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#138103 - 08/16/03 08:32 AM So much for UK 3amp plug fuses!
djk Offline
Member
Registered: 12/26/02
Posts: 1237
Loc: Ireland
Something interesting happened this morning.

I had a severe short caused by a cable being dammaged on my laptop power supply (it was squashed by a filing cabinate drawer)..

Simple 2 core cable, and due to the type of flooring there was obviously no leakage to ground so the RCD wasn't activated. (It was squashed between a plastic foot and plastic flooring so was fully insulated and there was no ground cable to cause a ground fault)

Noticed a slight burning smell and my desktop computer, printer etc went off as there was no power at the socket the 20amp MCB on the panel tripped out.

Worryingly or interestingly, im not sure which but the 3amp fuse in the plug was still in perfect working order!!!

Dud fuse? or just slow blowing?

Seems very inadequate protection on a 35 amp ring!!!
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#138104 - 08/16/03 08:07 PM Re: So much for UK 3amp plug fuses!
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
djk,
Does your laptop power supply have a box with a Transformer in it, to step down the voltage?, sometimes there is also a 3AG type fuse in this box, that protects the Primary side of the Transformer, but it sounds like if there was one, it never blew either.
It sure sounds strange how that 3A fuse never blew, mind you, the MCB at the Panel may have had a better Time/Current characteristic than the fuse, which I assume was an HRC type?.
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#138105 - 08/17/03 04:24 AM Re: So much for UK 3amp plug fuses!
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Some of the BS1362 fuses do seem to be rather reluctant to blow. I assume your MCB was a type B curve?

I've done a quick search to see if there are any time/current curves for BS1362 fuses online, but I couldn't find them. Here are the curves for BS1361 Fuses , the type used in British consumer units.
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#138106 - 08/17/03 06:57 AM Re: So much for UK 3amp plug fuses!
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
Loc: Stockholm, Sweden
Has anyone tested this on a ring circuit?
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#138107 - 08/17/03 09:00 AM Re: So much for UK 3amp plug fuses!
djk Offline
Member
Registered: 12/26/02
Posts: 1237
Loc: Ireland
Yeah, it's a B type MCB (Siemens to be precise)

Unlike an equivilant house in the UK this one has 9 X 20A radials rather than a couple of rings.

Wonder would that have blown a ring MCB?
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#138108 - 08/17/03 10:28 AM Re: So much for UK 3amp plug fuses!
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
Loc: Stockholm, Sweden
If a 3A fuse stays in working order on a 20A MCB, what would happen to a 5A fuse on a 32A MCB? Or a 13A fuse?

From Panelcomponents:

The fuse installed in all British plugs conforms to BS 1362 ("General purpose fuse links for domestic and similar purposes…"). The size of this fuse is 6.3 x 25.4mm. It has a breaking capacity rating of 6000A and is constructed with a sand-filled ceramic tube. The time-current characteristic on this family of fuses is not necessarily consistent with any other international standard, but it appears to have most of the characteristics of a fast acting fuse.

Here is an experiment: Does a 13A fuse blow on a modern ring?

By the way, why are the fuses 3A? The smallest wire size is 0.5 mm² which is good for twice that.

[This message has been edited by C-H (edited 08-17-2003).]
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#138109 - 08/17/03 11:52 AM Re: So much for UK 3amp plug fuses!
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Hmm.. I see another experiment for ECN testing labs, British branch coming up!

I don't know why the committees decided upon 3A as a standard rating, except that it's convenient for most small appliances up to around 750W.

These days, to simplify things for householders the recommended BS1362 fuse sizes are just 3 and 13A, even though many other sizes are available (most commonly 5A in general stores).

The original scheme, however, recommended that plugs be fitted with a 2, 5, 10, or 13A fuse as appropriate.
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#138110 - 08/17/03 12:29 PM Re: So much for UK 3amp plug fuses!
djk Offline
Member
Registered: 12/26/02
Posts: 1237
Loc: Ireland
Paul,

I remember seeing 16amp fuses to that spec on sale here in the 1980s !

They subsequently disappeared!

3KW appliences can pose problems here with 13Amp fuses particularly where the voltage is very definitely 220V.

I've also seen people simply wrap the live wire around the live pin by-passing the fuse.
Solder it onto it.

or even open up the fuse and replace the fusewire inside with a 16amp type instead!

I've also seen plugs with a peice of heavy guage cable saldered into the fuse carrier as the fuse kept blowing with appliences like tumble dryers.

Bypassing the fusing over here would generally only expose you to 20Amps though. so not quite as dangerous as in the UK.

Ideally here 3KW appliences need to be connected to a schuko or BS546 plug as 13amps is only barely enough.

It's become less of a problem as newer appliences are rated for 13amp max ( at 230V)
Older ones were designed around 16amp 220V so the maximum wattage is a little lower than it was 10+ years ago.


[This message has been edited by djk (edited 08-17-2003).]

[This message has been edited by djk (edited 08-17-2003).]
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#138111 - 08/19/03 05:29 AM Re: So much for UK 3amp plug fuses!
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
A few strands stripped from a piece of flex and wrapped around the fuse clips is another trick.

I've never seen a 16A fuse designed in plug size (1 x 0.25"). Such a device would certainly be non-compliant with BS1363, which specifies 13A maximum.

Coincidentally, some friends of mine had a chip fryer blow out a fuse yesterday. The socket was only on a 15A radial circuit, but the BS1361 consumer unit fuse opened leaving the 13A plug fuse intact.

There's not a big enough difference to guarantee discrimination there, of course, but it does point toward rather different curves for BS1362 fuses.
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#138112 - 08/19/03 05:30 AM Re: So much for UK 3amp plug fuses!
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
Loc: Norfolk, England
Note for our friends who aren't familiar with the British Standards:

BS1361 specifies the fuses used in distribution panels, rated 5, 15, 20, 30A and in increasing physical size to prevent overfusing.

BS1362 is the specification for the ceramic-bodied fuses used in our 13A plugs.

BS1363 is the specification for the 13A plugs and sockets themselves.
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