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Are 3A plug fuses really necessary? Why not always 13A?
On Sunday, 20 November 2016 22:39:25 UTC, John Rumm wrote:
Why keep prattling about historic devices, when it has already been accepted by everyone that they are a special case? They have no relevance to current practice. Current plug fusing practice they obviously do. Calling them special cases means pretty much nothing. They are what they are, and some are simply not safe on 13A fuses. End of story. |
Are 3A plug fuses really necessary? Why not always 13A?
On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote:
On 20/11/2016 21:55, tabbypurr wrote: It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing. So grow up and stop doing it then. Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in. |
Are 3A plug fuses really necessary? Why not always 13A?
On Sun, 20 Nov 2016 16:38:47 +0000, John Rumm wrote:
Hence why people should pick the fuse according to power consumption Huh? So you are now expecting a user to 1) recognise that the kit is 40 years old class 0 device with 10m of 0.5mm^2 CSA flex, and now work out what fuse they should put in the extension lead? Good luck with that one. Indeed. Also try a 5A fuse in 1kW vac - fair chance it won't last long. In the '80s a fridge plant installer wanted to know if there were slow/delay fuses for the 13A plug. As he pointed out, having a 13A fuse on a 250W device was a bit OTT. He'd tried lower ratings but, of course, the start took them out. Now, I can't remember the figures, but we put a scope on various motors, from a 4 cu.ft. freezer via a big single phase job and some 3-phase plant. The initial 1 - 2½ cycles are very high for the rating of the motor. I do recall that the little freezer would have, eventually, strained a 10A fuse. -- Peter. The gods will stay away whilst religions hold sway |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
PeterC wrote: Indeed. Also try a 5A fuse in 1kW vac - fair chance it won't last long. In the '80s a fridge plant installer wanted to know if there were slow/delay fuses for the 13A plug. As he pointed out, having a 13A fuse on a 250W device was a bit OTT. He'd tried lower ratings but, of course, the start took them out. Now, I can't remember the figures, but we put a scope on various motors, from a 4 cu.ft. freezer via a big single phase job and some 3-phase plant. The initial 1 - 2½ cycles are very high for the rating of the motor. I do recall that the little freezer would have, eventually, strained a 10A fuse. My first colour telly took out anything other than a 13 amp plug fuse. Despite having the usual weedy twin flex as a mains cable. -- *I don't believe in astrology. I am a Sagittarius and we're very skeptical. Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On 21/11/2016 08:18, PeterC wrote:
On Sun, 20 Nov 2016 16:38:47 +0000, John Rumm wrote: Hence why people should pick the fuse according to power consumption Huh? So you are now expecting a user to 1) recognise that the kit is 40 years old class 0 device with 10m of 0.5mm^2 CSA flex, and now work out what fuse they should put in the extension lead? Good luck with that one. Indeed. Also try a 5A fuse in 1kW vac - fair chance it won't last long. In the '80s a fridge plant installer wanted to know if there were slow/delay fuses for the 13A plug. As he pointed out, having a 13A fuse on a 250W device was a bit OTT. He'd tried lower ratings but, of course, the start took them out. Induction motors in particular are well known for significant inrush. Hence why MCBs with their dual mode protection are better suited than fuses in many cases. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
On 21/11/2016 04:05, wrote:
On Sunday, 20 November 2016 22:39:25 UTC, John Rumm wrote: Why keep prattling about historic devices, when it has already been accepted by everyone that they are a special case? They have no relevance to current practice. Current plug fusing practice they obviously do. Calling them special cases means pretty much nothing. Few people have any of them, even fewer are going to know how to select an appropriate fuse for them. If you have some, and are aware and select the right fuse, good I am pleased for you. For the majority of people buying and using appliances these days, they will come with a fitted plug including a 13A fuse, which will offer adequate fault protection. Chances are they will never need to replace it, and getting anal about swapping it out for a 5A fuse because its "correct" achieves nothing of value. They are what they are, and some are simply not safe on 13A fuses. End of story. Agreed - no one is saying otherwise. Now what has any of that got to do with current practice? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
wrote: On Sun, 20 Nov 2016 18:47:50 +0000 (GMT), "Dave Plowman (News)" wrote: Yes I realise that other leads are available, as I am sure you know full well. I'm sure you might have been able to buy a non 13 amp fused extension lead once. If you can today, I'd like to hear of where. http://www.staging.greenham.com/c/pl...ble-Reel-5-Amp That's a cable reel. The low rating is almost certainly to protect it when used not fully unwound. I'll bet the cable size is sufficient to blow a 13 amp fuse within the rated time in event of a short. -- *Therapy is expensive, poppin' bubble wrap is cheap! You choose. Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
John Rumm wrote: For the majority of people buying and using appliances these days, they will come with a fitted plug including a 13A fuse, which will offer adequate fault protection. Chances are they will never need to replace it, and getting anal about swapping it out for a 5A fuse because its "correct" achieves nothing of value. Whether we like it or not, perhaps the majority haven't a clue about what various appliances take current wise, and care even less. So to prevent misuse and possible injury, all extension leads on sale should be capable of carrying 13 amps without melting. -- *Why doesn't glue stick to the inside of the bottle? Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On Mon, 21 Nov 2016 13:44:28 +0000 (GMT), "Dave Plowman (News)"
wrote: In article , wrote: On Sun, 20 Nov 2016 18:47:50 +0000 (GMT), "Dave Plowman (News)" wrote: Yes I realise that other leads are available, as I am sure you know full well. I'm sure you might have been able to buy a non 13 amp fused extension lead once. If you can today, I'd like to hear of where. http://www.staging.greenham.com/c/pl...ble-Reel-5-Amp That's a cable reel. The low rating is almost certainly to protect it when used not fully unwound. I'll bet the cable size is sufficient to blow a 13 amp fuse within the rated time in event of a short. Well if you want to split hairs between lead and cable one of which happens to be wound on a reel. Perhaps the warning about unwinding fully before use they have written is unnecessary. TBH I wonder what fuse is actually fitted in the plug, enlarging the image shows the plug instruction card to show a 13 amp fuse. I reckon that is what is fitted and it relies on the inbuilt cutout it appears to have judging by the presence of the red button. There is this http://www.screwfix.com/p/carroll-me...mm-x-14m/2458p You didn't say it had to be below 13 amps, just non 13 amp. G.Harman |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
wrote: That's a cable reel. The low rating is almost certainly to protect it when used not fully unwound. I'll bet the cable size is sufficient to blow a 13 amp fuse within the rated time in event of a short. Well if you want to split hairs between lead and cable one of which happens to be wound on a reel. Perhaps the warning about unwinding fully before use they have written is unnecessary. It tends to be ignored by many. TBH I wonder what fuse is actually fitted in the plug, enlarging the image shows the plug instruction card to show a 13 amp fuse. I reckon that is what is fitted and it relies on the inbuilt cutout it appears to have judging by the presence of the red button. That would make more sense. Relying on a punter to replace a blown 5 amp (or whatever) plug fuse with the correct one requires the optimism of a BREXIT supporter. There is this http://www.screwfix.com/p/carroll-me...mm-x-14m/2458p You didn't say it had to be below 13 amps, just non 13 amp. Are you related to Wodney? -- *A plateau is a high form of flattery* Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On Mon, 21 Nov 2016 14:23:59 +0000, wrote:
There is this http://www.screwfix.com/p/carroll-me...mm-x-14m/2458p When I wanted an extension flex (cable would be a bit awkward to handle) I was after 1.5mm. Almaost all were 1.25, so obviously 'value engineered'. I looked at the usual sources and then found that Wilko was the cheapest! Bought a reel of 50m, made up a 28m lead and still have about 18 - 20m left. Machine Mart (sorry) did have a good one but that meant going to Leicester and by the time I could do the trip the price had gone up by a fiver. -- Peter. The gods will stay away whilst religions hold sway |
Are 3A plug fuses really necessary? Why not always 13A?
On Monday, 21 November 2016 12:53:57 UTC, John Rumm wrote:
On 21/11/2016 04:09, tabbypurr wrote: On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote: On 20/11/2016 21:55, tabbypurr wrote: It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing. So grow up and stop doing it then. Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in. You said "When you have an extension lead plugged into another, or an old appliance, or something bought from China, it certainly does." ie it does matter what fuse you use. So, if you are not alluding to selecting an appropriate fuse for the extension lead, what are you suggesting? Let's get it clear in case anyone is still confused. For all plugs I pick the lowest fuse that will reliably serve. It's what I recommend others to do too. If folk don't want to, it's not my life, it's theirs. There are various situations in which it does make the difference, as well as many it doesn't. If you want to fail to provide very basic safety protection to some leads, appliances & people, again it's your life. I've already provided a list of the main situations in which it does matter. Namely old appliances noncompliant appliances extension leads A lot of these most users will never spot. They don't need to. I have no difficulty telling what fuse is going to suit. If some users do, as some do, it really ain't my issue. All I can do is recommend best practice. You and others can do whatever you/they please in life. And for the sake of clarity, I shall now state what I thought was obvious, but perhaps isn't to some. A 5A extension lead is usable for loads up to 5A continuous, and is thus best protected by a 5A fuse. You can complicate that analysis further if you want, but I don't want. NT |
Are 3A plug fuses really necessary? Why not always 13A?
In article , John
Rumm writes On 20/11/2016 02:28, wrote: On Sunday, 20 November 2016 00:11:32 UTC, John Rumm wrote: On 19/11/2016 20:13, tabbypurr wrote: On Saturday, 19 November 2016 18:56:25 UTC, John Rumm wrote: On 19/11/2016 15:34, DerbyBorn wrote: I will stick to fusing with the lowest capacity fuse to suit the current of the appliance. I want the fuse to blow as soon as possible if there is a fault. Nothing wrong with fusing appropriately, but when dealing with fault currents (in the technical sense), it makes little difference if its a 3A or 13A fuse when you try drawing 300A through it. When you have an extension lead plugged into another, or an old appliance, or something bought from China, it certainly does. You won't get a adequate fault current through too many cascaded leads, but fitting all extension leads with 3A fuses in case someone may cascade them seems a bit self defeating. Plug fuses are available in 2A 3A 5A 7A 10A & 13A rating. Fitting the correct one to leads is hardly self defeating, it prevents fires. How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? Simples. If it's a 13 amp extension lead it gets a 13A fuse. Are you proposing changing the fuse in the plug depending on what you have plugged into the far end? Don't be silly. Each plugged in appliance will have it's own appropriate fuse. The extension lead fuse simply protects the extension lead, not individual appliances/cables attached to it. Snip -- bert |
Are 3A plug fuses really necessary? Why not always 13A?
In article , "Dave Plowman (News)"
writes In article , wrote: How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? I can't imagine why you assume extension leads are all 13A rated. I assure you they're not. 10A leads get a 10A fuse, 5A leads get a 5A fuse etc. Hardly a challenge. Rather silly given the average person won't have a clue how much current things take. And if, say, a 5 amp fuse blew would likely fit a 13 amp one. Safer to make them all 13 amp. Much as has happened with all leads these days. How can a 13 amp fuse make it"SAFER" than a 5 amp one? -- bert |
Are 3A plug fuses really necessary? Why not always 13A?
On 21/11/2016 21:45, bert wrote:
In article , "Dave Plowman (News)" writes In article , wrote: How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? I can't imagine why you assume extension leads are all 13A rated. I assure you they're not. 10A leads get a 10A fuse, 5A leads get a 5A fuse etc. Hardly a challenge. Rather silly given the average person won't have a clue how much current things take. And if, say, a 5 amp fuse blew would likely fit a 13 amp one. Safer to make them all 13 amp. Much as has happened with all leads these days. How can a 13 amp fuse make it"SAFER" than a 5 amp one? Not the fuse, the flex / appliance. If you design your product so that it is adequately protected by a 13A fuse, then there is nothing the user can do to make it unsafe. If you design it so that its requires lower fusing, then it means there is a danger of it having inadequate fault protection if the user fits a 13A fuse without appreciating the implications. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
On 21/11/2016 21:19, wrote:
On Monday, 21 November 2016 12:53:57 UTC, John Rumm wrote: On 21/11/2016 04:09, tabbypurr wrote: On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote: On 20/11/2016 21:55, tabbypurr wrote: It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing. So grow up and stop doing it then. Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in. You said "When you have an extension lead plugged into another, or an old appliance, or something bought from China, it certainly does." ie it does matter what fuse you use. So, if you are not alluding to selecting an appropriate fuse for the extension lead, what are you suggesting? Let's get it clear in case anyone is still confused. For all plugs I pick the lowest fuse that will reliably serve. It's what I recommend others to do too. If folk don't want to, it's not my life, it's theirs. And how do you know what that value is? Given in many cases its not as simple as looking at the nominal run current - you may need to take into account inrush. There are various situations in which it does make the difference, as well as many it doesn't. If you want to fail to provide very basic safety protection to some leads, appliances & people, again it's your life. By basic protection do you mean fault protection? If not what else are you trying to achieve? I've already provided a list of the main situations in which it does matter. Namely old appliances noncompliant appliances extension leads A lot of these most users will never spot. They don't need to. This seems a little contradictory - first you say it matters, and now that most users don't need to spot the cases where it matters... I have no difficulty telling what fuse is going to suit. If some users do, as some do, it really ain't my issue. All I can do is recommend best practice. You and others can do whatever you/they please in life. Working out the optimal fusing is not a trivial exercise. Are you just providing fault protection or is overload protection also required? Can you achieve both with a single fuse? How do you reconcile potentially differing requirements for overload protection and breaking capacity? And for the sake of clarity, I shall now state what I thought was obvious, but perhaps isn't to some. A 5A extension lead is usable for loads up to 5A continuous, and is thus best protected by a 5A fuse. Obvious enough - you need the fuse for fault and overload protection in that case. One of the reasons why 5A leads are far less freely available than in the past. You can complicate that analysis further if you want, but I don't want. And yet you are suggesting complicating the analysis by selecting specific fuse sizes? -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
On Monday, 21 November 2016 22:13:15 UTC, John Rumm wrote:
On 21/11/2016 21:45, bert wrote: In article , "Dave Plowman (News)" writes In article , tabbypurr wrote: How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? I can't imagine why you assume extension leads are all 13A rated. I assure you they're not. 10A leads get a 10A fuse, 5A leads get a 5A fuse etc. Hardly a challenge. Rather silly given the average person won't have a clue how much current things take. And if, say, a 5 amp fuse blew would likely fit a 13 amp one. Safer to make them all 13 amp. Much as has happened with all leads these days. How can a 13 amp fuse make it"SAFER" than a 5 amp one? Not the fuse, the flex / appliance. If you design your product so that it is adequately protected by a 13A fuse, then there is nothing the user can do to make it unsafe. If you design it so that its requires lower fusing, then it means there is a danger of it having inadequate fault protection if the user fits a 13A fuse without appreciating the implications. They print the essential instructions on it and their arse is covered. NT |
Are 3A plug fuses really necessary? Why not always 13A?
On Tuesday, 22 November 2016 00:58:09 UTC, John Rumm wrote:
On 21/11/2016 21:19, tabbypurr wrote: On Monday, 21 November 2016 12:53:57 UTC, John Rumm wrote: On 21/11/2016 04:09, tabbypurr wrote: On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote: On 20/11/2016 21:55, tabbypurr wrote: It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing. So grow up and stop doing it then. Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in. You said "When you have an extension lead plugged into another, or an old appliance, or something bought from China, it certainly does." ie it does matter what fuse you use. So, if you are not alluding to selecting an appropriate fuse for the extension lead, what are you suggesting? Let's get it clear in case anyone is still confused. For all plugs I pick the lowest fuse that will reliably serve. It's what I recommend others to do too. If folk don't want to, it's not my life, it's theirs. And how do you know what that value is? Given in many cases its not as simple as looking at the nominal run current - you may need to take into account inrush. and power factor. There are various situations in which it does make the difference, as well as many it doesn't. If you want to fail to provide very basic safety protection to some leads, appliances & people, again it's your life. By basic protection do you mean fault protection? If not what else are you trying to achieve? prevention of fire & shock. A 2A fuse can prevent that in some situations where a 13A fails to. It will open when that chinese 0.1A mains lead is shorted, and when the 2 slice toaster element droops so far that suddenly it's drawing too much current and about to set fire to the bread. I've already provided a list of the main situations in which it does matter. Namely old appliances noncompliant appliances extension leads A lot of these most users will never spot. They don't need to. This seems a little contradictory - first you say it matters, and now that most users don't need to spot the cases where it matters... There's no contradiction there. I have no difficulty telling what fuse is going to suit. If some users do, as some do, it really ain't my issue. All I can do is recommend best practice. You and others can do whatever you/they please in life. Working out the optimal fusing is not a trivial exercise. Users that don't understand it can take a simplified approach, like look at the power consumption. I also remember being given cheat sheets, these applinces want 3A, the rest 13 etc. Are you just providing fault protection or is overload protection also required? Can you achieve both with a single fuse? How do you reconcile potentially differing requirements for overload protection and breaking capacity? Those questions don't need to be answered IRL. Pick the lowest fuse that does the job, that's it. Debating how well it protects what appliances in what ways doesn't achieve anything. And for the sake of clarity, I shall now state what I thought was obvious, but perhaps isn't to some. A 5A extension lead is usable for loads up to 5A continuous, and is thus best protected by a 5A fuse. Obvious enough - you need the fuse for fault and overload protection in that case. One of the reasons why 5A leads are far less freely available than in the past. You can complicate that analysis further if you want, but I don't want. And yet you are suggesting complicating the analysis by selecting specific fuse sizes? that doesn't complicate it beyond what I said at all. We all know there are users without any clue how to choose a fuse, that doesn't mean I'm going to recommend they put 13A fuses in their daisy chained 5A extension leads. Or in that Chinese electrode boiler they got on Amazon, that they are not aware of any issues with. You can if you choose, but I don't. I'm not a full time PAT tester, but have tested enough goods to know there's plenty of noncompliant, historic and faulty goods out there, and sub-13A extension leads aplenty. One can not realistically disregard the suitable fusing of such items and expect fires, shocks & deaths to not result. NT |
Are 3A plug fuses really necessary? Why not always 13A?
On 22/11/2016 02:17, wrote:
On Monday, 21 November 2016 22:13:15 UTC, John Rumm wrote: On 21/11/2016 21:45, bert wrote: In article , "Dave Plowman (News)" writes In article , tabbypurr wrote: How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? I can't imagine why you assume extension leads are all 13A rated. I assure you they're not. 10A leads get a 10A fuse, 5A leads get a 5A fuse etc. Hardly a challenge. Rather silly given the average person won't have a clue how much current things take. And if, say, a 5 amp fuse blew would likely fit a 13 amp one. Safer to make them all 13 amp. Much as has happened with all leads these days. How can a 13 amp fuse make it"SAFER" than a 5 amp one? Not the fuse, the flex / appliance. If you design your product so that it is adequately protected by a 13A fuse, then there is nothing the user can do to make it unsafe. If you design it so that its requires lower fusing, then it means there is a danger of it having inadequate fault protection if the user fits a 13A fuse without appreciating the implications. They print the essential instructions on it and their arse is covered. More typically, they ensure it only has 6' of flex such that it stays safe on a 13A fuse. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
wrote: prevention of fire & shock. A 2A fuse can prevent that in some situations where a 13A fails to. It will open when that chinese 0.1A mains lead is shorted, and when the 2 slice toaster element droops so far that suddenly it's drawing too much current and about to set fire to the bread. You'd fit a two slice toaster with a 2 amp fuse? BTW, why are you buying Chinese products with illegal mains leads? Have you reported them? -- *Why is the third hand on the watch called a second hand? Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
John Rumm wrote: They print the essential instructions on it and their arse is covered. More typically, they ensure it only has 6' of flex such that it stays safe on a 13A fuse. Think you'll find anything bought these days which conforms to EU regs will have a flex capable of blowing a 13 amp fuse in event of a short. And that's all the plug fuse is meant to do. -- *Always remember you're unique, just like everyone else. Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On Tuesday, 22 November 2016 11:11:45 UTC, Dave Plowman (News) wrote:
In article , tabbypurr wrote: prevention of fire & shock. A 2A fuse can prevent that in some situations where a 13A fails to. It will open when that chinese 0.1A mains lead is shorted, and when the 2 slice toaster element droops so far that suddenly it's drawing too much current and about to set fire to the bread. You'd fit a two slice toaster with a 2 amp fuse? No BTW, why are you buying Chinese products with illegal mains leads? I'm not. Any more silly qestions? Have you reported them? huh? NT |
Are 3A plug fuses really necessary? Why not always 13A?
John Rumm wrote:
On 21/11/2016 21:19, wrote: On Monday, 21 November 2016 12:53:57 UTC, John Rumm wrote: On 21/11/2016 04:09, tabbypurr wrote: On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote: On 20/11/2016 21:55, tabbypurr wrote: It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing. So grow up and stop doing it then. Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in. You said "When you have an extension lead plugged into another, or an old appliance, or something bought from China, it certainly does." ie it does matter what fuse you use. So, if you are not alluding to selecting an appropriate fuse for the extension lead, what are you suggesting? Let's get it clear in case anyone is still confused. For all plugs I pick the lowest fuse that will reliably serve. It's what I recommend others to do too. If folk don't want to, it's not my life, it's theirs. And how do you know what that value is? Given in many cases its not as simple as looking at the nominal run current - you may need to take into account inrush. There are various situations in which it does make the difference, as well as many it doesn't. If you want to fail to provide very basic safety protection to some leads, appliances & people, again it's your life. By basic protection do you mean fault protection? If not what else are you trying to achieve? I've already provided a list of the main situations in which it does matter. Namely old appliances noncompliant appliances extension leads A lot of these most users will never spot. They don't need to. This seems a little contradictory - first you say it matters, and now that most users don't need to spot the cases where it matters... I have no difficulty telling what fuse is going to suit. If some users do, as some do, it really ain't my issue. All I can do is recommend best practice. You and others can do whatever you/they please in life. Working out the optimal fusing is not a trivial exercise. Are you just providing fault protection or is overload protection also required? Can you achieve both with a single fuse? How do you reconcile potentially differing requirements for overload protection and breaking capacity? And for the sake of clarity, I shall now state what I thought was obvious, but perhaps isn't to some. A 5A extension lead is usable for loads up to 5A continuous, and is thus best protected by a 5A fuse. Obvious enough - you need the fuse for fault and overload protection in that case. One of the reasons why 5A leads are far less freely available than in the past. The fact the fuse can't provide overload protection in the common circumstance of the lead being used without being unreeled is probably why they often have heat operated overload cutouts in the reel. Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? You can complicate that analysis further if you want, but I don't want. And yet you are suggesting complicating the analysis by selecting specific fuse sizes? -- Roger Hayter |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
wrote: On Tuesday, 22 November 2016 11:11:45 UTC, Dave Plowman (News) wrote: In article , tabbypurr wrote: prevention of fire & shock. A 2A fuse can prevent that in some situations where a 13A fails to. It will open when that chinese 0.1A mains lead is shorted, and when the 2 slice toaster element droops so far that suddenly it's drawing too much current and about to set fire to the bread. You'd fit a two slice toaster with a 2 amp fuse? No So why did you mention it? BTW, why are you buying Chinese products with illegal mains leads? I'm not. Any more silly qestions? Have you reported them? huh? So why did you mention it? NT -- *It's o.k. to laugh during sexŒ.Œ.just don't point! Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On Tuesday, 22 November 2016 02:35:44 UTC, tabbyp wrote:
On Tuesday, 22 November 2016 00:58:09 UTC, John Rumm wrote: On 21/11/2016 21:19, tabbypurr wrote: On Monday, 21 November 2016 12:53:57 UTC, John Rumm wrote: On 21/11/2016 04:09, tabbypurr wrote: On Sunday, 20 November 2016 22:46:03 UTC, John Rumm wrote: There are various situations in which it does make the difference, as well as many it doesn't. If you want to fail to provide very basic safety protection to some leads, appliances & people, again it's your life. By basic protection do you mean fault protection? If not what else are you trying to achieve? prevention of fire & shock. A 2A fuse can prevent that in some situations where a 13A fails to. It will open when that chinese 0.1A mains lead is shorted, and when the 2 slice toaster element droops so far that suddenly it's drawing too much current and about to set fire to the bread. Are you just providing fault protection or is overload protection also required? Can you achieve both with a single fuse? How do you reconcile potentially differing requirements for overload protection and breaking capacity? Those questions don't need to be answered IRL. Pick the lowest fuse that does the job, that's it. Debating how well it protects what appliances in what ways doesn't achieve anything. What the fuse achieves varies in each case. Sometimes it provides needed fault protection, more often not. Sometimes it provides overload protection, more often not. But it need not be analysed case by case, just put the right fuse in and you get whatever the best protection is a plug fuse can provide each time. NT |
Are 3A plug fuses really necessary? Why not always 13A?
On 22/11/2016 12:06, Roger Hayter wrote:
John Rumm wrote: On 21/11/2016 21:19, wrote: And for the sake of clarity, I shall now state what I thought was obvious, but perhaps isn't to some. A 5A extension lead is usable for loads up to 5A continuous, and is thus best protected by a 5A fuse. Obvious enough - you need the fuse for fault and overload protection in that case. One of the reasons why 5A leads are far less freely available than in the past. The fact the fuse can't provide overload protection in the common circumstance of the lead being used without being unreeled is probably why they often have heat operated overload cutouts in the reel. For extension leads on a reel, yes. There is a second class of lead which are the multiway sockets on a (typically shorter) lead. There the 13A fuse also has to provide overload protection since its possible for the user to abuse them. (and this is also a cases where I would have some sympathy with fittings say a 10A fuse to some of the cheaper examples of those since tests have shown a number to not really be capable of sustained 13A load). Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? Indeed it is. I was just trying to get the bottom of what Nige was actually attempting to achieve with his lowest possible fuse that's adequate scenario - I understand the adequate bit - it must offer fault protection, but assuming we have got past the "it gives adequate fault protection" stage, there seem to be diminishing returns. Depending on the appliance, it could end up being an exercise in blowing lots of small fuses working your way up to the optimal one. Most appliances are not going to need specific overload protection and many that do may include a 750mA (or whatever) 20mm glass cartridge fuse for the purpose. Those alone though won't provide fault protection (inadequate breaking capacity usually), so sny BS1362 fuse in the plug will do in many of those cases. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
On Tuesday, 22 November 2016 20:23:21 UTC, John Rumm wrote:
On 22/11/2016 12:06, Roger Hayter wrote: Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? Indeed it is. I was just trying to get the bottom of what Nige was actually attempting to achieve with his lowest possible fuse that's adequate scenario - I understand the adequate bit - it must offer fault protection, but assuming we have got past the "it gives adequate fault protection" stage, there seem to be diminishing returns. Depending on the appliance, it could end up being an exercise in blowing lots of small fuses working your way up to the optimal one. Most appliances are not going to need specific overload protection and many that do may include a 750mA (or whatever) 20mm glass cartridge fuse for the purpose. Those alone though won't provide fault protection (inadequate breaking capacity usually), so sny BS1362 fuse in the plug will do in many of those cases. But a small significant percentage of appliances have neither short nor overload protection on a 13A fuse. Why you don't get that I really don't get. NT |
Are 3A plug fuses really necessary? Why not always 13A?
On 22/11/2016 22:47, wrote:
On Tuesday, 22 November 2016 20:23:21 UTC, John Rumm wrote: On 22/11/2016 12:06, Roger Hayter wrote: Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? Indeed it is. I was just trying to get the bottom of what Nige was actually attempting to achieve with his lowest possible fuse that's adequate scenario - I understand the adequate bit - it must offer fault protection, but assuming we have got past the "it gives adequate fault protection" stage, there seem to be diminishing returns. Depending on the appliance, it could end up being an exercise in blowing lots of small fuses working your way up to the optimal one. Most appliances are not going to need specific overload protection and many that do may include a 750mA (or whatever) 20mm glass cartridge fuse for the purpose. Those alone though won't provide fault protection (inadequate breaking capacity usually), so sny BS1362 fuse in the plug will do in many of those cases. But a small significant percentage of appliances have neither short nor overload protection on a 13A fuse. Why you don't get that I really don't get. I "get" that crusty old crap, and 5A extension leads need specific fusing. I also get that if one understands these things there is no harm in selecting a lower rated fuse. However we live in a world where appliance designers accept that many users won't be able to make a judgement call on this, and hence designing them to remain safe on a 13A fuse is the only prudent option. I also get that any electrical goods for sale now will have to be CE marked, and hence suitable for sale anywhere in the EU. How do you think that these devices which you believe are "neither short nor overload protection on a 13A fuse", are going to fare in countries other than the UK, where 16A circuit breakers are commonly the only fault or overload protection between CU and appliance? Lets do a sum... Lets assume we have a circuit with a B32 MCB and its at its maximum length permitted by the 1.44 Ohms Zs. Lets now take 1.8m of skimpy 0.5mm^2 flex and add on its ~156 mOhm, giving a total of ~ 1.6 Ohms. So we get a PFC of 230/1.6 = 162A which is just enough to open the MCB on the magnetic part of its response. So lets check the conductor size required: s = sqrt( 162^2 x 0.1 ) / 115 = 0.44mm^2 So even then, the flex lives to fight another day. So if I were going to boil this down to advice for non technical users, I would say leave whatever fuse it came with in it. If you need to replace it, use the same one. In general this is not something to worry about. If you are skilled, and have a particular scenario in mind where you know that you will be running a small flex appliance outside of its design parameters (like running it on the end of 100m of extension cable plugged into an already long circuit), by all means fuse down. For normal every day stuff (aka the general case), you are more likely to hurt yourself tripping over the lead. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, 23 November 2016 00:01:55 UTC, John Rumm wrote:
On 22/11/2016 22:47, tabbypurr wrote: On Tuesday, 22 November 2016 20:23:21 UTC, John Rumm wrote: On 22/11/2016 12:06, Roger Hayter wrote: Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? Indeed it is. I was just trying to get the bottom of what Nige was actually attempting to achieve with his lowest possible fuse that's adequate scenario - I understand the adequate bit - it must offer fault protection, but assuming we have got past the "it gives adequate fault protection" stage, there seem to be diminishing returns. Depending on the appliance, it could end up being an exercise in blowing lots of small fuses working your way up to the optimal one. Most appliances are not going to need specific overload protection and many that do may include a 750mA (or whatever) 20mm glass cartridge fuse for the purpose. Those alone though won't provide fault protection (inadequate breaking capacity usually), so sny BS1362 fuse in the plug will do in many of those cases. But a small significant percentage of appliances have neither short nor overload protection on a 13A fuse. Why you don't get that I really don't get. I "get" that crusty old crap, and 5A extension leads need specific fusing.. and new crap that is often CE mismarked. I also get that if one understands these things there is no harm in selecting a lower rated fuse. However we live in a world where appliance designers accept that many users won't be able to make a judgement call on this, and hence designing them to remain safe on a 13A fuse is the only prudent option. I also get that any electrical goods for sale now will have to be CE marked, and hence suitable for sale anywhere in the EU. Some are mismarked, sometimes they don't bother CE marking them. CE marking doesn't mean too much in practice. How do you think that these devices which you believe are "neither short nor overload protection on a 13A fuse", are going to fare in countries other than the UK, where 16A circuit breakers are commonly the only fault or overload protection between CU and appliance? obviously they are neither short nor overload protected, and cause fires, shocks and death. What about that is not completely obvious? Lets do a sum... Lets assume we have a circuit with a B32 MCB and its at its maximum length permitted by the 1.44 Ohms Zs. Lets now take 1.8m of skimpy 0.5mm^2 flex and add on its ~156 mOhm, giving a total of ~ 1.6 Ohms. So we get a PFC of 230/1.6 = 162A which is just enough to open the MCB on the magnetic part of its response. So lets check the conductor size required: s = sqrt( 162^2 x 0.1 ) / 115 = 0.44mm^2 So even then, the flex lives to fight another day. So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. So if I were going to boil this down to advice for non technical users, I would say leave whatever fuse it came with in it. If you need to replace it, use the same one. In general this is not something to worry about. So you don't recommend goods be protected against short and overload. OK, but there's no point defending that. If you are skilled, and have a particular scenario in mind where you know that you will be running a small flex appliance outside of its design parameters (like running it on the end of 100m of extension cable plugged into an already long circuit), by all means fuse down. For normal every day stuff (aka the general case), you are more likely to hurt yourself tripping over the lead. But if you compare death rate, failure to fuse properly is the bigger risk. If you don't see an issue with people having at risk appliances, what is there left to say. You seem to live in a naive world where every appliance is new and compliant. Real life is just not like that. NT |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. -- *Starfishes have no brains * Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On Wednesday, 23 November 2016 11:07:00 UTC, Dave Plowman (News) wrote:
In article , wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? Lots of people buy cheap **** in the hope it will do a simialar thing to a full priced version of the same thing. Some just because it looks the same and others might think they own a better product than they actually do, or it's an image thing where they fool themselves too. if people didn't want such things we wouldn't be getting fake things coming into the UK or anywhere else. If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. It can also cost more to adhere to any regualtions that are imposed by an authority. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. I handed out a 'classic' 3.15 AS 20mm fuse 2 weeks ago a long time since I've handed one of them out. |
Are 3A plug fuses really necessary? Why not always 13A?
On 23/11/2016 08:30, wrote:
On Wednesday, 23 November 2016 00:01:55 UTC, John Rumm wrote: On 22/11/2016 22:47, tabbypurr wrote: On Tuesday, 22 November 2016 20:23:21 UTC, John Rumm wrote: On 22/11/2016 12:06, Roger Hayter wrote: Realistically the fuse is not going to provide overload protection, just fault protection for the flex for modern small electronic appliances. I thought that was what you said earlier in the thread? Indeed it is. I was just trying to get the bottom of what Nige was actually attempting to achieve with his lowest possible fuse that's adequate scenario - I understand the adequate bit - it must offer fault protection, but assuming we have got past the "it gives adequate fault protection" stage, there seem to be diminishing returns. Depending on the appliance, it could end up being an exercise in blowing lots of small fuses working your way up to the optimal one. Most appliances are not going to need specific overload protection and many that do may include a 750mA (or whatever) 20mm glass cartridge fuse for the purpose. Those alone though won't provide fault protection (inadequate breaking capacity usually), so sny BS1362 fuse in the plug will do in many of those cases. But a small significant percentage of appliances have neither short nor overload protection on a 13A fuse. Why you don't get that I really don't get. I "get" that crusty old crap, and 5A extension leads need specific fusing. and new crap that is often CE mismarked. I am not sure what your fascination with dangerous and substandard goods is in particular. Yes there is loads of crap that is electrically unsafe and being sold illegally. Don't lul yourself into a false sense of security that sticking a 3A fuse in it its going to suddenly make it safe - it will likely still be dangerous! The lack of fusing or inadequate mains cable is usually the tip of the iceberg. Look closely and you will often see metalwork coupled directly to mains, inadequate isolation between mains and LV side of circuits. Low quality components (like transformers with inadequate insulation between primary and secondary windings), lack of thermal protection, unsafe plastics and smoke / fume hazards and so on. e.g. one of many: https://www.youtube.com/watch?v=QwqFkelUs_g I you want to keep safe from cheap crap goods, then don't buy them in the first place. I also get that if one understands these things there is no harm in selecting a lower rated fuse. However we live in a world where appliance designers accept that many users won't be able to make a judgement call on this, and hence designing them to remain safe on a 13A fuse is the only prudent option. I also get that any electrical goods for sale now will have to be CE marked, and hence suitable for sale anywhere in the EU. Some are mismarked, sometimes they don't bother CE marking them. CE marking doesn't mean too much in practice. How do you think that these devices which you believe are "neither short nor overload protection on a 13A fuse", are going to fare in countries other than the UK, where 16A circuit breakers are commonly the only fault or overload protection between CU and appliance? obviously they are neither short nor overload protected, and cause fires, shocks and death. What about that is not completely obvious? So your advice to someone using one of these appliances in Germany for example would be? Lets do a sum... Lets assume we have a circuit with a B32 MCB and its at its maximum length permitted by the 1.44 Ohms Zs. Lets now take 1.8m of skimpy 0.5mm^2 flex and add on its ~156 mOhm, giving a total of ~ 1.6 Ohms. So we get a PFC of 230/1.6 = 162A which is just enough to open the MCB on the magnetic part of its response. So lets check the conductor size required: s = sqrt( 162^2 x 0.1 ) / 115 = 0.44mm^2 So even then, the flex lives to fight another day. So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. They are unsafe when connected to the mains. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. See above: 'I "get" that crusty old crap, and 5A extension leads need specific fusing.' (although to be fair to 60's hifi, much of it was a better quality construction than some of the modern crap). So if I were going to boil this down to advice for non technical users, I would say leave whatever fuse it came with in it. If you need to replace it, use the same one. In general this is not something to worry about. So you don't recommend goods be protected against short and overload. You are mistaken. OK, but there's no point defending that. To paraphrase that nice Mr Pauli, you are not even wrong. If you are skilled, and have a particular scenario in mind where you know that you will be running a small flex appliance outside of its design parameters (like running it on the end of 100m of extension cable plugged into an already long circuit), by all means fuse down. For normal every day stuff (aka the general case), you are more likely to hurt yourself tripping over the lead. But if you compare death rate, Link to stats demonstrating an increased death rate from using the supplied fuse please. failure to fuse properly is the bigger risk. If you don't see an issue with people having at risk appliances, what is there left to say. You seem to be engaging in an exercise in reductio ad absurdum. You seem to live in a naive world where every appliance is new and compliant. Real life is just not like that. Now, allowing for the caveats that we have already highlighted like thin extension leads and old kit etc (remember we are talking in general here, the majority of cases, not absolute black or white; hell I want an *argument* with someone on the internet!) I am struggling to think of any of the hundreds of electrical appliances around me where this is an issue... I can't bring to mind many. An oldish set of Christmas lights perhaps? I don't recall buying anything with a mains lead of less than 0.5mm^2 in decades. I have had equipment supplied with non conforming plugs on (inadequate overhang round pins, no internal fuse) - they *may* also have had thin wire as well, I don't know I did not look, but I don't really think the bin cared much though. I do have on odd one here though. A new Cambridge Audio HiFi amp. The English section of the user guide makes a big point about including a section for the "UK only" and includes instructions on fitting a plug with the requirement that it must contain a 3A fuse, and if you remove the plug then to provide fusing elsewhere. Its a curious section since if you look at the lead its of adequate cross section to be protected on a 13A fuse (or for that matter a 16A MCB), and a quick glance though the ventilation slots shows internal overload fusing with a 2A time delayed 20mm fuse, and warnings silk screened around it to replace only with a like fuse. The multilingual manual has blank sections in the same place in all the other languages. Not sure if it was an exercise in "because we could", or just tin knickers. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
Dave Plowman (News) wrote:
In article , wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. Interestingly, I just had a counter-example where a 3A fuse might have prevented equipment damage due to a fault. A Grundfos pump (mention the name because it is the second one to do the same) failed short-circuit and melted a trace on the controller PCB, without actually blowing the 13A plug fuse or tripping the MCB. A 3A fuse might have prevented this. However, I haven't checked whether the oil pump inrush current is too high for a 3A fuse yet. -- Roger Hayter |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
whisky-dave wrote: On Wednesday, 23 November 2016 11:07:00 UTC, Dave Plowman (News) wrote: In article , wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? Lots of people buy cheap **** in the hope it will do a simialar thing to a full priced version of the same thing. Some just because it looks the same and others might think they own a better product than they actually do, or it's an image thing where they fool themselves too. if people didn't want such things we wouldn't be getting fake things coming into the UK or anywhere else. There's a very big difference between a fake and something merely sold as cheaply as possible. The former is an attempt to deceive. So everything else goes out the window. The latter to capture a sector of the market. A low cost product may or may not be value for money. The obvious one being power tools. A Lidl cordless drill at 40 quid almost certainly isn't as good as a 100 quid Makita. But may perform DIY tasks more than adequately. If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. It can also cost more to adhere to any regualtions that are imposed by an authority. Anything on sale in the UK should conform to UK regs. No point in having them if not enforced. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. I handed out a 'classic' 3.15 AS 20mm fuse 2 weeks ago a long time since I've handed one of them out. I've got a nice big selection box of 20mm fuses. Hope they don't have a shelf life. ;-) -- *Failure is not an option. It's bundled with your software. Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
In article ,
Roger Hayter wrote: Interestingly, I just had a counter-example where a 3A fuse might have prevented equipment damage due to a fault. A Grundfos pump (mention the name because it is the second one to do the same) failed short-circuit and melted a trace on the controller PCB, without actually blowing the 13A plug fuse or tripping the MCB. A 3A fuse might have prevented this. However, I haven't checked whether the oil pump inrush current is too high for a 3A fuse yet. Did that pump come with a fitted 13 amp plug? Must admit to never having seen one that did. A well engineered heating system would include specific fuses for each of the outboard components. Although I do realise few will. My Viessmann boiler has individual fuse protection for everything outside of the main PCB. Using through hole PCB mount fuses. Which are not listed as being replaceable. Working this out saved me the cost of a new PCB when the gas valve failed due to getting soaked in water, and took that fuse. -- *Pride is what we have. Vanity is what others have. Dave Plowman London SW To e-mail, change noise into sound. |
Are 3A plug fuses really necessary? Why not always 13A?
On 23/11/2016 13:23, Roger Hayter wrote:
Dave Plowman (News) wrote: In article , wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. Interestingly, I just had a counter-example where a 3A fuse might have prevented equipment damage due to a fault. A Grundfos pump (mention the name because it is the second one to do the same) failed short-circuit and melted a trace on the controller PCB, without actually blowing the 13A plug fuse or tripping the MCB. Except that is not a counter example - since pumps are not domestic appliances supplied with pre-fitted lead and plug. They intended to be installed as a component of a larger system by competent people who would understand the system fusing requirements. A 3A fuse might have prevented this. However, I haven't checked whether the oil pump inrush current is too high for a 3A fuse yet. The circulator on its own would probably be OK on 3A (its an induction motor and has quite high inrush - but its a small motor), however 5A would likely be more appropriate for the whole CH system. Alas PCB traces are quite often the unintentional weak spot in many systems. I had a cooker hood the blew a couple of traces on its main switching PCB when one of its 40W incandescent lamps failed short at switch on. It was 3A fused and the fuse was fine! -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
Are 3A plug fuses really necessary? Why not always 13A?
In article , John
Rumm writes On 21/11/2016 21:45, bert wrote: In article , "Dave Plowman (News)" writes In article , wrote: How do you chose the "correct" fuse for an extension lead (assuming the lead is designed for a 13A load)? I can't imagine why you assume extension leads are all 13A rated. I assure you they're not. 10A leads get a 10A fuse, 5A leads get a 5A fuse etc. Hardly a challenge. Rather silly given the average person won't have a clue how much current things take. And if, say, a 5 amp fuse blew would likely fit a 13 amp one. Safer to make them all 13 amp. Much as has happened with all leads these days. How can a 13 amp fuse make it"SAFER" than a 5 amp one? Not the fuse, the flex / appliance. If you design your product so that it is adequately protected by a 13A fuse, then there is nothing the user can do to make it unsafe. If you design it so that its requires lower fusing, then it means there is a danger of it having inadequate fault protection if the user fits a 13A fuse without appreciating the implications. I don't think anyone has suggested that anyone should now design an appliance to depend on the presence of a plug fuse less than 13 amp for safety. However I do not think that for devices that only require small currents (including all your surges etc.) there is any harm done in fitting a lower value fuse. Whether anything might be achieved by that depends on the specifics of the attached appliance in terms of its on board safety features, quality of materials and manufacturing standard and adherence to current regulations. -- bert |
Are 3A plug fuses really necessary? Why not always 13A?
John Rumm wrote:
On 23/11/2016 13:23, Roger Hayter wrote: Dave Plowman (News) wrote: In article , wrote: So those chinese goods with barely 0.1mm2 are uprotected on a 13A fuse. I ask again. Why are you buying such things that you know to be rubbish? If you're not, no point in telling the world they should fit an appropriate fuse, as they're not listening. And wouldn't understand anyway. And that 1960s hifi with 0.1mm dia mains wiring inside ditto. Must have been real rubbish if it didn't have an equipment fuse. Interestingly, I just had a counter-example where a 3A fuse might have prevented equipment damage due to a fault. A Grundfos pump (mention the name because it is the second one to do the same) failed short-circuit and melted a trace on the controller PCB, without actually blowing the 13A plug fuse or tripping the MCB. Except that is not a counter example - since pumps are not domestic appliances supplied with pre-fitted lead and plug. They intended to be installed as a component of a larger system by competent people who would understand the system fusing requirements. Yes I am expressing myself badly, aren't I? I am talking about an oii-fired combi boiler which contains two circulating pumps. It has no internal fuses at all. It is controlled from a standard CH controller which has no fuses on inputs or outputs and is connected to the mains by a standard three pin plug. This choice is no doubt affected by the adjacent placement of a socket the previous owner intended to run from a generator.[1] I am not sure I am willing to stock more than two kinds of plug fuse, and 13A and 3A seem to be the preferred ones. A 3A fuse might have prevented this. However, I haven't checked whether the oil pump inrush current is too high for a 3A fuse yet. The circulator on its own would probably be OK on 3A (its an induction motor and has quite high inrush - but its a small motor), however 5A would likely be more appropriate for the whole CH system. I was thinking of the oil pump and fan, which have a common motor with a significant torque but I have no details except that it has a starting capacitor and no obvious brushes so I suppose it is some kind of induction motor. Alas PCB traces are quite often the unintentional weak spot in many systems. I had a cooker hood the blew a couple of traces on its main switching PCB when one of its 40W incandescent lamps failed short at switch on. It was 3A fused and the fuse was fine! [1] The socket is to be connected to a generator which is intended to be earthed to a rather weedy earth stake outside. In conjunction with the house PME system this is a whole other can of worms. -- Roger Hayter |
Are 3A plug fuses really necessary? Why not always 13A?
Frank Erskine wrote:
I don't know whether or not "intermediate" BS1362 fuses such as 5A or 7A are still available. I've just given a packet of 5A fuses to my neighbour, they definitely exist. In my toolbox I have packets of 3A, 5A and 13A. jgh |
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