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#1
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Are 3A plug fuses really necessary? Why not always 13A?
Not my question, or belief, but found here...
http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. |
#2
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Are 3A plug fuses really necessary? Why not always 13A?
David Robinson wrote:
Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? It depends on the cross sectional area of the cable cores. As is correctly pointed out in the thread, the fuse is to protect against cable faults, not internal faults in the box. If the cores are too small, a 13 A fuse may not blow or carry enough current to rapidly trip the MCB, leading to a cable that at the best is going to melt the insulation, and at worst may start a fire. -- Tciao for Now! John. |
#3
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 18:50, John Williamson wrote:
It depends on the cross sectional area of the cable cores. As is correctly pointed out in the thread, the fuse is to protect against cable faults, not internal faults in the box. If the cores are too small, a 13 A fuse may not blow or carry enough current to rapidly trip the MCB, leading to a cable that at the best is going to melt the insulation, and at worst may start a fire. Just anecdotally, I had a decorator in my house using a steam stripper. He asked to borrow an extension lead, and I conscientiously checked the extension lead was man enough for the job, then left him to it. Half an hour later, the power went off. Investigating, I found that he hadn't bothered to unreel more of the extension cable than he needed to reach the job - despite clear instructions on the reel to that effect. The entire lot inside the reel had melted, and the power went off when the cores touched. This was a man who had been doing this sort of work for over 10 years, mind. |
#4
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 20:19, GB wrote:
On 07/11/2012 18:50, John Williamson wrote: It depends on the cross sectional area of the cable cores. As is correctly pointed out in the thread, the fuse is to protect against cable faults, not internal faults in the box. If the cores are too small, a 13 A fuse may not blow or carry enough current to rapidly trip the MCB, leading to a cable that at the best is going to melt the insulation, and at worst may start a fire. Just anecdotally, I had a decorator in my house using a steam stripper. He asked to borrow an extension lead, and I conscientiously checked the extension lead was man enough for the job, then left him to it. Half an hour later, the power went off. Investigating, I found that he hadn't bothered to unreel more of the extension cable than he needed to reach the job - despite clear instructions on the reel to that effect. The entire lot inside the reel had melted, and the power went off when the cores touched. This was a man who had been doing this sort of work for over 10 years, mind. Have to admit I have done the same. Stripper well within reels capability but it cut out after a while. My reel has an overheat cut-out fortunately. Lesson learned for all types of wiring. If I take anything bought in Spain back to the UK I will have to change the plug or use it through a correctly fused adaptor. Using them unfused on a 30A ring main could be a recipe for disaster. Worries me sightly that lamps and other itmes out here with thin flex plug into fairly highly rated power sockets. |
#5
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson
wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables A Dell PC with a 5A fuse in the plug A Cisco router with a 10A fuse A Brother laser printer with 13A fuse. Of course this might now create issues with interchangability. I would be interested to see your comments about the above. -- Graham. %Profound_observation% |
#6
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Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote:
Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Old appliances are another matter, and many are not properly protected by a 13A fuse. So its better to keep using 3A where suitable. NT |
#7
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Are 3A plug fuses really necessary? Why not always 13A?
John Williamson wrote:
David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? It depends on the cross sectional area of the cable cores. As is correctly pointed out in the thread, the fuse is to protect against cable faults, not internal faults in the box. If the cores are too small, a 13 A fuse may not blow or carry enough current to rapidly trip the MCB, leading to a cable that at the best is going to melt the insulation, and at worst may start a fire. I am sure that some boiler installation manuals state the use of a 3A fuse - and there is no legal reason why a boiler cannot be powered using a plug and unswitched socket...... -- Adam |
#8
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Are 3A plug fuses really necessary? Why not always 13A?
David Robinson wrote:
Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. 13A fuses can go with a right bang, frightening old ladies. 3A fuses are nicer. Bill |
#10
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote:
All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. That would be interesting. The big bad assumption made in the digital spy thread was to assume only short circuit faults and that massive currents will flow. In that particular case there is little difference between a 3A or 13A fuse. However if the short circuit current is only high, maybe limited by weak spring tension in the fuse holder, corosion of the holdler/fuse cap, dodgy wire termination some where, and say only 20A is flowing. Thene there is a significant difference between a 3A and 13A fuse. -- Cheers Dave. |
#11
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 19:19:33 +0000, GB wrote:
Investigating, I found that he hadn't bothered to unreel more of the extension cable than he needed to reach the job - despite clear instructions on the reel to that effect. The entire lot inside the reel had melted, and the power went off when the cores touched. This was a man who had been doing this sort of work for over 10 years, mind. And was his comment "That's odd. The last time I used a cable reel like that one, the same thing happened". I hope he paid for a replacement. -- Cheers Dave. |
#12
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/12 21:40, Dave Liquorice wrote:
On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote: All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. That would be interesting. The big bad assumption made in the digital spy thread was to assume only short circuit faults and that massive currents will flow. In that particular case there is little difference between a 3A or 13A fuse. However if the short circuit current is only high, maybe limited by weak spring tension in the fuse holder, corosion of the holdler/fuse cap, dodgy wire termination some where, and say only 20A is flowing. Thene there is a significant difference between a 3A and 13A fuse. Or more to the point, under overcurrent, which would you rather have go? a thin piece of flex with plastic insulation lying over a newspaper, or a fuse in a plug. -- Ineptocracy (in-ep-toc-ra-cy) €“ a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers. |
#13
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Counter to what? Frank1 is obviously missing a clue. grahamthompson and Nigel Goodwin seem to have explained more than adequately. Its easy enough to check. From the BS7671:2008 table 41.3[1], the maximum earth loop impedance for a circuit protected by a B32 MCB is 1.44 ohms. That is what gives a fault current on the longest path of the circuit of around 160A - or enough to open a B32 MCB on the "instant" part of its trip response. So we could take that as an example of the minimum fault current the flex will need to withstand when someone shorts it. Lets say the appliance has a flex with 0.5mm^2 CSA conductors. For a short flex (i.e. typically 1.8m) you can ignore the additional resistance of the flex, so can just assume the prospective fault current of 160A. Now that should open a 13A fuse in less than 0.1 secs (probably significantly less). So all you need to know is, will the flex will carry that fault current for long enough to allow the fuse to do its stuff without either vaporising or bursting into flames. So we can work out the minimum size (s) of conductor required for that with the adiabatic equation[2] and the PVC cable type k value of 115. s = sqrt( 160^2 x 0.1 ) / 115 s = 0.44mm^2 Which is less that the actual flex CSA of 0.5mm^2, so in this particular example the flex would actually be adequately protected by the 32A MCB at the origin of the circuit (although the fuse will probably open before the MCB gets a chance to operate) If you try that sum on a shorter circuit - or one with a lower Ze, then you may get an ELI of say 0.5 ohms at the end of the flex. That gives a fault current of 460A which would need a conductor size of aver 1mm^2 to be protected by the main MCB, so here the fuse would be essential. (if the circuit were protected by a BS3036 rewireable fuse, or the circuit a tad out of spec, the flex longer or thinner etc then the fuse in the plug would be essential). [1] http://wiki.diyfaq.org.uk/index.php?...Loop_Impedance [2] http://wiki.diyfaq.org.uk/index.php?...abatic _Check -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#14
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 18:40, David Robinson wrote:
Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. -- Regards Peter Crosland |
#15
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 20:20, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) A Dell PC with a 5A fuse in the plug A Cisco router with a 10A fuse A Brother laser printer with 13A fuse. Of course this might now create issues with interchangability. I would be interested to see your comments about the above. For stuff running with "normal" IEC leads its does not make any real difference. The appliance will have an internal fuse if it needs it, and the cables are quite sturdy (assuming they are not Chinese knock offs!) The kit will have been designed to run safely on 16A circuits with no plug fuse (as it will need to in most countries) so the flex will be specced to suit. IME leads for IT kit doe get swapped about without any regard for their rating (most people have not even spotted there are two different specs of lead and fuse). So 3A fusing may be pushing your luck depending on what it gets connected to. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#16
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 21:40, Dave Liquorice wrote:
On Wed, 07 Nov 2012 20:47:53 +0000, polygonum wrote: All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. That would be interesting. The big bad assumption made in the digital spy thread was to assume only short circuit faults and that massive currents will flow. In that particular case there is little difference between a 3A or 13A fuse. However if the short circuit current is only high, maybe limited by weak spring tension in the fuse holder, corosion of the holdler/fuse cap, dodgy wire termination some where, and say only 20A is flowing. Thene there is a significant difference between a 3A and 13A fuse. If there is only 20A of fault current, then there is 11.5 ohms of resistance somewhere! The 4kW you are dissipating in the fuse holder might be more of a worry than whatever is going on with the flex ;-) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#17
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 20:41, Bill Wright wrote:
David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. 13A fuses can go with a right bang, frightening old ladies. 3A fuses are nicer. You want to see the bang with the counterfeit ones arriving with your latest mains lead from China via ebay: http://s833.beta.photobucket.com/use...tFuse.mp4.html or http://www.bs1363.org.uk/counterfeit_fuse.mpeg -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#18
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 22:34:50 +0000, John Rumm
wrote: On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) Damn. that will teach me to proof read my own regurgitated words. In the original thread you quipped: "You can see why SATA became popular if the IDE leads were that size" -- Graham. %Profound_observation% |
#19
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Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote:
On 07/11/2012 20:33, wrote: On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Old appliances are another matter, and many are not properly protected by a 13A fuse. So its better to keep using 3A where suitable. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. Unfortuately no, I've not kept any notes of those points. One thing it has changed is the minimum permissible conductor cross section in appliance leads, if you look at appliances from the 50s and 60s, some shavers & clocks etc have very thin conductors. Now all new flexes need to be able to survive the i squared t of a 13A fuse blow. NT |
#20
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland
wrote: On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. In the early days of colour TV I was told by a TV engineer that the correct plug fuse for a CTV was 7A to allow for the switch-on current surge of the degaussing circuitry. I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. In fact, was there not also a 1A BS1362 fuse, used for clock plugs, but not shaver adaptors (or was it the other way round?)? -- Frank Erskine |
#21
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 23:55, wrote:
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote: On 07/11/2012 20:33, wrote: On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Old appliances are another matter, and many are not properly protected by a 13A fuse. So its better to keep using 3A where suitable. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. Unfortuately no, I've not kept any notes of those points. One thing it has changed is the minimum permissible conductor cross section in appliance leads, if you look at appliances from the 50s and 60s, some shavers & clocks etc have very thin conductors. Now all new flexes need to be able to survive the i squared t of a 13A fuse blow. NT Heigh-ho. Anyone else know? -- Rod |
#22
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 22:44:35 +0000, John Rumm
wrote: On 07/11/2012 20:41, Bill Wright wrote: David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. 13A fuses can go with a right bang, frightening old ladies. 3A fuses are nicer. You want to see the bang with the counterfeit ones arriving with your latest mains lead from China via ebay: http://s833.beta.photobucket.com/use...tFuse.mp4.html or http://www.bs1363.org.uk/counterfeit_fuse.mpeg I assure you there was no dummy fuse in the adapter I got with a handheld transceiver from China recently. http://www.flickr.com/photos/g3zvt/8...ream/lightbox/ The strange thing was that the charger supplied had a Euro plug, so didn't fit this adapter anyway. The black sleeving on the pins appears to be thin heatshrink that I could easily pick odd with a fingernail. I wonder what internal protection a wall-wart with a Euro or Stucco pins has to have compared to one with our 13A pins? Without an x-ray machine, you've only got their word that they are safe, and they are not only at the mercy of a 32A MCB. -- Graham. %Profound_observation% |
#23
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Are 3A plug fuses really necessary? Why not always 13A?
On Wed, 07 Nov 2012 23:56:09 +0000, Frank Erskine
wrote: On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland wrote: On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. In the early days of colour TV I was told by a TV engineer that the correct plug fuse for a CTV was 7A to allow for the switch-on current surge of the degaussing circuitry. I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. In fact, was there not also a 1A BS1362 fuse, used for clock plugs, but not shaver adaptors (or was it the other way round?)? If I just reach in this drawer... http://www.flickr.com/photos/g3zvt/8...ream/lightbox/ -- Graham. %Profound_observation% |
#24
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Are 3A plug fuses really necessary? Why not always 13A?
polygonum wrote:
On 07/11/2012 23:55, wrote: On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote: On 07/11/2012 20:33, wrote: On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Old appliances are another matter, and many are not properly protected by a 13A fuse. So its better to keep using 3A where suitable. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. Unfortuately no, I've not kept any notes of those points. One thing it has changed is the minimum permissible conductor cross section in appliance leads, if you look at appliances from the 50s and 60s, some shavers & clocks etc have very thin conductors. Now all new flexes need to be able to survive the i squared t of a 13A fuse blow. NT Heigh-ho. Anyone else know? It was around the time the voltages were harmonised at 230V, flexes were marked HAR and CE marking came in. 1995? |
#25
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Are 3A plug fuses really necessary? Why not always 13A?
On 07/11/2012 23:11, Graham. wrote:
On Wed, 07 Nov 2012 22:34:50 +0000, John Rumm wrote: On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) Damn. that will teach me to proof read my own regurgitated words. In the original thread you quipped: "You can see why SATA became popular if the IDE leads were that size" Lol, which to be fair I had completely forgotten about until your comment prompted me to search for it (well it was 18 months ago!) Still nice to know that even of my memory is going I am still consistent (or predictable!) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#26
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Are 3A plug fuses really necessary? Why not always 13A?
In article ,
Frank Erskine wrote: On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland wrote: On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. In the early days of colour TV I was told by a TV engineer that the correct plug fuse for a CTV was 7A to allow for the switch-on current surge of the degaussing circuitry. I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. In fact, was there not also a 1A BS1362 fuse, used for clock plugs, but not shaver adaptors (or was it the other way round?)? clock plugs use a smaller fuse. They are 19mm long as opposed to 1" for BS1362. CPC stock 1A,2A,3A,5A,7A,10A & 13A in BS1362 size -- From KT24 Using a RISC OS computer running v5.18 |
#27
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Are 3A plug fuses really necessary? Why not always 13A?
On Nov 7, 10:26*pm, Peter Crosland wrote:
On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. That's about the size of it. Years ago a "Euro-plug" was designed. It had no fuse and was a throwback to the fifteen amp plugs we had nicely got rid of. I think it was sixteen amp. Fortunately it was abandoned. MK actually started making them. I think the 13a plug is the only one in the world with a fuse. There was another where the fuse was a screw-in pin on the plug. Haven't seen one for years. |
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Are 3A plug fuses really necessary? Why not always 13A?
Dave Liquorice wrote:
However if the short circuit current is only high, maybe limited by weak spring tension in the fuse holder, corosion of the holdler/fuse cap, dodgy wire termination some where, and say only 20A is flowing. Thene there is a significant difference between a 3A and 13A fuse. Exactly. Like in the house I was working at this week. the best earth fault loop reading I could get on the 30A fused socket outlets was 5.6 ohms.The worst, 9ohms. At the 'best' socket, with 5.6 ohms, at the measured voltage of 247V, it would be passing 44 amps, which just wouldnt break the fusebox fuse. At the worst socket, it would be passing 27 Amps, which may break a 13A fuse, but I doubt it would do it in 0.4 of a second, more like a second, which is enough to kill. A 3A fuse would break it immediately (well, ok, in less than half a second). The fuse in the fusebox will be happlily buzzing away, passing the current for half an hour before it broke. The figures were likely to be worse in the evening, as other people came home, and the voltage may drop a little, allowing more current through. Ok, thats an extreme example, but a true one, so the final fuse rating can have safety implications, hence best to put the lowest rating possible in. Alan. -- To reply by e-mail, change the ' + ' to 'plus'. |
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Are 3A plug fuses really necessary? Why not always 13A?
On Nov 7, 10:35*pm, John Rumm wrote:
On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) A Dell PC with a 5A fuse in the plug A Cisco router with a 10A fuse A Brother laser printer with 13A fuse. Of course this might now create issues with interchangability. I would be interested to see your comments about the above. For stuff running with "normal" IEC leads its does not make any real difference. The appliance will have an internal fuse if it needs it, and the cables are quite sturdy (assuming they are not Chinese knock offs!) The kit will have been designed to run safely on 16A circuits with no plug fuse (as it will need to in most countries) so the flex will be specced to suit. IME leads for IT kit doe get swapped about without any regard for their rating (most people have not even spotted there are two different specs of lead and fuse). So 3A fusing may be pushing your luck depending on what it gets connected to. -- Cheers, John. /================================================== ===============\ | * * * * *Internode Ltd - *http://www.internode.co.uk* * * * * *| |-----------------------------------------------------------------| | * * * *John Rumm - john(at)internode(dot)co(dot)uk * * * * * * *| \================================================= ================/ Not all faults are dead shorts. Transformer overheat/burnout for example. Not all equipment has internal fuses. 3Kw/13a of sustained energy in an electronic device/small electric motor could start a nice little fire. |
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Are 3A plug fuses really necessary? Why not always 13A?
On Nov 7, 11:56*pm, Frank Erskine
wrote: On Wed, 07 Nov 2012 22:26:06 +0000, Peter Crosland wrote: On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate.. In the early days of colour TV I was told by a TV engineer that the correct plug fuse for a CTV was 7A to allow for the switch-on current surge of the degaussing circuitry. I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. In fact, was there not also a 1A BS1362 fuse, used for clock plugs, but not shaver adaptors (or was it the other way round?)? -- Frank Erskine There was indeed. One was physically smaller than the plug fuse. You found them in mains electric clock connectors. Of course, you never see mains clocks any more except as radios. There have been all sorts of odd sizes over the years. |
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Are 3A plug fuses really necessary? Why not always 13A?
:
On Wednesday, November 7, 2012 8:47:55 PM UTC, polygonum wrote: On 07/11/2012 20:33, wrote: On Wednesday, November 7, 2012 6:40:34 PM UTC, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. All modern appliances and leads are required to be safe with a 13A fuse. However the reality is that fires do happen, and there are at least some faults where a 3A would blow before a 13A, so maybe preventing a small percentage of fires. Old appliances are another matter, and many are not properly protected by a 13A fuse. So its better to keep using 3A where suitable. Please can you provide a reference to when that changed? And, ideally, what the requirements actually are - in an accessible form. Unfortuately no, I've not kept any notes of those points. One thing it has changed is the minimum permissible conductor cross section in appliance leads, if you look at appliances from the 50s and 60s, some shavers & clocks etc have very thin conductors. Now all new flexes need to be able to survive the i squared t of a 13A fuse blow. I remember those thin leads. My '60s soldering iron had a lead about half the diameter of (today's!) CAT5 patch cables. My assumption up until now has been that globalisation has resulted in all leads being designed for the unfused plugs used in most of the world outside the UK. -- Mike Barnes |
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Are 3A plug fuses really necessary? Why not always 13A?
On Thursday, November 8, 2012 7:43:36 AM UTC, harry wrote:
On Nov 7, 10:26 pm, Peter Crosland wrote: Only the terminally stupid would use a 13A fuse when a 3A is appropriate. That's about the size of it. Years ago a "Euro-plug" was designed. It had no fuse and was a throwback to the fifteen amp plugs we had nicely got rid of. I think it was sixteen amp. Fortunately it was abandoned. MK actually started making them. I think the 13a plug is the only one in the world with a fuse. There was another where the fuse was a screw-in pin on the plug. Haven't seen one for years. Optional mains plug fuses were in use a century ago in the UK, but they were open wire links in plugs that were often wooden. They were banned in 1913 as a fire risk. NT |
#33
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Are 3A plug fuses really necessary? Why not always 13A?
In article
, harry wrote: On Nov 7, 10:26 pm, Peter Crosland wrote: On 07/11/2012 18:40, David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Only the terminally stupid would use a 13A fuse when a 3A is appropriate. That's about the size of it. Years ago a "Euro-plug" was designed. It had no fuse and was a throwback to the fifteen amp plugs we had nicely got rid of. I think it was sixteen amp. Fortunately it was abandoned. MK actually started making them. do you mean the CEEform plug? MK Commando, etc. Very much in use. I think the 13a plug is the only one in the world with a fuse. some of our old 5A round pin plugs had fuses. Perhasp they still do in India. There was another where the fuse was a screw-in pin on the plug. Haven't seen one for years. those were made by D&S. -- From KT24 Using a RISC OS computer running v5.18 |
#34
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Are 3A plug fuses really necessary? Why not always 13A?
On 08/11/2012 07:52, harry wrote:
On Nov 7, 10:35 pm, John Rumm wrote: On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) A Dell PC with a 5A fuse in the plug A Cisco router with a 10A fuse A Brother laser printer with 13A fuse. Of course this might now create issues with interchangability. I would be interested to see your comments about the above. For stuff running with "normal" IEC leads its does not make any real difference. The appliance will have an internal fuse if it needs it, and the cables are quite sturdy (assuming they are not Chinese knock offs!) The kit will have been designed to run safely on 16A circuits with no plug fuse (as it will need to in most countries) so the flex will be specced to suit. IME leads for IT kit doe get swapped about without any regard for their rating (most people have not even spotted there are two different specs of lead and fuse). So 3A fusing may be pushing your luck depending on what it gets connected to. Not all faults are dead shorts. Transformer overheat/burnout for example. For the purposes of this discussion they are (its in the definition of "fault current") Transformers are unlikely to be able to present any sustained load above their design maximum for long - the wire size on their primary winding will typically be *significantly* thinner than that of the supply flex. Not all equipment has internal fuses. If it needs overload protection then it is required to have its own protection. Remember in most markets, protection via a plug fuse is not an option. 3Kw/13a of sustained energy in an electronic device/small electric motor could start a nice little fire. Which would be an overload and not a fault. If there is a plausible overload scenario, then the device in question must include its own protection. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#35
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Are 3A plug fuses really necessary? Why not always 13A?
On Nov 8, 7:52*am, harry wrote:
On Nov 7, 10:35*pm, John Rumm wrote: On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? Indeed - but its not a counter argument. The logic Humax (or whoever) are applying is that the 13A fuse is adequate to protect the flex. That is demonstrably true. However what you say is also true, and in no way conflicts with that. More closely matching the actual size required will mean that when things do go pear shaped, the actual energy let through may be a little lower. Less spark, less heating stress on the cables etc. The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables Strange place to be using a disk interface cable ;-) (IEC perhaps?) A Dell PC with a 5A fuse in the plug A Cisco router with a 10A fuse A Brother laser printer with 13A fuse. Of course this might now create issues with interchangability. I would be interested to see your comments about the above. For stuff running with "normal" IEC leads its does not make any real difference. The appliance will have an internal fuse if it needs it, and the cables are quite sturdy (assuming they are not Chinese knock offs!) The kit will have been designed to run safely on 16A circuits with no plug fuse (as it will need to in most countries) so the flex will be specced to suit. IME leads for IT kit doe get swapped about without any regard for their rating (most people have not even spotted there are two different specs of lead and fuse). So 3A fusing may be pushing your luck depending on what it gets connected to. -- Cheers, John. /================================================== ===============\ | * * * * *Internode Ltd - *http://www.internode.co.uk** * * * *| |-----------------------------------------------------------------| | * * * *John Rumm - john(at)internode(dot)co(dot)uk * * * * * * *| \================================================= ================/ Not all faults are dead shorts. Is it Panto time yet? Oh yes they are. And all short circuits are faults. Anything else is an overload. MBQ |
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Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, November 7, 2012 11:56:12 PM UTC, Frank Erskine wrote:
In the early days of colour TV I was told by a TV engineer that the correct plug fuse for a CTV was 7A to allow for the switch-on current surge of the degaussing circuitry. I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. In fact, was there not also a 1A BS1362 fuse, used for clock plugs, but not shaver adaptors (or was it the other way round?)? 1,2,3,5,7,10 and 13A fuses are all still available. I remember seeing 1A fuses in clock plugs - though some clock plugs used fuses with a different mechanical size just to be awkward... |
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Are 3A plug fuses really necessary? Why not always 13A?
On 08/11/12 10:49, Man at B&Q wrote:
all short circuits are faults. Anything else is an overload. What a peculiar version of the english language you speak... Lets say we have an SMPS, and due to a fault in the main 400V reservoir on the mains side, it starts leaking several amps ... You are saying that's not a fault? -- Ineptocracy (in-ep-toc-ra-cy) €“ a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers. |
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Are 3A plug fuses really necessary? Why not always 13A?
On Thursday, November 8, 2012 10:46:10 AM UTC, John Rumm wrote:
On 08/11/2012 07:52, harry wrote: On Nov 7, 10:35 pm, John Rumm wrote: On 07/11/2012 20:20, Graham. wrote: On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not all faults are dead shorts. Transformer overheat/burnout for example. For the purposes of this discussion they are (its in the definition of "fault current") Welcome to the strange world of Aurthur Brown. The wiring regs use 'fault current' to specifically mean a dead short, but obviously in the real world appliance faults occur that produce current (fault current by definition) that covers the full range from a smallish increase than only overheats a motor to a dead short. Introducing a narrow perspective definition that applies specifically to wiring and using it outside of where it makes good sense is not productive, and insisting it must mean that elsewhere is illogical. In the world of electronics (which many appliances are) fault current does not usually mean a dead short across the mains. Transformers are unlikely to be able to present any sustained load above their design maximum for long - the wire size on their primary winding will typically be *significantly* thinner than that of the supply flex. Not all equipment has internal fuses. If it needs overload protection then it is required to have its own protection. In practice not all has, particularly old appliances Remember in most markets, protection via a plug fuse is not an option. Old UK appliances were typically designed for only the UK market 3Kw/13a of sustained energy in an electronic device/small electric motor could start a nice little fire. Which would be an overload and not a fault. If there is a plausible overload scenario, then the device in question must include its own protection. But in practice a fair few don't. There are still significant numbers of old electrical goods in use spanning the range from pre-95 to 1920s. And not all new goods meet the standards legally required of them. NT |
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Are 3A plug fuses really necessary? Why not always 13A?
On Nov 8, 12:33*pm, The Natural Philosopher
wrote: On 08/11/12 10:49, Man at B&Q wrote: all short circuits are faults. Anything else is an overload. What a peculiar version of the english language you speak... Lets say we have an SMPS, and due to a fault in the main 400V reservoir on the mains side, it starts leaking several amps ... You are saying that's not a fault? Well, it is faulty, but in the jargon, that is not a fault current. MBQ |
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Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, November 7, 2012 8:20:19 PM UTC, Graham. wrote:
On Wed, 7 Nov 2012 10:40:34 -0800 (PST), David Robinson wrote: Not my question, or belief, but found here... http://forums.digitalspy.co.uk/showthread.php?t=1755197 Is there a counter-argument? Thanks, David. Here's a counter argument I made a couple of years ago in response to those that say it's only there to protect the cable. [It] May not be mandated for appliance protection, but isn't it true to say that choosing a plug fuse value sensibly having regard for the maximum current demand of the appliance rather than than just the capability of the cable has always been good practice? The appliance manufactures seem to think so. Take the case of three items I regularly install, all with supplied 0.75mm2 IDE cables A Dell PC with a 5A fuse in the plug That seems OK as few computers would exceed 1kw but if that lead was used as a kettle lead..... A Cisco router with a 10A fuse No idea perhaps they had a lot of 10Amp fuses spare I have, I think they are black, 13Amp brown and 3A red. A Brother laser printer with 13A fuse. In the days ofm teh first laser printers they took quite a heaft startup current, in fact you shouldn;t put laswer printers on sureg protection blaocks either. Not sur eif it's still true as I can't believe the modern USB laserpriners would need a high startup cutrrent.... Of course this might now create issues with interchangability. I would be interested to see your comments about the above. I broguht about 100 "Y" leads that have two IEC sockets on the end and they have 13amp fuses. There's a health and safety notice that says were not allowed to use them as you can't connect two pieces of equipment to one plug.. -- Graham. %Profound_observation% |
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