On Saturday, 24 March 2018 03:16:00 UTC, wrote:
On Friday, 23 March 2018 13:05:57 UTC, whisky-dave wrote:
On Friday, 23 March 2018 01:50:20 UTC, wrote:
On Tuesday, March 20, 2018 at 2:48:07 AM UTC+11, Graham. wrote:

Which is the best fuse to use (3A, 5A or 13A) with a 1.15kW electric fire at a potential difference of 240v
1150/240=4.79 so theoretically a 5A fuse shoud do.
--

Graham.
%Profound_observation%

May be 5A will do, as "cold" heater element resistance would be higher than normal heating.

But according to regulations in the UK on changing fuses it should be either a 3A for below 720W or a 13amp for above 720W .

incorrect.

https://www.rospa.com/home-safety/uk...hoosing-fuses/

ROSPA is not regulations.

Those are the one we have to follow they are part of college regualtions that all plugs were to be fitted with either a 3amp or 13amp fuse NOTHING else was to be used for stabndard lab equipment.

On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into thre appliance.

I hope you jest. But knowing you...


NT

On 20/03/2018 10:04, Dave Plowman (News) wrote:
In article ,
Brian Gaff wrote:
Yes most people who set questions in exams have not experienced the real
world very much has been my suspicion for a while now. They are steeped in
the maths but know little about the real world.

It is the real world which says no new appliance should require a less
than 13 amp fuse in a plug. Because if a lower value blows, many will just
replace it with what is to hand, so likely a 13 amp one.



Well if you do not have a fuse then you cut off the plug, strip the
cables back (earth is optional) place the stripped back cables over the
LN socket terminals (L an N reversal is not a problem) plug in the cut
off plug to allow the stripped off terminals into the socket and make
contact to power....

--
Adam

ARW wrote:

On 20/03/2018 10:04, Dave Plowman (News) wrote:
In article ,
Brian Gaff wrote:
Yes most people who set questions in exams have not experienced the real
world very much has been my suspicion for a while now. They are steeped in
the maths but know little about the real world.

It is the real world which says no new appliance should require a less
than 13 amp fuse in a plug. Because if a lower value blows, many will just
replace it with what is to hand, so likely a 13 amp one.



Well if you do not have a fuse then you cut off the plug, strip the
cables back (earth is optional) place the stripped back cables over the
LN socket terminals (L an N reversal is not a problem) plug in the cut
off plug to allow the stripped off terminals into the socket and make
contact to power....

Which can of course be tested by cautiously touching the stubs of the
wire sticking out of the plug.

--

Roger Hayter

On Monday, 26 March 2018 19:23:40 UTC+1, wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

On Tuesday, 27 March 2018 10:04:31 UTC+1, whisky-dave wrote:
On Monday, 26 March 2018 19:23:40 UTC+1, tabby wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

On Tuesday, 27 March 2018 13:59:54 UTC+1, wrote:
On Tuesday, 27 March 2018 10:04:31 UTC+1, whisky-dave wrote:
On Monday, 26 March 2018 19:23:40 UTC+1, tabby wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

I've not made many statements about electronics what I say is what happens in a student teaching lab.
Current does NOT get pushed out of power supplies a common misunderstanding it seems when studetns go from using a 6V battery to using a PSU set to 6V they are worried it will destroy their circuits because of the higher current rating, I've also had students tell me that their resistor isn't powerful enough.

On 26/03/2018 22:18, Roger Hayter wrote:
ARW wrote:

On 20/03/2018 10:04, Dave Plowman (News) wrote:
In article ,
Brian Gaff wrote:
Yes most people who set questions in exams have not experienced the real
world very much has been my suspicion for a while now. They are steeped in
the maths but know little about the real world.

It is the real world which says no new appliance should require a less
than 13 amp fuse in a plug. Because if a lower value blows, many will just
replace it with what is to hand, so likely a 13 amp one.



Well if you do not have a fuse then you cut off the plug, strip the
cables back (earth is optional) place the stripped back cables over the
LN socket terminals (L an N reversal is not a problem) plug in the cut
off plug to allow the stripped off terminals into the socket and make
contact to power....

Which can of course be tested by cautiously touching the stubs of the
wire sticking out of the plug.

That's why Adam has apprentices!

:-)

On Tuesday, 27 March 2018 13:59:54 UTC+1, wrote:
On Tuesday, 27 March 2018 10:04:31 UTC+1, whisky-dave wrote:
On Monday, 26 March 2018 19:23:40 UTC+1, tabby wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).



As I said before - you are too simplistic!

They figures you give are suggestions/recommendations aimed at the
public, there isn't anything wrong fitting a fuse of a lower rating than
the cable and the 700w/3000w suggestion is only a "rule of thumb". These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php

and

https://www.rospa.com/home-safety/uk...hoosing-fuses/

Also if it were illegal to use other fuse ratings - as you imply - why
is it possible to purchase fuses as shown he

https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem, and 13A for 0.75 sq mm and
above (with a length limit for 0.75 if it's used for certain appliance
ratings)."

As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

Sam

On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).



As I said before - you are too simplistic!

I;'m not the original question was and if it is part of a test for a science foundation course then it should be both correct and simple.


They figures you give are suggestions/recommendations aimed at the
public, there isn't anything wrong fitting a fuse of a lower rating than
the cable and the 700w/3000w suggestion is only a "rule of thumb".

There;s reasons when all you know is the wattgae of the electric fire without knowing anything else about it.

These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php



exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."

NOT a good question for a science foundation course.

and

https://www.rospa.com/home-safety/uk...hoosing-fuses/

Also if it were illegal to use other fuse ratings - as you imply

I've never implied that, what I have said is that you need to follow yuor employers recomendations and T & Cs

and from the PAT testing site, yes our PAT tester uses just 3 amp and 13 amp fuses.

QUOTE "For an appliance rated as 700W or less, a 3A fuse should be fitted. For appliances above 700W, a 13A fuse should be fitted."


So why does it say should be fitted ?

- why
is it possible to purchase fuses as shown he

You can purchase rizzlas, too even the long ones, long spoons on chains, bongs, hunting knives etc...


and its not illegal AFAIK to buy fuses of non standard values, I've even brought 50ma ones.

This year I've brought over 100 1 amp QB fuses and prety much every one of them has blow.



https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.


This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem,

which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W

have and 13A for 0.75 sq mm and
above (with a length limit for 0.75 if it's used for certain appliance
ratings)."

As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

No, emf is volts not current.



Sam

On Wednesday, 28 March 2018 10:33:37 UTC+1, whisky-dave wrote:
On Tuesday, 27 March 2018 13:59:54 UTC+1, tabby wrote:
On Tuesday, 27 March 2018 10:04:31 UTC+1, whisky-dave wrote:
On Monday, 26 March 2018 19:23:40 UTC+1, tabby wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).

you're a hoot!


NT

On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).



As I said before - you are too simplistic!

They figures you give are suggestions/recommendations aimed at the
public, there isn't anything wrong fitting a fuse of a lower rating than
the cable and the 700w/3000w suggestion is only a "rule of thumb". These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php

and

https://www.rospa.com/home-safety/uk...hoosing-fuses/

Also if it were illegal to use other fuse ratings - as you imply - why
is it possible to purchase fuses as shown he

https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem, and 13A for 0.75 sq mm and
above (with a length limit for 0.75 if it's used for certain appliance
ratings)."

As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

Sam

you're talking to a fool.

On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php



exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."

the thinking behind the design of our household electrical system is that the plug fuse is there to protect the cable, and the appliance should either protect itself or be protected by a 13A fuse. However IRL it does more than that for several reasons as I've already covered. Not that you'll listen to sense.


and its not illegal AFAIK to buy fuses of non standard values, I've even brought 50ma ones.

This year I've brought over 100 1 amp QB fuses and prety much every one of them has blow.

so again you don't know how to assess the correct fuse for the job.


https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as 3A fuse for everything upto 699W.


It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.


This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem,

which is why most of our IEC leads have either 5 or 13 amp fueses in them..
£amp is just too low unless yuo are sure you'll never exceed 700W

I thought you said everything there had a 3 or 13A fuse.


As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

No, emf is volts not current.

you're funny. And you seldom learn.


NT

On Wednesday, 28 March 2018 15:22:08 UTC+1, wrote:
On Wednesday, 28 March 2018 10:33:37 UTC+1, whisky-dave wrote:
On Tuesday, 27 March 2018 13:59:54 UTC+1, tabby wrote:
On Tuesday, 27 March 2018 10:04:31 UTC+1, whisky-dave wrote:
On Monday, 26 March 2018 19:23:40 UTC+1, tabby wrote:
On Monday, 26 March 2018 10:41:37 UTC+1, whisky-dave wrote:

feeding an appliance rated at say 2 amps will still be protected by
using a fuse suitable for the appliance.

That wasn't the question, and you don't feed the appliance, thatr's one thing our studetns get wrong too, the appliance takes current , current doesn't get pushed into the appliance.

I hope you jest. But knowing you...

which you don't

we've seen enough of your statements about electronics to know where you're at with that.

So yuo must notice that I post evidence that I am right so far you've shown nothing regarding how to work out what fuse to put in a plug.
If you had any sense yuo could find out via google.

https://www.electricalsafetyfirst.or...ugs-and-fuses/

Quotes
The fuse in a plug is a safety device designed to protect the lead rather than the appliance.

Plugs for appliances rated up to about 700 watts should have a 3-amp fuse (coloured red).

Plugs for appliances rated between about 700 watts and 3000 watts (the maximum rating of a wall socket) should be fitted with a 13-amp fuse (coloured brown).

you're a hoot!


NT

And you can ignore the same facts from many sources what does that make you.

On Wednesday, 28 March 2018 15:31:19 UTC+1, wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php



exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."

the thinking behind the design of our household electrical system is that the plug fuse is there to protect the cable,

Well done at last.

and the appliance should either protect itself or be protected by a 13A fuse.

Yep well done again.


However IRL it does more than that for several reasons as I've already covered.

No you've not

Not that you'll listen to sense.

Show that sense then or stop talking crap.

Look back at the original question, which asked what fuse you'd use for 1115W electric fire. No mention of what lead was connected if it was a piece of 1 amp cable guess what ......


and its not illegal AFAIK to buy fuses of non standard values, I've even brought 50ma ones.

This year I've brought over 100 1 amp QB fuses and prety much every one of them has blow.

so again you don't know how to assess the correct fuse for the job.

That was the correct fuse for the job as the job was to prove to students that even a 1.5V alkaline battery can blow a fuse, its the first labsheet the students do, that's why we provided them with a glass QB fuse so they can see it blow that is the whole point.
They then check the fuse for continuity (I'd like the labsheet to get them to test this before but then I don't write labsheets academics do)

But being the type you appear to be you won't believe me.
So
http://www.engineeringbookspdf.com/m...charles-platt/

page 15 :- How to blow a fuse. fig. 1-35
They use a 3 amp automovite fuses which are far more expensive than the ones I buy. We buy ~60 of these books each year I think that is a waste of money and we should write our own labsheets for the skills course, but the academics seem to like a recommened boook.





https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as 3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly in a test.





It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.


This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem,

which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W

I thought you said everything there had a 3 or 13A fuse.

Only if using a calculation from what's on the back of an appliance.
The majority of our leads are IEC standard with 6 amp cable as standard, on the moulded plug it says stamped/engraved on the plug 5 amp fuse fitted.
These leads aren't kettle leads you do know that don't you.

These leads are used for our soldering irons 100W our bench PSUs 300W, scopes 100W they are used with our PCs and monitors and most of the lab equipment.





As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output



NT

In article 54e0d6af-4379-44ed-8b1a-c583b1544bb1
@googlegroups.com, says...


exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."



Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.



which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W


But as an IEC connector with a suitable cable is rated at 10A
Max, why are you fitting 13A fuses?

Remember, as you said "The purpose of the fuse within a
BS1363 plug is to protect the cable." so you should be fitting
10A fuses, surely?

--

Terry

---
This email has been checked for viruses by AVG.
http://www.avg.com

On Wednesday, 28 March 2018 17:14:13 UTC+1, Terry Casey wrote:
In article 54e0d6af-4379-44ed-8b1a-c583b1544bb1
@googlegroups.com, says...


exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."



Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.



which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W


But as an IEC connector with a suitable cable is rated at 10A
Max, why are you fitting 13A fuses?

I'm not, I haven't any 10amp IEC cables.
I mhave IEC cables that have cable rating of 6 amps and 5 amp fuses.


With equipement which have dedicated leads attached that can't be removed they have whatever fuses they have come with the appliance lead, if the fuse blows then the same value fuse is replaced and the item is stored until it gets tested by our PAT taster, it doesn't get put back into use until they have tested it.

Very few items in the lab have dedicated leads just angle poised lamps and the 2KW radiators, which have 13amp fuses NOT 8.7 amp which I assume you'd use, but no they have 13amp for some reason.





Remember, as you said "The purpose of the fuse within a
BS1363 plug is to protect the cable." so you should be fitting
10A fuses, surely?


https://www.theiet.org/forums/forum/...threadid=31036

The IET sponsers some of our projects here, they send us goodie bags to for teh students who get a free membership, so we do and should follow their giudance where possible.


QUOTE
This has been a source of confusion for many years.

The IEC socket is rated at 10A, but most IEC leads supplied with equipment are fitted with 0.75mm cable, which is (nominally)rated at 6A. Hence, you would expect to see a 5A fuse, and this is what is normally fitted.

However, BS1362 only now recognises 2 values of plug top fuse, stating that a 3A fuse should be fitted to an appliance of less than 700W and a 13A fuse to an appliance bigger.

Consequently, it is not uncommon to find brand new IEC cables fitted with 13A fuses.


Now go argue with the institute of electrical engineers about it.

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output

Explain what a current is, what controls the amount and how it is produced.

On Wed, 28 Mar 2018 09:45:19 -0700, whisky-dave wrote:

Now go argue with the institute of electrical engineers about it.

Or, to give them their 'modern' name (for several years now), The
Institution of Engineering and Technology.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On Wednesday, 28 March 2018 17:46:46 UTC+1, Sam wrote:

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output

Explain what a current is, what controls the amount and how it is produced.

EMF is measured on volts as it says, what controls the amount is the restistance or impedence or reactance. Without a PD or EMF you don't get current.

On Wednesday, 28 March 2018 16:58:21 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1, tabby wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php



exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable.."

the thinking behind the design of our household electrical system is that the plug fuse is there to protect the cable,

Well done at last.

and the appliance should either protect itself or be protected by a 13A fuse.

Yep well done again.


However IRL it does more than that for several reasons as I've already covered.

No you've not

Not that you'll listen to sense.

Show that sense then or stop talking crap.

Look back at the original question, which asked what fuse you'd use for 1115W electric fire. No mention of what lead was connected if it was a piece of 1 amp cable guess what ......


and its not illegal AFAIK to buy fuses of non standard values, I've even brought 50ma ones.

This year I've brought over 100 1 amp QB fuses and prety much every one of them has blow.

so again you don't know how to assess the correct fuse for the job.

That was the correct fuse for the job as the job was to prove to students that even a 1.5V alkaline battery can blow a fuse, its the first labsheet the students do, that's why we provided them with a glass QB fuse so they can see it blow that is the whole point.
They then check the fuse for continuity (I'd like the labsheet to get them to test this before but then I don't write labsheets academics do)

But being the type you appear to be you won't believe me.
So
http://www.engineeringbookspdf.com/m...charles-platt/

page 15 :- How to blow a fuse. fig. 1-35
They use a 3 amp automovite fuses which are far more expensive than the ones I buy. We buy ~60 of these books each year I think that is a waste of money and we should write our own labsheets for the skills course, but the academics seem to like a recommened boook.





https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as 3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly in a test.





It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.


This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem,

which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W

I thought you said everything there had a 3 or 13A fuse.

Only if using a calculation from what's on the back of an appliance.
The majority of our leads are IEC standard with 6 amp cable as standard, on the moulded plug it says stamped/engraved on the plug 5 amp fuse fitted.
These leads aren't kettle leads you do know that don't you.

These leads are used for our soldering irons 100W our bench PSUs 300W, scopes 100W they are used with our PCs and monitors and most of the lab equipment.





As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output



NT

I guess I shouldn't reply to fools.

On 28/03/2018 17:54, whisky-dave wrote:
On Wednesday, 28 March 2018 17:46:46 UTC+1, Sam wrote:

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output

Explain what a current is, what controls the amount and how it is produced.

EMF is measured on volts as it says, what controls the amount is the restistance or impedence or reactance. Without a PD or EMF you don't get current.

You haven't defined what a current is - ie it a flow of electrons.

I always understood that the magnitude of the EMF/PD also controls the
electron flow and hence the current.

Basic formula:

I=E/R

On Wed, 28 Mar 2018 18:11:02 +0100, Sam wrote:

On 28/03/2018 17:54, whisky-dave wrote:
On Wednesday, 28 March 2018 17:46:46 UTC+1, Sam wrote:

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle
{\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the
electrical intensity or "pressure" developed by a source of
electrical energy such as a battery or generator.[2] A device that
converts other forms of energy into electrical energy (a
"transducer") provides an emf at its output

Explain what a current is, what controls the amount and how it is
produced.

EMF is measured on volts as it says, what controls the amount is the
restistance or impedence or reactance. Without a PD or EMF you don't
get current.

You haven't defined what a current is - ie it a flow of electrons.

I always understood that the magnitude of the EMF/PD also controls the
electron flow and hence the current.

Basic formula:

I=E/R

I think that is roughly what he is trying to say. Luckily he isn't a
lecturer.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On Wednesday, 28 March 2018 18:00:37 UTC+1, wrote:
On Wednesday, 28 March 2018 16:58:21 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1, tabby wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

These
sites shows you the possible pitfalls of it:

https://www.pat-testing-training.net...se-ratings.php



exactly as I said
"The purpose of the fuse within a BS1363 plug is to protect the cable."

the thinking behind the design of our household electrical system is that the plug fuse is there to protect the cable,

Well done at last.

and the appliance should either protect itself or be protected by a 13A fuse.

Yep well done again.


However IRL it does more than that for several reasons as I've already covered.

No you've not

Not that you'll listen to sense.

Show that sense then or stop talking crap.

Look back at the original question, which asked what fuse you'd use for 1115W electric fire. No mention of what lead was connected if it was a piece of 1 amp cable guess what ......


and its not illegal AFAIK to buy fuses of non standard values, I've even brought 50ma ones.

This year I've brought over 100 1 amp QB fuses and prety much every one of them has blow.

so again you don't know how to assess the correct fuse for the job.

That was the correct fuse for the job as the job was to prove to students that even a 1.5V alkaline battery can blow a fuse, its the first labsheet the students do, that's why we provided them with a glass QB fuse so they can see it blow that is the whole point.
They then check the fuse for continuity (I'd like the labsheet to get them to test this before but then I don't write labsheets academics do)

But being the type you appear to be you won't believe me.
So
http://www.engineeringbookspdf.com/m...charles-platt/

page 15 :- How to blow a fuse. fig. 1-35
They use a 3 amp automovite fuses which are far more expensive than the ones I buy. We buy ~60 of these books each year I think that is a waste of money and we should write our own labsheets for the skills course, but the academics seem to like a recommened boook.





https://www.esr.co.uk/electronics/fuses-household.htm

I also came across this from a forum:

" The problem is that of "surge" or "startup" currents. These often blow
a 3A fuse.

Yes I know and yet another reason not to use the wattage calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as 3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly in a test.





It;s even a bigger problem with IEC leads of which we have 100s which if just leads are treaded differntly because you have no idea what they will be connected to power wise.


This is why Table 2 of BS1363-1 effectively states that for 0.5 sq mm,
5A fuse may be used if this is a problem,

which is why most of our IEC leads have either 5 or 13 amp fueses in them.
£amp is just too low unless yuo are sure you'll never exceed 700W

I thought you said everything there had a 3 or 13A fuse.

Only if using a calculation from what's on the back of an appliance.
The majority of our leads are IEC standard with 6 amp cable as standard, on the moulded plug it says stamped/engraved on the plug 5 amp fuse fitted.
These leads aren't kettle leads you do know that don't you.

These leads are used for our soldering irons 100W our bench PSUs 300W, scopes 100W they are used with our PCs and monitors and most of the lab equipment.





As for current flow.

The appliance takes/allows the current to flow due to its
resistance/impedance and the source forces/feeds the current to the
appliance. Isn't this is what is implied by EMF of a source, ie the
Electro Motive Force?

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output



NT

I guess I shouldn't reply to fools.

No not when they can show you you are wrong, it make you look a bigger fool..

On Wednesday, 28 March 2018 18:11:07 UTC+1, Sam wrote:
On 28/03/2018 17:54, whisky-dave wrote:
On Wednesday, 28 March 2018 17:46:46 UTC+1, Sam wrote:

No, emf is volts not current.

you're funny. And you seldom learn.

https://en.wikipedia.org/wiki/Electromotive_force

Electromotive force, abbreviated emf (denoted E {\displaystyle {\mathcal {E}}} {\mathcal {E}} and measured in volts),[1] is the electrical intensity or "pressure" developed by a source of electrical energy such as a battery or generator.[2] A device that converts other forms of energy into electrical energy (a "transducer") provides an emf at its output

Explain what a current is, what controls the amount and how it is produced.

EMF is measured on volts as it says, what controls the amount is the restistance or impedence or reactance. Without a PD or EMF you don't get current.

You haven't defined what a current is - ie it a flow of electrons.

which you don't get without a potential differnce.


I always understood that the magnitude of the EMF/PD also controls the
electron flow and hence the current.

Basic formula:

I=E/R

Yes and what is the magnitude of the EMF/PD ?

What is E and R then ?

Electomotive Force (EMF), like pressure pushing on water, or like gravity pulling everything on earth, is what pushes and pulls electrons to cause them to jump from one atom to the next. Electromotive Force is measured in Voltage.

NO VOLTAGE then NO current.

https://physics.stackexchange.com/qu...nce-and-mutual

we ran a lab on this just 2-3 weeks ago.

On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

This year I've brought over 100 1 amp QB fuses and prety much
every one of them has blow.

so again you don't know how to assess the correct fuse for the
job.

That was the correct fuse for the job as the job was to prove to
students that even a 1.5V alkaline battery can blow a fuse, its the
first labsheet the students do, that's why we provided them with a
glass QB fuse so they can see it blow that is the whole point. They
then check the fuse for continuity (I'd like the labsheet to get them
to test this before but then I don't write labsheets academics do)

You must have some really thick students then.

I suppose given that the people who seem to be teaching them can't work
out how to heat their laboratory properly this is hardly surprising.

A fresh AA cell will comfortably source about 10A into a dead short - it
gets warm quite quickly so you better have a fuse in circuit to blow.

Handing out a range of low fuse values so that some would last a bit
longer would be instructive for the students.

But being the type you appear to be you won't believe me. So
http://www.engineeringbookspdf.com/m...charles-platt/

page 15 :- How to blow a fuse. fig. 1-35 They use a 3 amp automovite
fuses which are far more expensive than the ones I buy. We buy ~60 of
these books each year I think that is a waste of money and we should
write our own labsheets for the skills course, but the academics seem
to like a recommened boook.

You buy in course books for laboratory practicals? Cowboys!

" The problem is that of "surge" or "startup" currents. These
often blow a 3A fuse.

Yes I know and yet another reason not to use the wattage
calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

--
Regards,
Martin Brown

Martin Brown wrote:

On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

This year I've brought over 100 1 amp QB fuses and prety much
every one of them has blow.

so again you don't know how to assess the correct fuse for the
job.

That was the correct fuse for the job as the job was to prove to
students that even a 1.5V alkaline battery can blow a fuse, its the
first labsheet the students do, that's why we provided them with a
glass QB fuse so they can see it blow that is the whole point. They
then check the fuse for continuity (I'd like the labsheet to get them
to test this before but then I don't write labsheets academics do)

You must have some really thick students then.

I suppose given that the people who seem to be teaching them can't work
out how to heat their laboratory properly this is hardly surprising.

A fresh AA cell will comfortably source about 10A into a dead short - it
gets warm quite quickly so you better have a fuse in circuit to blow.

Handing out a range of low fuse values so that some would last a bit
longer would be instructive for the students.

But being the type you appear to be you won't believe me. So
http://www.engineeringbookspdf.com/m...-edition-charl
es-platt/

page 15 :- How to blow a fuse. fig. 1-35 They use a 3 amp automovite
fuses which are far more expensive than the ones I buy. We buy ~60 of
these books each year I think that is a waste of money and we should
write our own labsheets for the skills course, but the academics seem
to like a recommened boook.

You buy in course books for laboratory practicals? Cowboys!

" The problem is that of "surge" or "startup" currents. These
often blow a 3A fuse.

Yes I know and yet another reason not to use the wattage
calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

I don't doubt that that was what the examiner was expecting. If the
fire is 1.15kW at 230V (if from EU it could even be 220V) then it would
draw 6A at 253V.


--

Roger Hayter

On Thursday, 29 March 2018 10:48:55 UTC+1, Martin Brown wrote:
On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:
On Wednesday, 28 March 2018 14:58:30 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 14:25:50 UTC+1, Sam wrote:

This year I've brought over 100 1 amp QB fuses and prety much
every one of them has blow.

so again you don't know how to assess the correct fuse for the
job.

That was the correct fuse for the job as the job was to prove to
students that even a 1.5V alkaline battery can blow a fuse, its the
first labsheet the students do, that's why we provided them with a
glass QB fuse so they can see it blow that is the whole point. They
then check the fuse for continuity (I'd like the labsheet to get them
to test this before but then I don't write labsheets academics do)

You must have some really thick students then.

Yep, I've been talking to a couple this morning they admit it, in school most practiacal aren't even demostrated and they don't do practicals at school which is why most of teh oversea studetns are better practically because they still do practicals while here in the UK everything is academical accessed , we as a country don;t value practical skills anymore, it's why we have a shortage of engineers and lots of admin.


I suppose given that the people who seem to be teaching them can't work
out how to heat their laboratory properly this is hardly surprising.

Yes I agree, and as theb weathe rgot worse the administration team emailed everyone to tell us they had decided to go home at 3pm leaving the rest of us techs, academics, students, researchers and everyone else still here.


A fresh AA cell will comfortably source about 10A into a dead short - it
gets warm quite quickly so you better have a fuse in circuit to blow.

And even at 10Amps we can't use these to heat the lab.

Yes well done which is why we run this lab to show such things as students don't even need to use batteries in this modern world most things are rechargable.

You see this is what real teaching is about, its not just about giving them marks out of 10 on a multi-choice sheet.


Handing out a range of low fuse values so that some would last a bit
longer would be instructive for the students.

and that is why we use 1a QB I;ve already suggested we could you ant-surge too but this course unit isn lt about fuses it;s about how to connect things and understanding using protoboard and stripboard amounts other basic things that those from school that have choseen computer science might need to know if they haven't studies or rememered their physics.


But being the type you appear to be you won't believe me. So
http://www.engineeringbookspdf.com/m...charles-platt/

page 15 :- How to blow a fuse. fig. 1-35 They use a 3 amp automovite
fuses which are far more expensive than the ones I buy. We buy ~60 of
these books each year I think that is a waste of money and we should
write our own labsheets for the skills course, but the academics seem
to like a recommened boook.

You buy in course books for laboratory practicals? Cowboys!

Yes I agree, but it does seem thnat some of our academics can't write practicals like they used to, perhaps they do did their degrees in just theory.


" The problem is that of "surge" or "startup" currents. These
often blow a 3A fuse.

Yes I know and yet another reason not to use the wattage
calculation on the back of pieces of equipment.

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps.

Which are used as heaters, they were very popular a few years ago less so now it seems. So why advise people to use this sort of thing to calculate fuse values. ?
and why is c question in a mid-term test for science foundation students.


which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

and he is wrong to state that the fuse should be 5amp.

Back to the OP.

In my day you would have got 5 points for calcualtinbg what raing of
fuse was theretically required and a further 5 for pointing out that
this was in fact irrelevant, as the purpose of the fuse was not to
protect the appliance, but its cable and therefore 13A would be a
standard fitting.




--
€œSome people like to travel by train because it combines the slowness of
a car with the cramped public exposure of €¨an airplane.€�

Dennis Miller

On 29/03/2018 11:23, Roger Hayter wrote:
Martin Brown wrote:

On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

I don't doubt that that was what the examiner was expecting. If the
fire is 1.15kW at 230V (if from EU it could even be 220V) then it would
draw 6A at 253V.

A nominally 5A fuse will sustain a 7A current almost indefinitely so
there is actually no problem in practice. This is the difference between
engineering and just doing the sums mindlessly. You might get extra
points for pointing out that the plug will run warm as a result.

--
Regards,
Martin Brown

In article ,
The Natural Philosopher wrote:
Back to the OP.

In my day you would have got 5 points for calcualtinbg what raing of
fuse was theretically required and a further 5 for pointing out that
this was in fact irrelevant, as the purpose of the fuse was not to
protect the appliance, but its cable and therefore 13A would be a
standard fitting.

That would surely depend on whoever marking it had access to the regs
governing such things and understood them. Not something you could
guarantee.

--
*I couldn't repair your brakes, so I made your horn louder *

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

On Thursday, 29 March 2018 14:09:45 UTC+1, Martin Brown wrote:
On 29/03/2018 11:23, Roger Hayter wrote:
Martin Brown wrote:

On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

I don't doubt that that was what the examiner was expecting. If the
fire is 1.15kW at 230V (if from EU it could even be 220V) then it would
draw 6A at 253V.

A nominally 5A fuse will sustain a 7A current almost indefinitely so
there is actually no problem in practice.

Yes there is because it will get warm, you shouldn't be running ampliances at 6 amps with a 5 amp fuse. Even if an aplliance might reach 5 amps you shouldn't be running it on a 5amp fuse.


This is the difference between
engineering and just doing the sums mindlessly.

yes ignore the mindless sums, that tell you the curretn will be 4.999amps so a 5 amps fuuse will be OK it won't, espeacially if you;re running it using 1amp cable.



You might get extra
points for pointing out that the plug will run warm as a result.

which of course it shouldn't.


--
Regards,
Martin Brown

On Thursday, 29 March 2018 10:21:13 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 18:00:37 UTC+1, tabby wrote:
On Wednesday, 28 March 2018 16:58:21 UTC+1, whisky-dave wrote:

I guess I shouldn't reply to fools.

No not when they can show you you are wrong, it make you look a bigger fool.

no chance of that from you though.

Dave Plowman (News) wrote:

In article ,
The Natural Philosopher wrote:
Back to the OP.

In my day you would have got 5 points for calcualtinbg what raing of
fuse was theretically required and a further 5 for pointing out that
this was in fact irrelevant, as the purpose of the fuse was not to
protect the appliance, but its cable and therefore 13A would be a
standard fitting.

That would surely depend on whoever marking it had access to the regs
governing such things and understood them. Not something you could
guarantee.

But, of course, if they don't understand a subject they should not be
setting examination questions on it. Even if the question is merely
designed to beautify Ohm's law and power calculations.

--

Roger Hayter

Martin Brown wrote:

On 29/03/2018 11:23, Roger Hayter wrote:
Martin Brown wrote:

On 28/03/2018 16:58, whisky-dave wrote:
On Wednesday, 28 March 2018 15:31:19 UTC+1,
wrote:

absolutely the wrong conclusion. It's just not quite as simple as
3A fuse for everything upto 699W.

Exactly so don't use caculations for this sort of thing, especailly
in a test.

The only major exceptions have a very low initial resistance like quartz
halogen lamps which really do have an aggressive switch on surge
current. An 1kW electric fire would work OK with a 5A fuse and is
clearly the answer that the examiner was expecting.

I don't doubt that that was what the examiner was expecting. If the
fire is 1.15kW at 230V (if from EU it could even be 220V) then it would
draw 6A at 253V.

A nominally 5A fuse will sustain a 7A current almost indefinitely so
there is actually no problem in practice. This is the difference between
engineering and just doing the sums mindlessly. You might get extra
points for pointing out that the plug will run warm as a result.

This might be true if plugs were not subject to considerable
accelerations in daily use, being removed and banged on hard things when
hot. I don't think your 5A fuse will last long.

--

Roger Hayter

In article ,
Roger Hayter wrote:
Dave Plowman (News) wrote:

In article ,
The Natural Philosopher wrote:
Back to the OP.

In my day you would have got 5 points for calcualtinbg what raing of
fuse was theretically required and a further 5 for pointing out that
this was in fact irrelevant, as the purpose of the fuse was not to
protect the appliance, but its cable and therefore 13A would be a
standard fitting.

That would surely depend on whoever marking it had access to the regs
governing such things and understood them. Not something you could
guarantee.

But, of course, if they don't understand a subject they should not be
setting examination questions on it. Even if the question is merely
designed to beautify Ohm's law and power calculations.

Not really. OK to set a theoretical question which doesn't take into
account practice. IIRC, the reason not to have a vast range of plug top
fuses these days is that most punters simply don't understand such things
and will just fit what is to hand - usually the most common one, ie 13
amp.

The original question didn't state is was dealing with a fused plug anyway.

--
*The first rule of holes: If you are in one, stop digging!

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

On Thursday, 29 March 2018 17:58:48 UTC+1, wrote:
On Thursday, 29 March 2018 10:21:13 UTC+1, whisky-dave wrote:
On Wednesday, 28 March 2018 18:00:37 UTC+1, tabby wrote:
On Wednesday, 28 March 2018 16:58:21 UTC+1, whisky-dave wrote:

I guess I shouldn't reply to fools.

No not when they can show you you are wrong, it make you look a bigger fool.

no chance of that from you though.

Already done it.