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Old 9th Jul 2019, 4:34 pm   #101
kalee20
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Default Re: 13 amp fuse for 1.5mm mains flex?

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Originally Posted by rambo1152 View Post
... that shouldn't preclude us from putting in a lower value to give added protection to the appliance.
Well there are those who argue that it should. The appliance is supposed to be fully protected in and of itself ('fully' in the sense of having no need at all for additional protection).
I'd side with Rambo here. A bit of extra protection never comes amiss. I have appliances which have no internal fuse at all (vintage radios) and some which might have but I can't see anything (some modern stuff).

If I have a table lamp, (for which a 1A fuse is technically appropriate but the label underneath might say 3A on the basis that 3A and 13A are the two values commonly sold in the shops), and the lead gets a bit frayed, and I replace it but only have 1.5mm▓ available so use that, I wouldn't then expect to replace the fuse with a 13A type on the basis that 'the fuse is only there to protect the cable, not the appliance, and it is bad practice to "fuse down" below the cable rating.'
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Old 9th Jul 2019, 4:58 pm   #102
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Default Re: 13 amp fuse for 1.5mm mains flex?

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I once has a 13A to shaver adapter that was fused at 1A.
I can't remember the fuse length now though.

I have one here, it's 20mm or 3/4 in

I borrowed one from a Premier Inn reception once and the fuse was wrapped in tinfoil.
As I'm interested in this sort of thing, I picked up an adaptor to convert a BS1363 plug to a Shucko receptacle.
There was a neatly lettered notice on it, " Concierge Deposit 50P".
I'm sure, it was worth more than 50P.
Dave, USradcoll .
I made a mistake on my entry. The adapter converts a BS1363 receptacle to a NEMA 5-15 plug. It's equipped with a BS1362 13A fuse. Fine Quality device. Dave US radcoll1
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Old 10th Jul 2019, 3:04 pm   #103
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Default Re: 13 amp fuse for 1.5mm mains flex?

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Like magic I have rustled up one in retail packaging for a quick tear down....
The socket strip itself is a bodger's special with shutters that can be opened with the earth pin of any 13A plug.
As chance would have it, I have just come across a potential hazard with these socket strips. I pulled this one pictured out from under some furniture at a relative's house, and it literally fell to pieces in my hand. There had been a transformer-wall wart for a little used DAB radio left in it, amongst other things. I presume the heat of the tranny over a decade or so must have helped weaken the plastic, but even the farthest sections could be pulled apart with practically zero effort. Don't recognize the brand, likely a supermarket or pound shop special.

I advise anyone with such a strip into which older wall warts are left connected to check it, to be on the safe side.
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Old 10th Jul 2019, 3:58 pm   #104
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Default Re: 13 amp fuse for 1.5mm mains flex?

In my experience fuses blow for two reasons, old age or a (possibly intermittent) short-circuit somewhere.

I have a 3kW fan heater which probably draws in excess of 13A. The fitted plug overheated destroying itself and the socket it was plugged into, but the plug fuse remained intact. There've been no problems with the replacement MK plug which was salvaged from a scrap item.

As for extension leads I've seen several which have melted as they haven't been uncoiled before a heavy load was applied.
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Old 10th Jul 2019, 4:31 pm   #105
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Default Re: 13 amp fuse for 1.5mm mains flex?

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In my experience fuses blow for two reasons, old age or a (possibly intermittent) short-circuit somewhere.

I have a 3kW fan heater which probably draws in excess of 13A. The fitted plug overheated destroying itself and the socket it was plugged into, but the plug fuse remained intact.
Yes, fuses can handle surprising overloads: not that long ago I bought a new washing-machine whose heater is rated at 2Kilowatts. Because I was doing some kitchen-refurb work it stood next to the sink rather than being fitted into its proper space, so I powered it via a 2-way trailing 13A extension-lead which was also temporarily powering the fridge.

It did three washes before the 3Amp fuse in the extension-lead's plug failed!
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Old 10th Jul 2019, 5:26 pm   #106
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Default Re: 13 amp fuse for 1.5mm mains flex?

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Like magic I have rustled up one in retail packaging for a quick tear down....
The socket strip itself is a bodger's special with shutters that can be opened with the earth pin of any 13A plug.
As chance would have it, I have just come across a potential hazard with these socket strips. I pulled this one pictured out from under some furniture at a relative's house, and it literally fell to pieces in my hand. There had been a transformer-wall wart for a little used DAB radio left in it, amongst other things. I presume the heat of the tranny over a decade or so must have helped weaken the plastic, but even the farthest sections could be pulled apart with practically zero effort. Don't recognize the brand, likely a supermarket or pound shop special.

I advise anyone with such a strip into which older wall warts are left connected to check it, to be on the safe side.
That one has a different styling to the one I showed in post#52 so hopefully mine will last a bit longer.
We will just have to be careful to unplug the things from the wall socket before changing plugs over after they have been in use for an extended period and keep a few recently bought ones handy as replacements for when they fall to bits.
It is not the first photo I have seen of one that has fallen apart.
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Old 10th Jul 2019, 6:02 pm   #107
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Default Re: 13 amp fuse for 1.5mm mains flex?

It's not just socket-strips that fall apart with age: in the past I've had the covers pull-off elderly 13A plugs when trying to withdraw them from their sockets.

This is either because the cover-retaining screw is tapped straight into the cover - and the boss where it's tapped-into splits, or in some cases the little brass bush fitted in the cover pulls-out of the cover.

(this second failure seems more common in 'rubber' plugs - I guess the rubber hardens/shrinks with age).
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Old 10th Jul 2019, 7:06 pm   #108
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Default Re: 13 amp fuse for 1.5mm mains flex?

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It's not just socket-strips that fall apart with age: in the past I've had the covers pull-off elderly 13A plugs when trying to withdraw them from their sockets..
This is one of the more serious flaws in the BS1363 plug design. You could easily have a situation where the top of the plug is detached, leaving exposed live terminals. I have seen this on several occasions. Especially lethal in an unswitched socket. This is where the Schuko type seems superior, as you usually have to clasp both halves together as you withdraw it, the halves being at 90║ to the wall socket.
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Old 10th Jul 2019, 11:08 pm   #109
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Default Re: 13 amp fuse for 1.5mm mains flex?

Watch this
https://www.dropbox.com/s/dq2w6z5r4m...14353.mp4?dl=0
"Chris B" who uploaded that in 2016 gives the following information:

For info printed on the bottom was
BLS114
BS1363A
Total load not to exceed 13A

And a sticker which said 20070725 (Which I suspect is the date of
manufacture).
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Old 11th Jul 2019, 12:03 am   #110
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Default Re: 13 amp fuse for 1.5mm mains flex?

That is exactly what happened in my case Graham. Truly appalling materials and build quality.
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Old 11th Jul 2019, 5:48 am   #111
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Default Re: 13 amp fuse for 1.5mm mains flex?

Quote:
If I have a table lamp, (for which a 1A fuse is technically appropriate but the label underneath might say 3A on the basis that 3A and 13A are the two values commonly sold in the shops), and the lead gets a bit frayed, and I replace it but only have 1.5mm▓ available so use that, I wouldn't then expect to replace the fuse with a 13A type on the basis that 'the fuse is only there to protect the cable, not the appliance, and it is bad practice to "fuse down" below the cable rating.'
I don't think anyone is saying it is inherently bad practice to use a fuse of lower rating than the cable. Your table-lamp example is a fixed load that will never approach 3A, so there is no disadvantage in fitting a 3A fuse. However, where the possible future load is unknown, such as in the OP's extension lead or a cordset, an undersized fuse might unintentionally be subjected to a prolonged low overload. A 1.25mm▓ extension cable fitted with a 5A fuse 'because it is only powering AV equipment' might in the future be used for a 2kW load. The fuse will not blow, but the plug will be subjected to unnecessary extra heating.
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Old 3rd Aug 2019, 5:14 am   #112
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Default Re: 13 amp fuse for 1.5mm mains flex?

I don't trust fuses generally. In the IEE's "A Practical Guide to the Wiring Regulations" it says somewhere -

"..for example, for a 30A circuit protected by a 30A rewirable fuse and drawing an overload current of 60A, disconnection on overload may take up to 4 h. ."

I'm not sure what they mean by "rewirable fuse", but I suspect it includes both the old fusewire and cartridge fuses, as opposed to modern circuit breakers. If a 30A fuse can survive 60A for 4 hours before rupturing, then presumably a 13A fuse in a plug isn't going to disconnect instantly – or even quickly – even with a significant overload.

Mike

Last edited by Boulevardier; 3rd Aug 2019 at 5:21 am.
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Old 3rd Aug 2019, 9:08 am   #113
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Default Re: 13 amp fuse for 1.5mm mains flex?

'Rewirable fuse' refers specifically to a semi-enclosed fuse where a length of bare wire is manually installed in the carrier, made to BS3036 or similar design. These are taken to have a fusing factor of approximately 2, i.e. the current at which the fuse is guaranteed to operate is 2x In, the rated current that it can withstand continuously without its lifespan being shortened.

HRC (high rupturing capacity) cartridge fuses have generally better characteristics including tighter control of nominal current and much lower fusing factor, which is taken to be 1.45 for normal HRC types and is similar to that of MCBs. This difference in performance is reflected in the correction factors for determining the applicable current rating of installation cables, where an additional derating factor Cr = 0.725 is applied to allow for the high fusing factor of rewirables. In other words, where a cable is protected by a rewirable fuse rather than an HRC cartridge, it must have a continuous rating of 2/1.45 = 1.38 times higher, to allow for a particularly lethargic response from the fuse.

It is disingenuous not to 'trust' fuses. There are many applications in which they significantly out-perform circuit breakers and are still the devices of choice. One might argue that it is circuit breakers that should not be trusted, reliant as they are on a mechanism of levers, springs, plastic mouldings, heaters and solenoids, equipped with no means of routine testing, that might languish for years slowly seizing up until called upon to operate in a fraction of a second. In contrast a fuse relies on just a simple law of physics (P=IR), plus the unchanging resistivity and melting point of copper, and is known to become more sensitive as it ages rather than less making it inherently fail-safe.
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Old 3rd Aug 2019, 9:19 am   #114
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Default Re: 13 amp fuse for 1.5mm mains flex?

HI Mike,
A rewirable fuse (classed as a semi enclosed fuse BS3036) is different from cartridge fuses. Rewirable fuses have less precise characteristics than cartridge fuses and different rules apply to the ratings of cables protected by them.

Looking at the time- current characteristics for different protective devices in the wiring regs shows:

30A rewirable fuse at 50A won't blow at all. At 60A it will take 100 seconds and at 100A it will take 3 seconds to open.

32A cartridge fuse (BS88) at 50A will take 50 mins. At 60A it will take 6 mins and at 100A it will take 10 Seconds to open.

32A type B circuit breaker at 50A will take 16 mins. At 60A it will take 3 mins and at 100A it will take 30 Seconds to open.

Fuses and circuit breakers must be the most mis- understood devices and there is a wide assumption that they trip at exactly the rated current.

So the object in an electrical installation is to ensure under fault conditions that sufficient current flows to open the protective device quickly enough. Loop impedances are key to this.

Lower current overloads are difficult to deal with and cause overheating of the cables so circuits should be arranged to minimise the chance of prolonged overloads.

13A fuses are particularly bad. They get too hot at 13A but will sit there all day at 20A. The plug or spur will melt long before the fuse will blow! Look up the time current characteristics for them!

Hope that might be of interest

All the best
Nick

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Old 8th Aug 2019, 12:35 am   #115
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Default Re: 13 amp fuse for 1.5mm mains flex?

Thanks Nick - that's very interesting - and worrying. I knew that fuses weren't exactly precision devices, but I didn't realise it was that bad. Dead shorts are one thing - and you can hasten the fuses' rupture by ensuring very low earth-loop impedance to the extent that their death is almost instant. But a 13A fuse in the plug for, say, a faulty hair-drier that has a fault but not a dead short, could sit there all day having 20A pulled through it - and through the hair-drier.

Put that together with the shortcomings in circuit breakers outlined by Lucien , and there doesn't seem much hope for any of us! And I thought my wiring was safe...!

Mike

Last edited by Boulevardier; 8th Aug 2019 at 12:55 am.
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Old 8th Aug 2019, 11:48 am   #116
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Default Re: 13 amp fuse for 1.5mm mains flex?

Quote:
But a 13A fuse in the plug for, say, a faulty hair-drier that has a fault but not a dead short, could sit there all day having 20A pulled through it - and through the hair-drier.
This is not a likely scenario, with modern appliances anyway. The plug fuse is primarily to protect the flex and plug in the event of a short-circuit fault. The appliance is required to have its own protection against overload or dangerous malfunction. In the case of the hairdryer, there will probably be two separate devices; a self-resetting thermal trip and a permanent, non-resettable thermal fuse. Any fault that causes the hairdryer to draw a dangerous current through its flex and plug will cause one or both of those to operate, as it would be dissipating much more heat than it is designed to do. Importantly, the prtoection is detecting the hazardous condition itself, namely overheating of the hairdryer, which can occur in other ways too such as restricted airflow. This makes is by far a better solution than relying on a fuse to sense the corresponding overcurrent.
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Old 9th Aug 2019, 8:15 pm   #117
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Default Re: 13 amp fuse for 1.5mm mains flex?

This has turned in to a very interesting thread, thank you for all the replies.

I opened up my Teac cassette deck out of curiosity to see where the internal fuses are located, and strangely I can't locate them. Maybe they are hidden under the circuit boards near the transformer, but I am not going to dismantle it to find out.

I use a five amp fuse, which is plenty for the power cable, but I was also curious to see how many amps the internal fuses are. Could it be possible my cassette deck has no internal fuses ? It would seem odd if this is the case.
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Old 9th Aug 2019, 9:15 pm   #118
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Default Re: 13 amp fuse for 1.5mm mains flex?

There are cases where the protective device is embedded in the mains transformer's primary winding. It's not serviceable so if it blows then the transformer is a write-off. As long as this happens sufficiently infrequently I imagine it can be cheaper for the manufacturer than wiring in an accessible fuseholder or, perhaps, soldering a wire-ended fuse into a pcb.

Cheers,

GJ
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Old 9th Aug 2019, 10:29 pm   #119
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Default Re: 13 amp fuse for 1.5mm mains flex?

Thanks for the information.

Model is Teac V -3000 cassette deck. It is a three head model. A very good machine.

Placing the fuse embedded within the transformer windings is something I have never heard of. Is this a cheaper option than using changeable fuses ?

For a machine of this quality, it seems a strange choice. Once the transformer goes, it will be cheaper to buy a replacement deck second hand.
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Old 9th Aug 2019, 11:35 pm   #120
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Default Re: 13 amp fuse for 1.5mm mains flex?

Philips sometimes fitted replasible thermal fuses in transformers.
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