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Small problem about a plug fuse

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24

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  • GDB2222
    GDB2222 Posts: 26,190 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    I suggest  that LL should buy a 5 amp fuse, and ask someone to fit it. It’s a tiny job, and she will be very, very slightly safer, plus considerably happier!

    In the meantime, she doesn’t need to panic, as the risk with the 13 amp fuse is truly tiny. 
    No reliance should be placed on the above! Absolutely none, do you hear?
  • Section62
    Section62 Posts: 9,710 Forumite
    1,000 Posts Fourth Anniversary Name Dropper
     
    But, until you find out for sure, please don't worry about it. LOTS of appliances in your kitchen will have 13A fuses in them, and you don't give these a second thought. You would have to be staggeringly unlucky for a fault to develop that blows a 5A fuse but not a 13A one. So, find out for sure (put the make and model on here, for example), but meanwhile don't worry.

    If that were true the committee responsible for drafting BS1362 could have just specified 13A fuses and knocked off early for lunch.

    People who replace a blown 5A (or 3A) fuse with a 13A one are playing Russian roulette, unless of course 13A is the correct rating for the appliance.

    Given the final rupture currents for BS1362 fuses are usually much higher than the fuse rating, the difference between the current which causes a 5A fuse to blow, and the current a 13A fuse can pass for a surprisingly long length of time, means a significant difference in protection level.  I.e. lots of scope for a fault which will blow a 5A fuse very quickly, but leave a 13A fuse passing current for potentially dangerously long lengths of time.

    My preference if a fault develops, particularly if my body is part of that fault situation, would be for the fuse to blow in a very small fraction of a second.  Hence the need to use the lowest rated fuse appropriate for the normal load.

    LilacLillie doesn't need to panic.  But equally it would be wrong to go away with the idea that 'lucky' people don't need to worry about using the correct fuse.
  • Section62 said:

    People who replace a blown 5A (or 3A) fuse with a 13A one are playing Russian roulette, unless of course 13A is the correct rating for the appliance.

    ..

    My preference if a fault develops, particularly if my body is part of that fault situation, would be for the fuse to blow in a very small fraction of a second.  Hence the need to use the lowest rated fuse appropriate for the normal load.

    LilacLillie doesn't need to panic.  But equally it would be wrong to go away with the idea that 'lucky' people don't need to worry about using the correct fuse.
    I'm sorry, that is scaremongering. "Russian Roulette"? As others have said, if there is a fault, it will just as easily blow a 13A as a 5A. It's microscopically unlikely that there will be a fault that causes the freezer to draw say 10-12 amps thus a danger caused by not having a 5A fuse fitted.

    And if you think the time to blow difference between a 13A and 5A wired fuse will offer you any kind of protection against death from electric shock, then you're wrong.

    "It's the volts that jolts but the mils that kills" is what I learned as a young engineer (mils being milliamps). A typical RCB/RCD is designed to trip at 30 milliamps almost 200 times lower than the current that a 5A is likely to blow at.

    https://www.elcosh.org/document/1624/888/d000543/section2.html

    Signature on holiday for two weeks
  • Section62
    Section62 Posts: 9,710 Forumite
    1,000 Posts Fourth Anniversary Name Dropper
    Section62 said:

    People who replace a blown 5A (or 3A) fuse with a 13A one are playing Russian roulette, unless of course 13A is the correct rating for the appliance.

    ..

    My preference if a fault develops, particularly if my body is part of that fault situation, would be for the fuse to blow in a very small fraction of a second.  Hence the need to use the lowest rated fuse appropriate for the normal load.

    LilacLillie doesn't need to panic.  But equally it would be wrong to go away with the idea that 'lucky' people don't need to worry about using the correct fuse.
    I'm sorry, that is scaremongering. "Russian Roulette"? As others have said, if there is a fault, it will just as easily blow a 13A as a 5A. It's microscopically unlikely that there will be a fault that causes the freezer to draw say 10-12 amps thus a danger caused by not having a 5A fuse fitted.
    My comment wasn't limited to freezers, but I stand by what I said.  The reason why BS1362 fuses are available in different ratings is to allow the lowest rated fuse (compatible with the appliance load) to be used which affords greater protection in terms of time taken to denergise the circuit and/or allows smaller conductor/component sizes to be used whilst not increasing risk of damage/fire.

    And if you think the time to blow difference between a 13A and 5A wired fuse will offer you any kind of protection against death from electric shock, then you're wrong. "It's the volts that jolts but the mils that kills" is what I learned as a young engineer (mils being milliamps). A typical RCB/RCD is designed to trip at 30 milliamps almost 200 times lower than the current that a 5A is likely to blow at.

    https://www.elcosh.org/document/1624/888/d000543/section2.html

    Unfortunately it is you who has got this wrong.  The slogan you learned as a young engineer is only half the story.

    Firstly, the length of time a given current flows through the body for is also a factor in the risk of injury/death.  Hence the aim in electrical protection design to stop the flow of current as quickly as possible, compatible with not interferring with normal use (as well as minimising energy/damage involved in faults which don't affect living things).  Hence RCDs being specified in terms of maximum disconnection times as well as trip current.  It is current and time which does damage to human flesh.

    From your own link - "The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes through the body." and "Longer exposure times increase the danger to the shock victim. For example, a current of 100 mA applied for 3 seconds is as dangerous as a current of 900 mA applied for a fraction of a second (0.03 seconds)."

    Your comment also makes the potentially dangerous assumption that all appliances are connected to circuits protected by RCDs.  Nobody thought to ask the OP whether the freezer was plugged in to an RCD protected circuit before declaring a 13A fuse would be OK. Plenty of people still have old-style fused CUs with no RCD protection.

    Secondly, your comment is also mistaken in thinking that an RCD protects in all circumstances - they don't.  The 30mA rating of an RCD is the differential between the current in the 'live' conductor and that in the neutral - in other words the current 'leaking' to earth via a person or other object. If the whole current is flowing through the fault/person and returning via the neutral conductor then the RCD won't 'see' anything wrong and therefore won't trip.  In that situation your health/life depends on either the fuse in the plug/FSU blowing, or else the MCB/fuse in the consumer unit tripping/blowing.

    Which is where 'my preference' in my previous post comes from.  Whilst it is no guarantee of survival, in circumstances where an RCD is absent/failed/ineffective I would - if in any way conscious of the situation - much prefer to know I've only got to wait for a 3/5A fuse to blow, rather than a 13A one or the 30/32A whole circuit protection device. YMMV here.

    It is fundamentally bad/dangerous advice to suggest that a higher-rated fuse can be substituted for a lower rated one without risk.  This is not "scaremongering" - it is basic electrical safety.
  • Bendy_House
    Bendy_House Posts: 4,756 Forumite
    1,000 Posts Second Anniversary Name Dropper
    edited 28 September 2022 at 3:09PM
    Section62 said:
     
    But, until you find out for sure, please don't worry about it. LOTS of appliances in your kitchen will have 13A fuses in them, and you don't give these a second thought. You would have to be staggeringly unlucky for a fault to develop that blows a 5A fuse but not a 13A one. So, find out for sure (put the make and model on here, for example), but meanwhile don't worry.


    I thought I should repost my offering, as you seem to have highlighted the only part that doesn't bear highlighting.
    Hi LL. Have you Googled the actual make and model that you have, so the spec can be checked?
    If you cannot find the specific info on t'net, then drop the manufacturer an email and ask them what size of fuse it should have.
    Yes, if it has always run on a 5A fuse, then clearly it was able to cope, and the lower the fuse rating, the slightly more protection your appliance has.
    But, until you find out for sure, please don't worry about it. LOTS of appliances in your kitchen will have 13A fuses in them, and you don't give these a second thought. You would have to be staggeringly unlucky for a fault to develop that blows a 5A fuse but not a 13A one. So, find out for sure (put the make and model on here, for example), but meanwhile don't worry.
    Russian Roulette tends to have a one-in-six chance of things going awry, like one's brain. A leccy fault that that isn't protected because of the additional 8A range of a temporarily-replaced fuse has somewhat better odds. Staggeringly better.

    Sheeesh :-)
     
  • Section62
    Section62 Posts: 9,710 Forumite
    1,000 Posts Fourth Anniversary Name Dropper

    Russian Roulette tends to have a one-in-six chance of things going awry, like one's brain. A leccy fault that that isn't protected because of the additional 8A range of a temporarily-replaced fuse has somewhat better odds. Staggeringly better.

    Sheeesh :-)
     
    Care to show your calculation of those odds?

    It isn't an "additional 8A range".  The characteristics of BS1362 fuses are non-linear. E.g. a 13A fuse will pass 20A indefinitely, approx 50A for 1 second, or 100A for up to around a third of a second.

    The rating (e.g. 13A) relates to the maximum current the fuse can pass without overheating the plug. You can't simply deduct one of the lower fuse rating values from one of the higher ones and come up with 8A as some kind of assessment of safety margin or odds that swapping fuses would give you. It just doesn't work that way.
  • Bendy_House
    Bendy_House Posts: 4,756 Forumite
    1,000 Posts Second Anniversary Name Dropper
    edited 28 September 2022 at 4:18PM
    Section62 said:

    Russian Roulette tends to have a one-in-six chance of things going awry, like one's brain. A leccy fault that that isn't protected because of the additional 8A range of a temporarily-replaced fuse has somewhat better odds. Staggeringly better.

    Sheeesh :-)
     
    Care to show your calculation of those odds?

    It isn't an "additional 8A range".  The characteristics of BS1362 fuses are non-linear. E.g. a 13A fuse will pass 20A indefinitely, approx 50A for 1 second, or 100A for up to around a third of a second.

    The rating (e.g. 13A) relates to the maximum current the fuse can pass without overheating the plug. You can't simply deduct one of the lower fuse rating values from one of the higher ones and come up with 8A as some kind of assessment of safety margin or odds that swapping fuses would give you. It just doesn't work that way.
    By your own example, you clearly can.

    How much will  5A fuse carry indefinitely?

    So a plug can draw 20A 'indefinitely' via a 13A fuse, but 13A is the max it can carry without overheating the plug? What happens between 13 and 20? A very very hot plug?

    I'm confused.

    Anyhoo, RR's odds begin at 6to1. The chances of a leccy fault leading to a disaster just 'cos a 5A jobbie was temporarily swapped for a 13A one, is precisely very high. Indeed.
    Very.
    Enough to not lose sleep over.
  • Section62
    Section62 Posts: 9,710 Forumite
    1,000 Posts Fourth Anniversary Name Dropper

    I'm confused.

    Yes.  Which is why I was suggesting your calculation/estimation of odds isn't really a sound basis for giving advice on the safety of substituting a 13A fuse for a 5A one.

    Ideally that call should be left to the manufacturer of the appliance, who would have employed electrical engineers to work out what the correct fuse rating should be to give the required level of protection.
  • Ectophile
    Ectophile Posts: 7,970 Forumite
    Part of the Furniture 1,000 Posts Photogenic Name Dropper
    There are only two standard sizes of fuse for a UK plug - 3A and 13A.  Appliance manufacturers should not assume that consumers keep any other size of fuse handy.  5A is common, but still non-standard.

    The fuse is to protect the flex, not the appliance.  If the appliance needs a fuse, it should have one of its own.

    The appliances sold in the UK are the same ones as in Europe, where they don't even have fuses in plugs.  So manufacturers shouldn't assume that there is even a fuse in the plug at all.  They are still designed to be safe when fitted with a French or German 15A plug.
    If it sticks, force it.
    If it breaks, well it wasn't working right anyway.
  • Section62 said:
    Yes.  Which is why I was suggesting your calculation/estimation of odds isn't really a sound basis for giving advice on the safety of substituting a 13A fuse for a 5A one.

    Ideally that call should be left to the manufacturer of the appliance, who would have employed electrical engineers to work out what the correct fuse rating should be to give the required level of protection.
    And, after they have crunched the numbers to exhaustion, it's, "Well, folks, 3A or 13A, eh?"

    I mean, really...

    Anyhoo, as you know, if the OP follows all of my advice, they will have a good night's sleep, and get the correct info from either the manufacturer, or with our assistance on here. Unless you have driven them away.

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