Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

I've been checking some fuses (when I got bored over Christmas!) and
many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

On 29/12/2019 13:01, Scott wrote:

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

In the event of an internal fault in an appliance containing electronics
then the chances are that one of the components will release its smoke
and permanently disable the appliance much faster than the 'correctly'
rated fuse would blow. So not much point in trying to protect anything
except the lead.

On Sun, 29 Dec 2019 13:01:47 +0000, Scott
wrote:

Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

I've been checking some fuses (when I got bored over Christmas!) and
many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

BS 1362 plug fuses already have a margin greater than 50% built in. A
13 amp fuse can take 20 amps for a long time before it fails.

See:

https://www.diynot.com/diy/threads/b...istics.430472/

On 29/12/2019 13:01, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

3A, and 13A were typically the most common. (and originally the only
other commonly available value was 5A).

There seems have been a growth in use of 10A however - probably down to
the flood of dubious "13A" accessories and extension leads landing here
from the middle kingdom.

(Multiway extension leads being one of the few cases where the fuse
might have to offer overload protection)

I've been checking some fuses (when I got bored over Christmas!) and

You know how to have fun!

many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

Most appliances are designed with leads that will still have adequate
protection from a 13A fuse, since the designer must assume that is what
the less well informed may well fit.

Note that in most cases the protection being discussed is "fault" (i.e.
short circuit) protection and not overload. In those cases, so long as
the fuse blows quickly enough, the actual rating is not really that
important. However not "false" blowing on inrush etc, is more important.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

Keeps the production line easier, and smaller inventory of parts etc.
However your basic point is correct, you *might* get a "better" result
with a more closely matched fuse. (where better is hard to assess -
perhaps a lower fire risk in some cases, or perhaps a better sense of
satisfaction of having done it "right)

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

Depends on the motor, inrush on some induction motors can be 9x nominal.

When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

In those days appliances may not have had adequate internal protection,
and so relied on the plug fuse. Also many of the flexes would not have
had adequate fault protection with a 13A fuse.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 29/12/2019 14:49, Caecilius wrote:

BS 1362 plug fuses already have a margin greater than 50% built in. A
13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

On Sun, 29 Dec 2019 14:52:22 +0000, John Rumm
wrote:

On 29/12/2019 13:01, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

3A, and 13A were typically the most common. (and originally the only
other commonly available value was 5A).

There seems have been a growth in use of 10A however - probably down to
the flood of dubious "13A" accessories and extension leads landing here
from the middle kingdom.

(Multiway extension leads being one of the few cases where the fuse
might have to offer overload protection)

I've been checking some fuses (when I got bored over Christmas!) and

You know how to have fun!

Not as bad as a former colleague who complained when the managing
agents replaced the manufacturer's software in the lift with generic
software, which was detrimental to the user experience of the lift :-)

Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can run
from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

or perhaps a better sense of satisfaction of having done it "right)


Good enough for me.

On 29/12/2019 14:52, John Rumm wrote:

I appreciate that motors have a surge at the start.Â* I believe a 50%
margin should be added generally (more for a motor).

Depends on the motor, inrush on some induction motors can be 9x nominal.

In general the better the motor efficiency the worse is the surge.

10x is easily achievable wioth 'good' motors.

cheap chinese motors used in e.g. car window winders are deliberately
pants to that they can be stalled without burning out wires or fuses.


--
€œThere are two ways to be fooled. One is to believe what isnt true; the
other is to refuse to believe what is true.€�

€”Soren Kierkegaard

On 29/12/2019 15:38:13, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can run
from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

Doesn't his fix make a mockery of safe-zones?

On 29/12/2019 16:17:04, The Natural Philosopher wrote:
On 29/12/2019 14:52, John Rumm wrote:

I appreciate that motors have a surge at the start.Â* I believe a 50%
margin should be added generally (more for a motor).

Depends on the motor, inrush on some induction motors can be 9x nominal.

In general the better the motor efficiency the worse is the surge.

10x is easily achievable wioth 'good' motors.

cheap chinese motors used in e.g. car window winders are deliberately
pants to that they can be stalled without burning out wires or fuses.

Car window winders are an especially bad example. They use load sensors
to ensure nothing is trapped, such as a child's arm, in the window.

What we did before regulations! Apart from a few children losing arms
and suffocated children of course.

On 29/12/2019 17:04, Fredxx wrote:
On 29/12/2019 15:38:13, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can run
from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

Doesn't his fix make a mockery of safe-zones?

yes.

--
Adam

On 29/12/2019 14:49, Caecilius wrote:
On Sun, 29 Dec 2019 13:01:47 +0000, Scott
wrote:

Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

I've been checking some fuses (when I got bored over Christmas!) and
many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

BS 1362 plug fuses already have a margin greater than 50% built in. A
13 amp fuse can take 20 amps for a long time before it fails.

See:

https://www.diynot.com/diy/threads/b...istics.430472/

Looks like they pinched our scan :-)

http://wiki.diyfaq.org.uk/index.php/...ins_Plug_Fuses



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 29/12/2019 15:00, Mike Clarke wrote:
On 29/12/2019 14:49, Caecilius wrote:

BS 1362 plug fuses already have a margin greater than 50% built in.Â* A
13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Like true for a cable rated at 3A as well...

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 29/12/2019 19:34:21, ARW wrote:
On 29/12/2019 17:04, Fredxx wrote:
On 29/12/2019 15:38:13, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can
run from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

Doesn't his fix make a mockery of safe-zones?

yes.

It would have been better to move his switch down to be horizontally in
line with the cable.

Happy to show my ignorance, while 50mm from a wall corner is a
safe-zone, I didn't think the same was true behind an architrave for a
door way.

On 29/12/2019 21:54, Fredxx wrote:
On 29/12/2019 19:34:21, ARW wrote:
On 29/12/2019 17:04, Fredxx wrote:
On 29/12/2019 15:38:13, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than
it would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can
run from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

Doesn't his fix make a mockery of safe-zones?

yes.

It would have been better to move his switch down to be horizontally in
line with the cable.

Happy to show my ignorance, while 50mm from a wall corner is a
safe-zone, I didn't think the same was true behind an architrave for a
door way.



I totally agree with you.

That was a bit of messing about with the camera looking for the "joist".

Nothing that a connector rod would not have found in seconds.

Although IMHO he did well fitting a dry liner box in that wall.

--
Adam

On 29/12/2019 14:52, John Rumm wrote:
On 29/12/2019 13:01, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

3A, and 13A were typically the most common. (and originally the only
other commonly available value was 5A).

There seems have been a growth in use of 10A however - probably down to
the flood of dubious "13A" accessories and extension leads landing here
from the middle kingdom.

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

SteveW

In article ,
Steve Walker wrote:
On 29/12/2019 14:52, John Rumm wrote:
On 29/12/2019 13:01, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

3A, and 13A were typically the most common. (and originally the only
other commonly available value was 5A).

There seems have been a growth in use of 10A however - probably down to
the flood of dubious "13A" accessories and extension leads landing here
from the middle kingdom.

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I'd be more concerned about the lead having an earth connection. One I
bought off ebay recently had none.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

Fredxx wrote:

On 29/12/2019 19:34:21, ARW wrote:
On 29/12/2019 17:04, Fredxx wrote:
On 29/12/2019 15:38:13, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can
run from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

Doesn't his fix make a mockery of safe-zones?

yes.

It would have been better to move his switch down to be horizontally in
line with the cable.

Happy to show my ignorance, while 50mm from a wall corner is a
safe-zone, I didn't think the same was true behind an architrave for a
door way.

I would have thought it was exactly where a nail might go, I agree.

--

Roger Hayter

Fredxx wrote:

while 50mm from a wall corner is a safe-zone, I didn't think the same
was true behind an architrave for a door way

Didn't he saw he didn't plaster over it? So if it was left visible, no
problem :-P

Andy Burns wrote:

Fredxx wrote:

while 50mm from a wall corner is a safe-zone, I didn't think the same
was true behind an architrave for a door way

Didn't he saw he didn't plaster over it? So if it was left visible, no
problem :-P

Especially if you use a transparent architrave.
--

Roger Hayter

On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker
wrote:

On 29/12/2019 14:52, John Rumm wrote:
On 29/12/2019 13:01, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

3A, and 13A were typically the most common. (and originally the only
other commonly available value was 5A).

There seems have been a growth in use of 10A however - probably down to
the flood of dubious "13A" accessories and extension leads landing here
from the middle kingdom.

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

On 30/12/2019 10:18:19, Andy Burns wrote:
Fredxx wrote:

while 50mm from a wall corner is a safe-zone, I didn't think the same
was true behind an architrave for a door way

Didn't he saw he didn't plaster over it? So if it was left visible, no
problem :-P

If I was the leccy I would leave as is with cable visible and tell the
landlord to sort out the safe zones properly; where if he was to cover
the cable it would no longer be compliant.

On Monday, 30 December 2019 10:57:44 UTC, Roger Hayter wrote:
Especially if you use a transparent architrave.

They're used in *very* secure buildings where any tampering with the wiring or concealment of devices must be visible.

Owain

On Sunday, 29 December 2019 13:01:52 UTC, Scott wrote:
Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

I've been checking some fuses (when I got bored over Christmas!) and
many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?


A few things have either changed or been more widely recognised since the 1940s.

Back then appliances were routinely not suitably fused & designed to safely deal with internal faults. The plug fuse was a safety device for the appliance as well as the lead. Now it's usually not, it only remains so for historic appliances.

Leads were often very thin, basically what we now call speaker wire. Using under 3A fuses is wise if such wire is used.

Now most people are not expected to have any clue what value of fuse an appliance can or should run on - and don't. In the 40s it was expected that people would have some idea on this.

The financial saving of having fewer choices is now widely recognised & appreciated. Stocking 3 & 13A is cheaper than stocking 1, 2, 3, 5, 7, 10, 13A.

Ultimately yes, it's always safer to use the fuse that best suits each appliance. For historic goods that matters far more. I don't have any real data on what difference that approach can make to fire & death stats.


NT

On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.


NT

On 30/12/2019 22:14, wrote:
On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.

Not unusual for a gaming PC's CPU to use 120W when working hard and a
pair of graphics card to take 300W between them. That doesn't leave a
lot out of 500W for the motherboard, RAM, hard-disks/SSDs, etc.

SteveW

On Tuesday, 31 December 2019 01:02:51 UTC, Steve Walker wrote:
On 30/12/2019 22:14, tabbypurr wrote:
On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.

Not unusual for a gaming PC's CPU to use 120W when working hard and a
pair of graphics card to take 300W between them. That doesn't leave a
lot out of 500W for the motherboard, RAM, hard-disks/SSDs, etc.

SteveW

Sure, such systems are in use. Even those don't run flat out all the time. And mains fuses can provide double rated current for a long time.


NT

On Tue, 31 Dec 2019 01:02:43 +0000, Steve Walker
wrote:

On 30/12/2019 22:14, wrote:
On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.

Not unusual for a gaming PC's CPU to use 120W when working hard and a
pair of graphics card to take 300W between them. That doesn't leave a
lot out of 500W for the motherboard, RAM, hard-disks/SSDs, etc.

So my initial 'guesstimate' of 7A might be okay then (allowing for
surges)?

On Tuesday, 31 December 2019 09:50:59 UTC, Scott wrote:
On Tue, 31 Dec 2019 01:02:43 +0000, Steve Walker
wrote:
On 30/12/2019 22:14, tabbypurr wrote:
On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.

Not unusual for a gaming PC's CPU to use 120W when working hard and a
pair of graphics card to take 300W between them. That doesn't leave a
lot out of 500W for the motherboard, RAM, hard-disks/SSDs, etc.

So my initial 'guesstimate' of 7A might be okay then (allowing for
surges)?

any mains fuse from 2A or 3A up is ok, PCs are all modern appliances. 7A is far above necessary of course. The inrush current duration is too short to worry such a fuse.

On Tue, 31 Dec 2019 05:42:22 -0800 (PST), wrote:

On Tuesday, 31 December 2019 09:50:59 UTC, Scott wrote:
On Tue, 31 Dec 2019 01:02:43 +0000, Steve Walker
wrote:
On 30/12/2019 22:14, tabbypurr wrote:
On Monday, 30 December 2019 11:01:02 UTC, Scott wrote:
On Sun, 29 Dec 2019 23:41:59 +0000, Steve Walker

IIRC the IEC plugs commonly used on computer, hi-fi, entertainment
systems, even (hot version) kettles these days, are only rated for 10A.
As they may be swapped between devices, it'd make sense to make them all
rated 10A and use a 10A fuse.

I noticed that with two computer cables both fused at 10A. I replaced
the printer with 5A (claimed rating 2.5A). I don't know what to use
for the PC itself because of the array of components involved.
Thinking about 7A :-)

PCs typically take an amp or less. Only high power systems eat more. While '500w' PSUs are moderately common, they're normally not 500w, and a computer that eats 500w is an unusual animal. Hype rules.

Not unusual for a gaming PC's CPU to use 120W when working hard and a
pair of graphics card to take 300W between them. That doesn't leave a
lot out of 500W for the motherboard, RAM, hard-disks/SSDs, etc.

So my initial 'guesstimate' of 7A might be okay then (allowing for
surges)?

any mains fuse from 2A or 3A up is ok, PCs are all modern appliances. 7A is far above necessary of course. The inrush current duration is too short to worry such a fuse.

Thanks.

On 29/12/2019 15:38, Andy Burns wrote:
Mike Clarke wrote:

Caecilius wrote:

A 13 amp fuse can take 20 amps for a long time before it fails.

I expect a cable rated for 13A would also survive for longer than it
would take for the 13A fuse to blow.

Apparently showers (Riba seem to be either 8.5, 9.5 or 10.5kW) can run
from a 13A FCU with some 1mm flex

https://youtu.be/AOZmgi8sdd8?t=121

It might run for a while but will get very hot!

In article ,
Scott wrote:
When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

Because to know what the correct size fuse is, you'd need to know the
cable size. Somewhat easier with removable plugs, but guesswork with
moulded types.

And perhaps most only want to get the thing working again, so will fit any
fuse they have to hand, or can buy easily. Most likely 13 amp.

--
*Keep honking...I'm reloading.

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

On Wed, 01 Jan 2020 12:37:20 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

Because to know what the correct size fuse is, you'd need to know the
cable size. Somewhat easier with removable plugs, but guesswork with
moulded types.

How is it 'guesswork'? The manufacturer must know when they select
the fuse.

And perhaps most only want to get the thing working again, so will fit any
fuse they have to hand, or can buy easily. Most likely 13 amp.

Okay, but any sensible person would replace like for like. You could
say the same about 3A fuses. By your logic all electrical appliances
should be fitted with a 13A cable just in case someone decides to fit
a 13A fuse at a later stage.

On Monday, 30 December 2019 22:12:42 UTC, wrote:
Leads were often very thin, basically what we now call speaker wire.
Using under 3A fuses is wise if such wire is used.

Leads were also longer as people had fewer sockets. Remember the days you'd get a good 2 or 3 yards of flex on a table lamp.

Now all EU appliances are supposed to be okay with unfused plugs as that's normal in Europe, and leads are shorter to provide less resistance so a higher rated fuse/MCB blows quickly enough.

Lucky Golden Hedgehog leads from China are still on the thin side though.

Owain

In article ,
Scott wrote:
On Wed, 01 Jan 2020 12:37:20 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

Because to know what the correct size fuse is, you'd need to know the
cable size. Somewhat easier with removable plugs, but guesswork with
moulded types.

How is it 'guesswork'? The manufacturer must know when they select
the fuse.

And you can be sure it hasn't been replaced?

And perhaps most only want to get the thing working again, so will fit any
fuse they have to hand, or can buy easily. Most likely 13 amp.

Okay, but any sensible person would replace like for like. You could
say the same about 3A fuses. By your logic all electrical appliances
should be fitted with a 13A cable just in case someone decides to fit
a 13A fuse at a later stage.

But many ain't sensible. Hence small cables not being used with fitted 13
amp plugs these days.

--
*No radio - Already stolen.

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

On Wed, 1 Jan 2020 05:21:54 -0800 (PST),
wrote:

On Monday, 30 December 2019 22:12:42 UTC, wrote:
Leads were often very thin, basically what we now call speaker wire.
Using under 3A fuses is wise if such wire is used.

Leads were also longer as people had fewer sockets. Remember the days you'd get a good 2 or 3 yards of flex on a table lamp.

Now all EU appliances are supposed to be okay with unfused plugs as that's normal in Europe, and leads are shorter to provide less resistance so a higher rated fuse/MCB blows quickly enough.

Lucky Golden Hedgehog leads from China are still on the thin side though.

If the purpose of the fuse is to protect the flex (as is often said),
does this mean all flexes can cope with 16 amps (European radial
circuit)?

On 01/01/2020 13:07, Scott wrote:

Okay, but any sensible person would replace like for like. You could
say the same about 3A fuses.

That works on the assumption that most people are sensible.

There are many who would happily keep trying the next larger size fuse
until it 'worked'.

On Wed, 01 Jan 2020 13:58:42 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
On Wed, 01 Jan 2020 12:37:20 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?

Because to know what the correct size fuse is, you'd need to know the
cable size. Somewhat easier with removable plugs, but guesswork with
moulded types.

How is it 'guesswork'? The manufacturer must know when they select
the fuse.

And you can be sure it hasn't been replaced?

And perhaps most only want to get the thing working again, so will fit any
fuse they have to hand, or can buy easily. Most likely 13 amp.

Okay, but any sensible person would replace like for like. You could
say the same about 3A fuses. By your logic all electrical appliances
should be fitted with a 13A cable just in case someone decides to fit
a 13A fuse at a later stage.

But many ain't sensible. Hence small cables not being used with fitted 13
amp plugs these days.

But according to your logic the fuse might be replaced so I think you
are contradicting yourself here.

You could still end up with a 3 amp cable and 13 amp fuse, unless you
are saying all cables are 13 amp.

I cannot see how the manufacturer fitting a higher rated fuse assists
safety in any way.

On Wed, 1 Jan 2020 14:39:45 +0000, Mike Clarke
wrote:

On 01/01/2020 13:07, Scott wrote:

Okay, but any sensible person would replace like for like. You could
say the same about 3A fuses.

That works on the assumption that most people are sensible.

There are many who would happily keep trying the next larger size fuse
until it 'worked'.

So all appliances are designed to be safe with a 13 amp fuse? The
flex on the lamp I bought from John Lewis does not look to me that it
could carry 13 amps but I could be wrong. I won't be trying it out.