the reel to that effect. The entire lot inside the reel
had melted, and the power went off when the cores touched. This was a
man who had been doing this sort of work for over 10 years, mind.


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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 20:19, GB wrote:
On 07/11/2012 18:50, John Williamson wrote:

It depends on the cross sectional area of the cable cores. As is
correctly pointed out in the thread, the fuse is to protect against
cable faults, not internal faults in the box. If the cores are too
small, a 13 A fuse may not blow or carry enough current to rapidly trip
the MCB, leading to a cable that at the best is going to melt the
insulation, and at worst may start a fire.



Just anecdotally, I had a decorator in my house using a steam stripper.
He asked to borrow an extension lead, and I conscientiously checked the
extension lead was man enough for the job, then left him to it. Half an
hour later, the power went off.

Investigating, I found that he hadn't bothered to unreel more of the
extension cable than he needed to reach the job - despite clear
instructions on the reel to that effect. The entire lot inside the reel
had melted, and the power went off when the cores touched. This was a
man who had been doing this sort of work for over 10 years, mind.


Have to admit I have done the same. Stripper well within reels
capability but it cut out after a while. My reel has an overheat cut-out
fortunately. Lesson learned for all types of wiring.

If I take anything bought in Spain back to the UK I will have to change
the plug or use it through a correctly fused adaptor. Using them unfused
on a 30A ring main could be a recipe for disaster.

Worries me sightly that lamps and other itmes out here with thin flex
plug into fairly highly rated power sockets.
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:

Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.



Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.

[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?

The appliance manufactures seem to think so.

Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables

A Dell PC with a 5A fuse in the plug
A Cisco router with a 10A fuse
A Brother laser printer with 13A fuse.

Of course this might now create issues with interchangability.
I would be interested to see your comments about the above.


--
Graham.
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote:

Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197
Is there a counter-argument?
Thanks,
David.


All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires.

Old appliances are another matter, and many are not properly protected by a 13A fuse.

So its better to keep using 3A where suitable.


NT
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Default Are 3A plug fuses really necessary? Why not always 13A?

John Williamson wrote:
David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


It depends on the cross sectional area of the cable cores. As is
correctly pointed out in the thread, the fuse is to protect against
cable faults, not internal faults in the box. If the cores are too
small, a 13 A fuse may not blow or carry enough current to rapidly
trip the MCB, leading to a cable that at the best is going to melt the
insulation, and at worst may start a fire.


I am sure that some boiler installation manuals state the use of a 3A fuse -
and there is no legal reason why a boiler cannot be powered using a plug and
unswitched socket......

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Default Are 3A plug fuses really necessary? Why not always 13A?

David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.

13A fuses can go with a right bang, frightening old ladies. 3A fuses are
nicer.

Bill
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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 20:33, wrote:
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote:

Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a
counter-argument? Thanks, David.


All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.

Old appliances are another matter, and many are not properly
protected by a 13A fuse.

So its better to keep using 3A where suitable.


NT

Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.

--
Rod
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote:

All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.


Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.


That would be interesting.

The big bad assumption made in the digital spy thread was to assume only
short circuit faults and that massive currents will flow. In that
particular case there is little difference between a 3A or 13A fuse.

However if the short circuit current is only high, maybe limited by weak
spring tension in the fuse holder, corosion of the holdler/fuse cap,
dodgy wire termination some where, and say only 20A is flowing. Thene
there is a significant difference between a 3A and 13A fuse.

--
Cheers
Dave.





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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 07 Nov 2012 19:19:33 +0000, GB wrote:

Investigating, I found that he hadn't bothered to unreel more of the
extension cable than he needed to reach the job - despite clear
instructions on the reel to that effect. The entire lot inside the reel
had melted, and the power went off when the cores touched. This was a
man who had been doing this sort of work for over 10 years, mind.


And was his comment "That's odd. The last time I used a cable reel like
that one, the same thing happened".

I hope he paid for a replacement.

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Dave.



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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/12 21:40, Dave Liquorice wrote:
On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote:

All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.


Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.


That would be interesting.

The big bad assumption made in the digital spy thread was to assume only
short circuit faults and that massive currents will flow. In that
particular case there is little difference between a 3A or 13A fuse.

However if the short circuit current is only high, maybe limited by weak
spring tension in the fuse holder, corosion of the holdler/fuse cap,
dodgy wire termination some where, and say only 20A is flowing. Thene
there is a significant difference between a 3A and 13A fuse.

Or more to the point, under overcurrent, which would you rather have go?
a thin piece of flex with plastic insulation lying over a newspaper, or
a fuse in a plug.


--
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(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?



Counter to what?

Frank1 is obviously missing a clue.

grahamthompson and Nigel Goodwin seem to have explained more than
adequately.

Its easy enough to check. From the BS7671:2008 table 41.3[1], the
maximum earth loop impedance for a circuit protected by a B32 MCB is
1.44 ohms. That is what gives a fault current on the longest path of the
circuit of around 160A - or enough to open a B32 MCB on the "instant"
part of its trip response.

So we could take that as an example of the minimum fault current the
flex will need to withstand when someone shorts it.

Lets say the appliance has a flex with 0.5mm^2 CSA conductors. For a
short flex (i.e. typically 1.8m) you can ignore the additional
resistance of the flex, so can just assume the prospective fault current
of 160A. Now that should open a 13A fuse in less than 0.1 secs (probably
significantly less). So all you need to know is, will the flex will
carry that fault current for long enough to allow the fuse to do its
stuff without either vaporising or bursting into flames.

So we can work out the minimum size (s) of conductor required for that
with the adiabatic equation[2] and the PVC cable type k value of 115.

s = sqrt( 160^2 x 0.1 ) / 115

s = 0.44mm^2

Which is less that the actual flex CSA of 0.5mm^2, so in this particular
example the flex would actually be adequately protected by the 32A MCB
at the origin of the circuit (although the fuse will probably open
before the MCB gets a chance to operate)

If you try that sum on a shorter circuit - or one with a lower Ze, then
you may get an ELI of say 0.5 ohms at the end of the flex. That gives a
fault current of 460A which would need a conductor size of aver 1mm^2 to
be protected by the main MCB, so here the fuse would be essential.

(if the circuit were protected by a BS3036 rewireable fuse, or the
circuit a tad out of spec, the flex longer or thinner etc then the fuse
in the plug would be essential).



[1]
http://wiki.diyfaq.org.uk/index.php?...Loop_Impedance

[2]
http://wiki.diyfaq.org.uk/index.php?...abatic _Check

--
Cheers,

John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:

Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.



Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.

[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.

However what you say is also true, and in no way conflicts with that.

More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.

The appliance manufactures seem to think so.

Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)

(IEC perhaps?)

A Dell PC with a 5A fuse in the plug
A Cisco router with a 10A fuse
A Brother laser printer with 13A fuse.

Of course this might now create issues with interchangability.
I would be interested to see your comments about the above.


For stuff running with "normal" IEC leads its does not make any real
difference. The appliance will have an internal fuse if it needs it, and
the cables are quite sturdy (assuming they are not Chinese knock offs!)
The kit will have been designed to run safely on 16A circuits with no
plug fuse (as it will need to in most countries) so the flex will be
specced to suit.

IME leads for IT kit doe get swapped about without any regard for their
rating (most people have not even spotted there are two different specs
of lead and fuse). So 3A fusing may be pushing your luck depending on
what it gets connected to.


--
Cheers,

John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 21:40, Dave Liquorice wrote:
On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote:

All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.


Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.


That would be interesting.

The big bad assumption made in the digital spy thread was to assume only
short circuit faults and that massive currents will flow. In that
particular case there is little difference between a 3A or 13A fuse.

However if the short circuit current is only high, maybe limited by weak
spring tension in the fuse holder, corosion of the holdler/fuse cap,
dodgy wire termination some where, and say only 20A is flowing. Thene
there is a significant difference between a 3A and 13A fuse.


If there is only 20A of fault current, then there is 11.5 ohms of
resistance somewhere! The 4kW you are dissipating in the fuse holder
might be more of a worry than whatever is going on with the flex ;-)

--
Cheers,

John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 20:41, Bill Wright wrote:
David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.

13A fuses can go with a right bang, frightening old ladies. 3A fuses are
nicer.


You want to see the bang with the counterfeit ones arriving with your
latest mains lead from China via ebay:

http://s833.beta.photobucket.com/use...tFuse.mp4.html

or

http://www.bs1363.org.uk/counterfeit_fuse.mpeg



--
Cheers,

John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 07 Nov 2012 22:34:50 +0000, John Rumm
wrote:

On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:

Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.



Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.

[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.

However what you say is also true, and in no way conflicts with that.

More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.

The appliance manufactures seem to think so.

Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)

(IEC perhaps?)


Damn. that will teach me to proof read my own regurgitated words. In
the original thread you quipped:
"You can see why SATA became popular if the IDE leads were that size"

--
Graham.
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote:
On 07/11/2012 20:33, wrote:
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote:



Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a
counter-argument? Thanks, David.


All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.

Old appliances are another matter, and many are not properly
protected by a 13A fuse.

So its better to keep using 3A where suitable.


Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.


Unfortuately no, I've not kept any notes of those points. One thing it has changed is the minimum permissible conductor cross section in appliance leads, if you look at appliances from the 50s and 60s, some shavers & clocks etc have very thin conductors. Now all new flexes need to be able to survive the i squared t of a 13A fuse blow.


NT
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland
wrote:

On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


In the early days of colour TV I was told by a TV engineer that the
correct plug fuse for a CTV was 7A to allow for the switch-on current
surge of the degaussing circuitry.

I don't know whether or not "intermediate" BS1362 fuses such as 5A or
7A are still available.

In fact, was there not also a 1A BS1362 fuse, used for clock plugs,
but not shaver adaptors (or was it the other way round?)?

--
Frank Erskine


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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 23:55, wrote:
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote:
On 07/11/2012 20:33,
wrote:
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson
wrote:



Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is
there a counter-argument? Thanks, David.


All modern appliances and leads are required to be safe with a
13A fuse. However the reality is that fires do happen, and there
are at least some faults where a 3A would blow before a 13A, so
maybe preventing a small percentage of fires.

Old appliances are another matter, and many are not properly
protected by a 13A fuse.

So its better to keep using 3A where suitable.


Please can you provide a reference to when that changed? And,
ideally, what the requirements actually are - in an accessible
form.


Unfortuately no, I've not kept any notes of those points. One thing
it has changed is the minimum permissible conductor cross section in
appliance leads, if you look at appliances from the 50s and 60s, some
shavers & clocks etc have very thin conductors. Now all new flexes
need to be able to survive the i squared t of a 13A fuse blow.


NT

Heigh-ho. Anyone else know?

--
Rod
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Default Are 3A plug fuses really necessary? Why not always 13A?

On Wed, 07 Nov 2012 22:44:35 +0000, John Rumm
wrote:

On 07/11/2012 20:41, Bill Wright wrote:
David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.

13A fuses can go with a right bang, frightening old ladies. 3A fuses are
nicer.


You want to see the bang with the counterfeit ones arriving with your
latest mains lead from China via ebay:

http://s833.beta.photobucket.com/use...tFuse.mp4.html

or

http://www.bs1363.org.uk/counterfeit_fuse.mpeg



I assure you there was no dummy fuse in the adapter I got with a
handheld transceiver from China recently.
http://www.flickr.com/photos/g3zvt/8...ream/lightbox/

The strange thing was that the charger supplied had a Euro plug, so
didn't fit this adapter anyway.

The black sleeving on the pins appears to be thin heatshrink that I
could easily pick odd with a fingernail.

I wonder what internal protection a wall-wart with a Euro or Stucco
pins has to have compared to one with our 13A pins?
Without an x-ray machine, you've only got their word that they are
safe, and they are not only at the mercy of a 32A MCB.

--
Graham.
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On Wed, 07 Nov 2012 23:56:09 +0000, Frank Erskine
wrote:

On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland
wrote:

On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


In the early days of colour TV I was told by a TV engineer that the
correct plug fuse for a CTV was 7A to allow for the switch-on current
surge of the degaussing circuitry.

I don't know whether or not "intermediate" BS1362 fuses such as 5A or
7A are still available.

In fact, was there not also a 1A BS1362 fuse, used for clock plugs,
but not shaver adaptors (or was it the other way round?)?


If I just reach in this drawer...
http://www.flickr.com/photos/g3zvt/8...ream/lightbox/

--
Graham.
%Profound_observation%
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Default Are 3A plug fuses really necessary? Why not always 13A?

polygonum wrote:
On 07/11/2012 23:55, wrote:
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote:
On 07/11/2012 20:33,
wrote:
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson
wrote:



Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is
there a counter-argument? Thanks, David.


All modern appliances and leads are required to be safe with a
13A fuse. However the reality is that fires do happen, and there
are at least some faults where a 3A would blow before a 13A, so
maybe preventing a small percentage of fires.

Old appliances are another matter, and many are not properly
protected by a 13A fuse.

So its better to keep using 3A where suitable.


Please can you provide a reference to when that changed? And,
ideally, what the requirements actually are - in an accessible
form.


Unfortuately no, I've not kept any notes of those points. One thing
it has changed is the minimum permissible conductor cross section in
appliance leads, if you look at appliances from the 50s and 60s, some
shavers & clocks etc have very thin conductors. Now all new flexes
need to be able to survive the i squared t of a 13A fuse blow.


NT

Heigh-ho. Anyone else know?


It was around the time the voltages were harmonised at 230V, flexes were
marked HAR and CE marking came in.
1995?


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Default Are 3A plug fuses really necessary? Why not always 13A?

On 07/11/2012 23:11, Graham. wrote:
On Wed, 07 Nov 2012 22:34:50 +0000, John Rumm
wrote:

On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:

Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?

Thanks,
David.


Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.

[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.

However what you say is also true, and in no way conflicts with that.

More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.

The appliance manufactures seem to think so.

Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)

(IEC perhaps?)


Damn. that will teach me to proof read my own regurgitated words. In
the original thread you quipped:
"You can see why SATA became popular if the IDE leads were that size"


Lol, which to be fair I had completely forgotten about until your
comment prompted me to search for it (well it was 18 months ago!)

Still nice to know that even of my memory is going I am still consistent
(or predictable!)


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John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

In article ,
Frank Erskine wrote:
On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland
wrote:


On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...

http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


In the early days of colour TV I was told by a TV engineer that the
correct plug fuse for a CTV was 7A to allow for the switch-on current
surge of the degaussing circuitry.


I don't know whether or not "intermediate" BS1362 fuses such as 5A or
7A are still available.


In fact, was there not also a 1A BS1362 fuse, used for clock plugs,
but not shaver adaptors (or was it the other way round?)?


clock plugs use a smaller fuse. They are 19mm long as opposed to 1" for
BS1362.

CPC stock 1A,2A,3A,5A,7A,10A & 13A in BS1362 size

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Default Are 3A plug fuses really necessary? Why not always 13A?

On Nov 7, 10:26*pm, Peter Crosland wrote:
On 07/11/2012 18:40, David Robinson wrote:

Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


That's about the size of it.

Years ago a "Euro-plug" was designed. It had no fuse and was a
throwback to the fifteen amp plugs we had nicely got rid of. I think
it was sixteen amp.
Fortunately it was abandoned. MK actually started making them.

I think the 13a plug is the only one in the world with a fuse.
There was another where the fuse was a screw-in pin on the plug.
Haven't seen one for years.
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Default Are 3A plug fuses really necessary? Why not always 13A?

Dave Liquorice wrote:

However if the short circuit current is only high, maybe limited by weak
spring tension in the fuse holder, corosion of the holdler/fuse cap,
dodgy wire termination some where, and say only 20A is flowing. Thene
there is a significant difference between a 3A and 13A fuse.


Exactly.
Like in the house I was working at this week. the best earth fault loop
reading I could get on the 30A fused socket outlets was 5.6 ohms.The
worst, 9ohms.
At the 'best' socket, with 5.6 ohms, at the measured voltage of 247V, it
would be passing 44 amps, which just wouldnt break the fusebox fuse.

At the worst socket, it would be passing 27 Amps, which may break a 13A
fuse, but I doubt it would do it in 0.4 of a second, more like a second,
which is enough to kill.
A 3A fuse would break it immediately (well, ok, in less than half a
second).
The fuse in the fusebox will be happlily buzzing away, passing the
current for half an hour before it broke. The figures were likely to be
worse in the evening, as other people came home, and the voltage may
drop a little, allowing more current through.

Ok, thats an extreme example, but a true one, so the final fuse rating
can have safety implications, hence best to put the lowest rating
possible in.

Alan.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On Nov 7, 10:35*pm, John Rumm wrote:
On 07/11/2012 20:20, Graham. wrote:









On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:


Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Thanks,
David.


Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.


[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.

However what you say is also true, and in no way conflicts with that.

More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.

The appliance manufactures seem to think so.


Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)

(IEC perhaps?)

A Dell PC with a 5A fuse in the plug
A Cisco router with a 10A fuse
A Brother laser printer with 13A fuse.


Of course this might now create issues with interchangability.
I would be interested to see your comments about the above.


For stuff running with "normal" IEC leads its does not make any real
difference. The appliance will have an internal fuse if it needs it, and
the cables are quite sturdy (assuming they are not Chinese knock offs!)
The kit will have been designed to run safely on 16A circuits with no
plug fuse (as it will need to in most countries) so the flex will be
specced to suit.

IME leads for IT kit doe get swapped about without any regard for their
rating (most people have not even spotted there are two different specs
of lead and fuse). So 3A fusing may be pushing your luck depending on
what it gets connected to.

--
Cheers,

John.

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Not all faults are dead shorts. Transformer overheat/burnout for
example.
Not all equipment has internal fuses.
3Kw/13a of sustained energy in an electronic device/small electric
motor could start a nice little fire.

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On Nov 7, 11:56*pm, Frank Erskine
wrote:
On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland
wrote:

On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is appropriate..


In the early days of colour TV I was told by a TV engineer that the
correct plug fuse for a CTV was 7A to allow for the switch-on current
surge of the degaussing circuitry.

I don't know whether or not "intermediate" BS1362 fuses such as 5A or
7A are still available.

In fact, was there not also a 1A BS1362 fuse, used for clock plugs,
but not shaver adaptors (or was it the other way round?)?

--
Frank Erskine


There was indeed. One was physically smaller than the plug fuse. You
found them in mains electric clock connectors. Of course, you never
see mains clocks any more except as radios.
There have been all sorts of odd sizes over the years.


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Default Are 3A plug fuses really necessary? Why not always 13A?

:
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote:
On 07/11/2012 20:33,
wrote:
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote:



Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a
counter-argument? Thanks, David.


All modern appliances and leads are required to be safe with a 13A
fuse. However the reality is that fires do happen, and there are at
least some faults where a 3A would blow before a 13A, so maybe
preventing a small percentage of fires.

Old appliances are another matter, and many are not properly
protected by a 13A fuse.

So its better to keep using 3A where suitable.


Please can you provide a reference to when that changed? And, ideally,
what the requirements actually are - in an accessible form.


Unfortuately no, I've not kept any notes of those points. One thing it
has changed is the minimum permissible conductor cross section in
appliance leads, if you look at appliances from the 50s and 60s, some
shavers & clocks etc have very thin conductors. Now all new flexes need
to be able to survive the i squared t of a 13A fuse blow.


I remember those thin leads. My '60s soldering iron had a lead about
half the diameter of (today's!) CAT5 patch cables. My assumption up
until now has been that globalisation has resulted in all leads being
designed for the unfused plugs used in most of the world outside the UK.

--
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On Thursday, November 8, 2012 7:43:36 AM UTC, harry wrote:
On Nov 7, 10:26 pm, Peter Crosland wrote:


Only the terminally stupid would use a 13A fuse when a 3A is appropriate.


That's about the size of it.
Years ago a "Euro-plug" was designed. It had no fuse and was a
throwback to the fifteen amp plugs we had nicely got rid of. I think
it was sixteen amp.
Fortunately it was abandoned. MK actually started making them.
I think the 13a plug is the only one in the world with a fuse.
There was another where the fuse was a screw-in pin on the plug.
Haven't seen one for years.


Optional mains plug fuses were in use a century ago in the UK, but they were open wire links in plugs that were often wooden. They were banned in 1913 as a fire risk.


NT
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In article
,
harry wrote:
On Nov 7, 10:26 pm, Peter Crosland wrote:
On 07/11/2012 18:40, David Robinson wrote:

Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Only the terminally stupid would use a 13A fuse when a 3A is
appropriate.


That's about the size of it.


Years ago a "Euro-plug" was designed. It had no fuse and was a
throwback to the fifteen amp plugs we had nicely got rid of. I think
it was sixteen amp.
Fortunately it was abandoned. MK actually started making them.


do you mean the CEEform plug? MK Commando, etc. Very much in use.

I think the 13a plug is the only one in the world with a fuse.


some of our old 5A round pin plugs had fuses. Perhasp they still do in
India.

There was another where the fuse was a screw-in pin on the plug.
Haven't seen one for years.


those were made by D&S.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On 08/11/2012 07:52, harry wrote:
On Nov 7, 10:35 pm, John Rumm wrote:
On 07/11/2012 20:20, Graham. wrote:









On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:


Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Thanks,
David.


Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.


[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.

However what you say is also true, and in no way conflicts with that.

More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.

The appliance manufactures seem to think so.


Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)

(IEC perhaps?)

A Dell PC with a 5A fuse in the plug
A Cisco router with a 10A fuse
A Brother laser printer with 13A fuse.


Of course this might now create issues with interchangability.
I would be interested to see your comments about the above.


For stuff running with "normal" IEC leads its does not make any real
difference. The appliance will have an internal fuse if it needs it, and
the cables are quite sturdy (assuming they are not Chinese knock offs!)
The kit will have been designed to run safely on 16A circuits with no
plug fuse (as it will need to in most countries) so the flex will be
specced to suit.

IME leads for IT kit doe get swapped about without any regard for their
rating (most people have not even spotted there are two different specs
of lead and fuse). So 3A fusing may be pushing your luck depending on
what it gets connected to.



Not all faults are dead shorts. Transformer overheat/burnout for
example.


For the purposes of this discussion they are (its in the definition of
"fault current")

Transformers are unlikely to be able to present any sustained load above
their design maximum for long - the wire size on their primary winding
will typically be *significantly* thinner than that of the supply flex.

Not all equipment has internal fuses.


If it needs overload protection then it is required to have its own
protection. Remember in most markets, protection via a plug fuse is not
an option.

3Kw/13a of sustained energy in an electronic device/small electric
motor could start a nice little fire.


Which would be an overload and not a fault. If there is a plausible
overload scenario, then the device in question must include its own
protection.


--
Cheers,

John.

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Default Are 3A plug fuses really necessary? Why not always 13A?

On Nov 8, 7:52*am, harry wrote:
On Nov 7, 10:35*pm, John Rumm wrote:









On 07/11/2012 20:20, Graham. wrote:


On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:


Not my question, or belief, but found here...


http://forums.digitalspy.co.uk/showthread.php?t=1755197


Is there a counter-argument?


Thanks,
David.


Here's a counter argument I made a couple of years ago in response to
those that say it's only there to protect the cable.


[It] May not be mandated for appliance protection, but isn't it true
to say that choosing
a plug fuse value sensibly having regard for the maximum current
demand of
the appliance rather than than just the capability of the cable has
always been good practice?


Indeed - but its not a counter argument. The logic Humax (or whoever)
are applying is that the 13A fuse is adequate to protect the flex. That
is demonstrably true.


However what you say is also true, and in no way conflicts with that.


More closely matching the actual size required will mean that when
things do go pear shaped, the actual energy let through may be a little
lower. Less spark, less heating stress on the cables etc.


The appliance manufactures seem to think so.


Take the case of three items I regularly install, all with supplied
0.75mm2 IDE cables


Strange place to be using a disk interface cable ;-)


(IEC perhaps?)


A Dell PC with a 5A fuse in the plug
A Cisco router with a 10A fuse
A Brother laser printer with 13A fuse.


Of course this might now create issues with interchangability.
I would be interested to see your comments about the above.


For stuff running with "normal" IEC leads its does not make any real
difference. The appliance will have an internal fuse if it needs it, and
the cables are quite sturdy (assuming they are not Chinese knock offs!)
The kit will have been designed to run safely on 16A circuits with no
plug fuse (as it will need to in most countries) so the flex will be
specced to suit.


IME leads for IT kit doe get swapped about without any regard for their
rating (most people have not even spotted there are two different specs
of lead and fuse). So 3A fusing may be pushing your luck depending on
what it gets connected to.


--
Cheers,


John.


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|-----------------------------------------------------------------|
| * * * *John Rumm - john(at)internode(dot)co(dot)uk * * * * * * *|
\================================================= ================/


Not all faults are dead shorts.


Is it Panto time yet? Oh yes they are.

And all short circuits are faults.

Anything else is an overload.

MBQ




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On Wednesday, November 7, 2012 11:56:12 PM UTC, Frank Erskine wrote:

In the early days of colour TV I was told by a TV engineer that the
correct plug fuse for a CTV was 7A to allow for the switch-on current
surge of the degaussing circuitry.

I don't know whether or not "intermediate" BS1362 fuses such as 5A or
7A are still available.

In fact, was there not also a 1A BS1362 fuse, used for clock plugs,
but not shaver adaptors (or was it the other way round?)?

1,2,3,5,7,10 and 13A fuses are all still available. I remember seeing 1A fuses in clock plugs - though some clock plugs used fuses with a different mechanical size just to be awkward...
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On 08/11/12 10:49, Man at B&Q wrote:
all short circuits are faults.

Anything else is an overload.

What a peculiar version of the english language you speak...

Lets say we have an SMPS, and due to a fault in the main 400V reservoir
on the mains side, it starts leaking several amps ...

You are saying that's not a fault?






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On Thursday, November 8, 2012 10:46:10 AM UTC, John Rumm wrote:
On 08/11/2012 07:52, harry wrote:
On Nov 7, 10:35 pm, John Rumm wrote:
On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote:




Not all faults are dead shorts. Transformer overheat/burnout for
example.


For the purposes of this discussion they are (its in the definition of
"fault current")


Welcome to the strange world of Aurthur Brown. The wiring regs use 'fault current' to specifically mean a dead short, but obviously in the real world appliance faults occur that produce current (fault current by definition) that covers the full range from a smallish increase than only overheats a motor to a dead short. Introducing a narrow perspective definition that applies specifically to wiring and using it outside of where it makes good sense is not productive, and insisting it must mean that elsewhere is illogical. In the world of electronics (which many appliances are) fault current does not usually mean a dead short across the mains.


Transformers are unlikely to be able to present any sustained load above
their design maximum for long - the wire size on their primary winding
will typically be *significantly* thinner than that of the supply flex.


Not all equipment has internal fuses.


If it needs overload protection then it is required to have its own
protection.


In practice not all has, particularly old appliances

Remember in most markets, protection via a plug fuse is not
an option.


Old UK appliances were typically designed for only the UK market

3Kw/13a of sustained energy in an electronic device/small electric
motor could start a nice little fire.


Which would be an overload and not a fault. If there is a plausible
overload scenario, then the device in question must include its own
protection.


But in practice a fair few don't. There are still significant numbers of old electrical goods in use spanning the range from pre-95 to 1920s. And not all new goods meet the standards legally required of them.


NT
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On Nov 8, 12:33*pm, The Natural Philosopher
wrote:
On 08/11/12 10:49, Man at B&Q wrote:
all short circuits are faults.

Anything else is an overload.


What a peculiar version of the english language you speak...

Lets say we have an SMPS, and due to a fault in the main 400V reservoir
on the mains side, it starts leaking several amps ...

You are saying that's not a fault?



Well, it is faulty, but in the jargon, that is not a fault current.

MBQ
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On Wednesday, November 7, 2012 8:20:19 PM UTC, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson

wrote:



Not my question, or belief, but found here...




http://forums.digitalspy.co.uk/showthread.php?t=1755197






Is there a counter-argument?




Thanks,


David.






Here's a counter argument I made a couple of years ago in response to

those that say it's only there to protect the cable.



[It] May not be mandated for appliance protection, but isn't it true

to say that choosing

a plug fuse value sensibly having regard for the maximum current

demand of

the appliance rather than than just the capability of the cable has

always been good practice?



The appliance manufactures seem to think so.



Take the case of three items I regularly install, all with supplied

0.75mm2 IDE cables



A Dell PC with a 5A fuse in the plug


That seems OK as few computers would exceed 1kw
but if that lead was used as a kettle lead.....


A Cisco router with a 10A fuse


No idea perhaps they had a lot of 10Amp fuses spare I have, I think they are black, 13Amp brown and 3A red.


A Brother laser printer with 13A fuse.


In the days ofm teh first laser printers they took quite a heaft startup current, in fact you shouldn;t put laswer printers on sureg protection blaocks either. Not sur eif it's still true as I can't believe the modern USB laserpriners would need a high startup cutrrent....




Of course this might now create issues with interchangability.

I would be interested to see your comments about the above.


I broguht about 100 "Y" leads that have two IEC sockets on the end and they have 13amp fuses. There's a health and safety notice that says were not allowed to use them as you can't connect two pieces of equipment to one plug..







--

Graham.

%Profound_observation%


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