Gentlemen,

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

Cursitor Doom wrote:

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

I think you need closer to 4A to get out of the "forever" zone

https://docs.rs-online.com/9819/0900766b8002b71e.pdf

On 16/08/2020 18:42, Andy Burns wrote:
Cursitor Doom wrote:

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

I think you need closer to 4A to get out of the "forever" zone

https://docs.rs-online.com/9819/0900766b8002b71e.pdf

That is true of the BS1362 fuse.

The OP has not said what type of fuses he has bought - the 6 minute
maximum might suggest a glass fuse of some kind?



--
Adam

On 16/08/2020 14:10, Cursitor Doom wrote:
Gentlemen,

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

It is going to depend so much on the fuse holder. Try it with 4A. Only a
sensitive fast blow fuse is likely to go pop with just a 50% overload.

Unless you are using it with wire that cannot carry 2A it is academic.

Our church tea ladies managed to get two 3kW kettles powered from a 4
way extender off a single 13A socket pretty regularly without ever
blowing any fuses. They did once melt the extension cable though.

All the VH ones have thermal cutouts now to defend against such abuse.

--
Regards,
Martin Brown

On 16/08/2020 14:10, Cursitor Doom wrote:
Gentlemen,

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service.

what kind of fuse?

So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png





--
Cheers,

John.

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

When did it blow then?
Brian

--
--
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Cursitor Doom" wrote in message
...
Gentlemen,

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

In the main, small current fuses often are allowed to take a surge at start
up as well, at least the ones in plugs are. As long as they do not overheat
and melt the plastic but blow if the device current suddenly increases in a
major wee then I'm happy, otherwise you would be forever changing them, I'd
imagine.
Brian

--
--
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Andy Burns" wrote in message
...
Cursitor Doom wrote:

I acquired a batch of 2 Amp fuses recently from an unverified source
and decided it might be wise to test them before pressing them into
service. So I hooked one at random up to a power supply and pumped 3A
through it, waiting for it to blow. Now IIRC, it's supposed to blow
before 6 minutes maximum, yet this one kept right on going. I know
there's a general misunderstanding about how fuses work and people
expect them to blow instantly on any amount of over-current, but
that's not how it works in practice. But 6 minutes of 3A?
What does the Panel think?

I think you need closer to 4A to get out of the "forever" zone

https://docs.rs-online.com/9819/0900766b8002b71e.pdf

On Mon, 17 Aug 2020 07:41:30 +0100, "Brian Gaff \(Sofa\)"
wrote:

When did it blow then?


It didn't, Brain. I got bored after 20 minutes and turned it off.

On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.


--
Cheers,

John.

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

On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all. I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

On Monday, 17 August 2020 16:59:34 UTC+1, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all. I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

2A fuses are certainly a little safer on low current loads, but they do not limit fault current, they merely trip faster at a given current & are thus less likely to permit a fire to start. They also have more chance of tripping before fire on an overheat overcurrent condition.


NT

On Mon, 17 Aug 2020 09:05:13 -0700 (PDT), wrote:

On Monday, 17 August 2020 16:59:34 UTC+1, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all. I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

2A fuses are certainly a little safer on low current loads, but they do not limit fault current, they merely trip faster at a given current & are thus less likely to permit a fire to start. They also have more chance of tripping before fire on an overheat overcurrent condition.

Thanks. I'm glad I am not going mad!

On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

Probably fake - the end caps look too shiny to be Bussman

Whoa! Not so fast, John. I said the picture was of the exact same
*type* NOT the actual fuses I have!

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

The ones I have actually *look* like really nice quality. They have
quite thick, substantial ceramic cases to contain any flames or hot
gases. I cracked a couple open to see inside.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

Not quite in this application. I'm resurrecting an old variac that
needs to be brought into the 21st century. It has no fuse on the
secondary side apart from a few other shortcomings safety-wise that
I'm in the process of eliminating. Damn useful things to have in
certain parts of the world, variacs.

Cursitor Doom wrote:

The ones I have actually *look* like really nice quality. They have
quite thick, substantial ceramic cases to contain any flames or hot
gases. I cracked a couple open to see inside.

was there sand?

On Mon, 17 Aug 2020 09:05:13 -0700 (PDT), wrote:

On Monday, 17 August 2020 16:59:34 UTC+1, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all. I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

2A fuses are certainly a little safer on low current loads, but they do not limit fault current, they merely trip faster at a given current & are thus less likely to permit a fire to start. They also have more chance of tripping before fire on an overheat overcurrent condition.


What's not to like about that? When a 13A fuse blows, it can release a
*lot* of energy and cause flame damage to surrounding surfaces. Not to
mention quite an alarming bang!

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

--
Cheers,

John.

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

On 17/08/2020 19:11, Cursitor Doom wrote:
On Mon, 17 Aug 2020 09:05:13 -0700 (PDT), wrote:

On Monday, 17 August 2020 16:59:34 UTC+1, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all. I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

2A fuses are certainly a little safer on low current loads, but they do not limit fault current, they merely trip faster at a given current & are thus less likely to permit a fire to start. They also have more chance of tripping before fire on an overheat overcurrent condition.


What's not to like about that? When a 13A fuse blows, it can release a
*lot* of energy and cause flame damage to surrounding surfaces.
Not to mention quite an alarming bang!

Not with a BS1362 compliant fuse - they should quench any arc and keep
it contained in the fuse.






--
Cheers,

John.

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

On 17/08/2020 19:08, Cursitor Doom wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

Probably fake - the end caps look too shiny to be Bussman

Whoa! Not so fast, John. I said the picture was of the exact same
*type* NOT the actual fuses I have!

So if yours are of the "exact same type", how are they not exactly the
same? :-)


Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

The ones I have actually *look* like really nice quality. They have
quite thick, substantial ceramic cases to contain any flames or hot
gases. I cracked a couple open to see inside.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

Not quite in this application. I'm resurrecting an old variac that
needs to be brought into the 21st century. It has no fuse on the
secondary side apart from a few other shortcomings safety-wise that
I'm in the process of eliminating. Damn useful things to have in
certain parts of the world, variacs.

Indeed, why I made the exception for historic kit where they designer
may have placed the onus on the person fitting the plug to provide
overload protection as well as fault protection.

(with time it became clear that joe public was not equipped to make
sensible choices in this area, and the modern practice of ensuring that
if overload protection was required, then it must be in the appliance
itself and not on the end of the flex where it can be changed at the
whim of anyone with access to a fuse (or bit of tin foil).



--
Cheers,

John.

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

On Monday, 17 August 2020 21:57:17 UTC+1, John Rumm wrote:
On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

When the BS1362 plug system was introduced in '47 the plug fuse was normally the appliance overload fuse, appliances mostly had little or more often no other overload failure protection. That has changed of course, but there are still millions of appliances that have no built-in overload protection and could benefit from it safety-wise.


NT

On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

Whatever you call it, if there is only 2 amps of it instead of 13 amps
nothing will convince me that is not safer.

On Mon, 17 Aug 2020 19:11:34 +0100, Andy Burns
wrote:

Cursitor Doom wrote:

The ones I have actually *look* like really nice quality. They have
quite thick, substantial ceramic cases to contain any flames or hot
gases. I cracked a couple open to see inside.

was there sand?

Nope. And AFAIC in this type of fuse of that rating, there normally
isn't any in any case.

On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.


You frequently use the term "fault current" which crops up frequently
when professional electrical engineers are discussing installations.
However, for everyone else, it requires clarification. I'm not an
electrician, so I have no idea when you use that term whether you're
referring to *short circuit* current or *earth leakage* current or
something else altogether (unless you use an example as you did above
but even that's not watertight). And then there's that lot that read
this through Homeownershub - God only knows what *they* make of it.
;-

[...]
(with time it became clear that joe public was not equipped to make
sensible choices in this area, and the modern practice of ensuring that
if overload protection was required, then it must be in the appliance
itself and not on the end of the flex where it can be changed at the
whim of anyone with access to a fuse (or bit of tin foil).

We used to use strips of milk bottle tops back in the day. But I'm
giving my age away now. ;-)

Cursitor Doom wrote:

Andy Burns wrote:

was there sand?

Nope. And AFAIC in this type of fuse of that rating, there normally
isn't any in any case.

The BS refers to "granular filling"

On Monday, 17 August 2020 22:29:49 UTC+1, Cursitor Doom wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:
On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:
On 17/08/2020 14:04, Cursitor Doom wrote:

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.


You frequently use the term "fault current" which crops up frequently
when professional electrical engineers are discussing installations.
However, for everyone else, it requires clarification. I'm not an
electrician, so I have no idea when you use that term whether you're
referring to *short circuit* current or *earth leakage* current or
something else altogether (unless you use an example as you did above
but even that's not watertight). And then there's that lot that read
this through Homeownershub - God only knows what *they* make of it.
;-

The electrical wiring regs' meaning of 'fault' is a hard zero ohm L-N short.. John uses that meaning. Those of us that are more into repairing things tend to use 'fault' to mean any failure to operate correctly. The I with some Es seems to like to define existing terms differently to everyone else, classic communication poor practice.


NT

On 17/08/2020 22:09, wrote:
On Monday, 17 August 2020 21:57:17 UTC+1, John Rumm wrote:
On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the
left of the 3A fuse curve would suggest that it might take
3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg



Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an
appropriate level of overload. Actually having the capacity to
interrupt the flow of current, and not exploding in your face
being some important ones!)

Seems there's even more leaway than I'd expected for
extended over-current tolerance. Perhaps we should never fit
anything bigger than a 10A fuse in a 13A plug? I think I'll
toss out all my 13A fuses to be on the safe side.

You could flip the argument, and say never fit anything other
than a 13A fuse. The purpose of the fuse (for any moderately
recent appliance anyway) is to provide *fault* protection to
the flex - and a 13A fuse will do that just fine.

The exceptions to this are some low quality multiway extension
leads where 10A would be more appropriate, or for historic
appliances and flexs, or cases where a manufacturer explicitly
cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted them to various low
current appliances, without any difficulties. How anyone can
argue that limiting the fault current is anything other than a
safety enhancement confounds me.

Because you are confusing fault current with overload current.
Fuses (or any other circuit protection device have *no* ability to
limit fault currents. The only thing that limits a fault current
the round trip impedance of the circuit with the fault. So if that
is 0.23 ohms, then your fault current is 1,000 A regardless of the
fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal
current rating is not important.

What matters is that the fuse has the breaking capacity to clear
the fault before something else (like the appliance flex) is
destroyed / catches fire.

This is a *totally different* discussion from overload protection -
foe example fitting a 13A fuse to a spur feeding multiple sockets
on a ring circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10
and 13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They
will all handle fault currents.

When the BS1362 plug system was introduced in '47 the plug fuse was
normally the appliance overload fuse, appliances mostly had little or
more often no other overload failure protection.

Agreed - hence why I mentioned it.

However a good deal of appliances (even then) don't actually need any
overload protection... So there is a danger that you could cause more
problems in the quest for "safety". (i.e. nuisance fuse blows, plugs
running warmer etc).

That has changed of
course, but there are still millions of appliances that have no
built-in overload protection and could benefit from it safety-wise.

I don't have a source of figures for how many are still out there. Do
you? Some, sure; millions perhaps?



--
Cheers,

John.

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

On 17/08/2020 22:09, Scott wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

Whatever you call it, if there is only 2 amps of it instead of 13 amps
nothing will convince me that is not safer.

Define safer?

So if your life support system were to fail with a blown fuse when there
is a mains spike because some well meaning but uninformed person
replaced the manufacture fitted 13A fuse with a 2A one "because its
safer", that would be better?

Think it though logically, what are you trying to achieve? Say you have
a table lamp that takes a single B22 fitting lamp. What is the highest
power lamp that it will take in that format? 250W or about an amp? Is
there any way a lamp could draw say 2kW for a sustained period to put
its flex at risk of dangerous overheating? The answer is not really (at
least not without determined and conscious action by the user to be a
complete numpty).

Now you say, ah but, its a lamp, 3A fuse is better... in a sense you are
right, there is no downsize other than needing to replace the one fitted
by the manufacturer. But what have you actually achieved? The thing that
does matter (i.e. power gets swiftly disconnected when you stick your
chair leg down on the flex and cause a short circuit), will happen
regardless of fuse rating, since you have say 100A of fault current to
play with[1].

Now there are some appliances that do have overload failure modes. If
they are old enough, they may not include their own protection, for
those, yes its important they are fitted with the "right" fuse. For
others it matters less than many worry about.

[1] 100A should be a fusing time well under 0.1 secs on a 13A fuse. So
for a PVC flex we can work out the conductor size required to cope with
the I^2 . t let through energy with the adiabatic equation:

s = sqrt( 100 ^ 2 x 0.1 ) / 115 = 0.27mm minimum CSA

(115 being the k factor for PVC insulated cable)

So even the smallest typical 0.5mm^2 CSA flex would be fine with any fuse.





--
Cheers,

John.

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

On 17/08/2020 22:29, Cursitor Doom wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg

Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.


You frequently use the term "fault current" which crops up frequently
when professional electrical engineers are discussing installations.

Indeed I do - and perhaps I assume (maybe too readily) that since its
discussed so often here, most readers will be aware of the term and how
understanding it is fundamental to the concepts of circuit protection.

However, for everyone else, it requires clarification. I'm not an
electrician, so I have no idea when you use that term whether you're
referring to *short circuit* current or *earth leakage* current or
something else altogether (unless you use an example as you did above
but even that's not watertight).

Here is a fairly succinct explanation:

http://wiki.diyfaq.org.uk/index.php/...oad_curre nts


(using the terms in the context of circuit rather than appliance
protection, but the same principles apply generally even if overloads
within a single appliance are harder to create)

And then there's that lot that read
this through Homeownershub - God only knows what *they* make of it.
;-

A faucet probably:-)


--
Cheers,

John.

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

On 17/08/2020 22:50, Andy Burns wrote:
Cursitor Doom wrote:

Andy Burns wrote:

was there sand?

Nope. And AFAIC in this type of fuse of that rating, there normally
isn't any in any case.

The BS refers to "granular filling"

It does, although its a kind of implied requirement. In section 8.1 on
general requirements for testing, it says

"If acceptance tests are required, they shall be selected from the type
tests as agreed between the manufacturer and the purchaser. Fuse links
supplied by the manufacturer shall be regarded as complying with the
requirements of this standard, provided that in the following respects
they are identical with those tested in the type tests:

1) the cartridge bodies have the same dimensions, material and method of
manufacture,

2) the caps or other end closures of the cartridge have the same
dimensions, materials and method of attachment and sealing,

3) the granular filler of the cartridge is of the same material, grain
size and completeness of filling,

4) the fuse elements and their arrangement are the same in every respect."


--
Cheers,

John.

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

On 17/08/2020 22:47, Cursitor Doom wrote:
[...]
(with time it became clear that joe public was not equipped to make
sensible choices in this area, and the modern practice of ensuring that
if overload protection was required, then it must be in the appliance
itself and not on the end of the flex where it can be changed at the
whim of anyone with access to a fuse (or bit of tin foil).

We used to use strips of milk bottle tops back in the day. But I'm
giving my age away now. ;-)

I find people are surprised we still have milk bottles (as deposited on
the doorstep at 5am by Kevin our milkman!)


--
Cheers,

John.

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

On 17/08/2020 23:04, wrote:
On Monday, 17 August 2020 22:29:49 UTC+1, Cursitor Doom wrote:

You frequently use the term "fault current" which crops up
frequently when professional electrical engineers are discussing
installations. However, for everyone else, it requires
clarification. I'm not an electrician, so I have no idea when you
use that term whether you're referring to *short circuit* current
or *earth leakage* current or something else altogether (unless you
use an example as you did above but even that's not watertight).
And then there's that lot that read this through Homeownershub -
God only knows what *they* make of it. ;-


The electrical wiring regs' meaning of 'fault' is a hard zero ohm L-N
short..

or L-E

John uses that meaning. Those of us that are more into
repairing things tend to use 'fault' to mean any failure to operate
correctly. The I with some Es seems to like to define existing terms
differently to everyone else, classic communication poor practice.

Being one who also repairs stuff, I am fully aware that the colloquial
use of "fault" is far less specific than that when used in engineering
and standards documentation for electrical systems. However if you are
going to have a meaningful discussion on fusing etc, it is quite
important that everyone uses a consistent set of terms when it matters.

So sure, I am quite happy to agree that my radio may have a fault
because it can no longer receive FM, or the computer PSU has a fault due
to too much ripple on the 5V rail - but you do need a way of describing
and differentiating between when something has gone badly wrong and a
device is now trying to ingest the full output of the local substation,
Vs. its taking an amp and should only be drawing 50mA.


--
Cheers,

John.

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

In article ,
Scott wrote:
Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

And it failed miserably. If a fuse blows, all the vast majority will do is
replace it to get it working again. And are very unlikely to have all
those values to hand. And the spares they are likely to find, 13 amp.

Hence the current method of having wiring capable of taking out a 13 amp
fuse if there is a sort somewhere without causing a fire. And protecting
the device itself with its own fuse if needed.

--
*Why don't sheep shrink when it rains?

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

On Tuesday, 18 August 2020 00:09:20 UTC+1, John Rumm wrote:
On 17/08/2020 22:09, tabbypurr wrote:
On Monday, 17 August 2020 21:57:17 UTC+1, John Rumm wrote:
On 17/08/2020 16:59, Scott wrote:

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10
and 13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They
will all handle fault currents.

When the BS1362 plug system was introduced in '47 the plug fuse was
normally the appliance overload fuse, appliances mostly had little or
more often no other overload failure protection.

Agreed - hence why I mentioned it.

However a good deal of appliances (even then) don't actually need any
overload protection... So there is a danger that you could cause more
problems in the quest for "safety". (i.e. nuisance fuse blows, plugs
running warmer etc).

those aren't dangers. And putting a 3A fuse on a 2A load does not cause nuisance trips.


That has changed of
course, but there are still millions of appliances that have no
built-in overload protection and could benefit from it safety-wise.

I don't have a source of figures for how many are still out there. Do
you? Some, sure; millions perhaps?

I don't have a record of where they figures came from. But it's easy to come up with a very rough idea of the size of the issue.
1. How many substandard appliances have major retail sites sold?
2. How many PAT fail appliances are there per site? What proportion need & lack overload protection.
3. How many historic appliances are still in use? If you find just one per 63 people that's a million.


NT

On Tuesday, 18 August 2020 00:33:28 UTC+1, John Rumm wrote:
On 17/08/2020 22:09, Scott wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

Whatever you call it, if there is only 2 amps of it instead of 13 amps
nothing will convince me that is not safer.

Define safer?

define waste of time

So if your life support system were to fail with a blown fuse when there
is a mains spike because some well meaning but uninformed person
replaced the manufacture fitted 13A fuse with a 2A one "because its
safer", that would be better?

With respect 99.999% of appliances are not life support. That different safety issues apply to that miniscule percentage is not news.


Think it though logically, what are you trying to achieve? Say you have

more safety

a table lamp that takes a single B22 fitting lamp. What is the highest
power lamp that it will take in that format? 250W or about an amp? Is
there any way a lamp could draw say 2kW for a sustained period to put
its flex at risk of dangerous overheating? The answer is not really (at
least not without determined and conscious action by the user to be a
complete numpty).

Now you say, ah but, its a lamp, 3A fuse is better... in a sense you are
right, there is no downsize other than needing to replace the one fitted
by the manufacturer. But what have you actually achieved? The thing that
does matter (i.e. power gets swiftly disconnected when you stick your
chair leg down on the flex and cause a short circuit), will happen
regardless of fuse rating, since you have say 100A of fault current to
play with[1].

You're barking at nonexistent shadows there. Any appliance can get a smouldering insulator fault that takes 3A but not 13A. That's one way appliances catch fire.


Now there are some appliances that do have overload failure modes. If

any insulator can fail smouldering. All appliances include insulation.


they are old enough, they may not include their own protection, for

many modern ones don't either as your tablelamp example shows


those, yes its important they are fitted with the "right" fuse. For

ah, we agree after all


others it matters less than many worry about.

[1] 100A should be a fusing time well under 0.1 secs on a 13A fuse. So
for a PVC flex we can work out the conductor size required to cope with
the I^2 . t let through energy with the adiabatic equation:

s = sqrt( 100 ^ 2 x 0.1 ) / 115 = 0.27mm minimum CSA

(115 being the k factor for PVC insulated cable)

So even the smallest typical 0.5mm^2 CSA flex would be fine with any fuse.

Yup. But the chinese flea bay special with copper coated steel mains lead would catch fire. Proper flex that's partway broken also would not cope, and that is not a rare failure mode.


NT

On Tuesday, 18 August 2020 00:57:27 UTC+1, John Rumm wrote:
On 17/08/2020 23:04, tabbypurr wrote:
On Monday, 17 August 2020 22:29:49 UTC+1, Cursitor Doom wrote:

You frequently use the term "fault current" which crops up
frequently when professional electrical engineers are discussing
installations. However, for everyone else, it requires
clarification. I'm not an electrician, so I have no idea when you
use that term whether you're referring to *short circuit* current
or *earth leakage* current or something else altogether (unless you
use an example as you did above but even that's not watertight).
And then there's that lot that read this through Homeownershub -
God only knows what *they* make of it. ;-


The electrical wiring regs' meaning of 'fault' is a hard zero ohm L-N
short..

or L-E

John uses that meaning. Those of us that are more into
repairing things tend to use 'fault' to mean any failure to operate
correctly. The I with some Es seems to like to define existing terms
differently to everyone else, classic communication poor practice.

Being one who also repairs stuff, I am fully aware that the colloquial
use of "fault" is far less specific than that when used in engineering
and standards documentation for electrical systems.

No, the usage of 'fault' to mean zero ohm short only is specific to UK wiring regs not specific to engineering.


However if you are
going to have a meaningful discussion on fusing etc, it is quite
important that everyone uses a consistent set of terms when it matters.

Good luck with that


So sure, I am quite happy to agree that my radio may have a fault
because it can no longer receive FM, or the computer PSU has a fault due
to too much ripple on the 5V rail - but you do need a way of describing
and differentiating between when something has gone badly wrong and a
device is now trying to ingest the full output of the local substation,
Vs. its taking an amp and should only be drawing 50mA.

On Tuesday, 18 August 2020 10:55:44 UTC+1, Dave Plowman (News) wrote:
In article ,
Scott wrote:

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

And it failed miserably.

On the contrary it was much more effective than the prior system


If a fuse blows, all the vast majority will do is
replace it to get it working again.

which is fine


And are very unlikely to have all
those values to hand. And the spares they are likely to find, 13 amp.

IME most people had 3A & 13A.


Hence the current method of having wiring capable of taking out a 13 amp
fuse if there is a sort somewhere without causing a fire. And protecting
the device itself with its own fuse if needed.

Yup. But historically it did work a lot better than the old 2/5/15A system.


NT

On Tue, 18 Aug 2020 10:51:29 +0100, "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

And it failed miserably. If a fuse blows, all the vast majority will do is
replace it to get it working again. And are very unlikely to have all
those values to hand. And the spares they are likely to find, 13 amp.

Hence the current method of having wiring capable of taking out a 13 amp
fuse if there is a sort somewhere without causing a fire. And protecting
the device itself with its own fuse if needed.

IMO changing to a 2 amp fuse can only nudge safety in one direction.

On 17/08/2020 21:59, John Rumm wrote:
On 17/08/2020 19:11, Cursitor Doom wrote:
On Mon, 17 Aug 2020 09:05:13 -0700 (PDT), wrote:

On Monday, 17 August 2020 16:59:34 UTC+1, ScottÂ* wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:


If it were a BS1362 style fuse, the looking a bit to the left of
the 3A
fuse curve would suggest that it might take 3A indefinitely:

http://wiki.diyfaq.org.uk/images/d/d...FusingTime.png


Yeah, here's a picture of the exact type he


https://images-na.ssl-images-amazon...._AC_SX355_.jpg


Probably fake - the end caps look too shiny to be Bussman

Here are some tell tails:

https://www.pat-testing-training.net...fake-fuses.php

(there is also more to a fuse than will it blow at an appropriate
level
of overload. Actually having the capacity to interrupt the flow of
current, and not exploding in your face being some important ones!)

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than
a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.Â* I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties.Â* How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

2A fuses are certainly a little safer on low current loads, but they
do not limit fault current, they merely trip faster at a given
current & are thus less likely to permit a fire to start. They also
have more chance of tripping before fire on an overheat overcurrent
condition.


What's not to like about that? When a 13A fuse blows, it can release a
*lot* of energy and cause flame damage to surrounding surfaces.
Not to mention quite an alarming bang!

Not with a BS1362 compliant fuse - they should quench any arc and keep
it contained in the fuse.






Having blown 13 amp BS1362 fuses in the past, whatever I was doing that
caused the fuse to blow, drowned out any noise the latter might have
made.

On 18/08/2020 11:41, wrote:
On Tuesday, 18 August 2020 00:33:28 UTC+1, John Rumm wrote:
On 17/08/2020 22:09, Scott wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:

On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:

On 17/08/2020 14:04, Cursitor Doom wrote:
On Mon, 17 Aug 2020 02:12:17 +0100, John Rumm
wrote:

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.

Whatever you call it, if there is only 2 amps of it instead of 13 amps
nothing will convince me that is not safer.

Define safer?

define waste of time

An elderly person getting ripped off after a blown fuse is 'diagnosed'
as a non-repairable item.

So if your life support system were to fail with a blown fuse when there
is a mains spike because some well meaning but uninformed person
replaced the manufacture fitted 13A fuse with a 2A one "because its
safer", that would be better?

With respect 99.999% of appliances are not life support. That different safety issues apply to that miniscule percentage is not news.



Most (many) domestic fires these days are caused by fake chargers and
/or rechargeable devices, including genuine ones that were not fakes.

Wibbling about fuses doesn't seem to be relevant to these.

You can include Soviet colour TV's in that group, but not our problem,
though Hotpoint/Beko white goods are, even though they are fitted with
the 'correct' fuse.