1Amp 240V Cartridge Fuses from here

[Murphyv310]

Hi.
Well we are all told the plug fuse is to protect the mains cable only. I'm somewhat sceptical about that statement as so many items have no internal protection at all.
The worry is often the mains switch if fitted, especially double pole types. Remember the Preh switches that Sony used? The many cheap rotary switches that BRC used and of course the ubiquitous 1uf 1000v cap across the mains, some of which were "before" the switch.
The scenario of course is the possibility of something breaking down, during that time a couple of amps being drawn and something catches fire, Joe public may have fitted a 13 amp or 5 amp fuse which merrily passes current till a full blown short blows the fuse.
There must be millions of electrical devices out there that are not properly protected by over rated fuses, we have the advantage here in the UK to be able to fit a fuse in the plug that is rated closer to the items requirements so although a 1 amp fuse may be still way in excess of that items current demand it has due to the aforementioned be a safer option.

[Terry]

Well we are all told the plug fuse is to protect the mains cable only. I'm somewhat sceptical about that statement as so many items have no internal protection at all.

Correct Trevor. If the device to which the cable is connected requires additional protection, it is the manufacturer's responsibility to provide it.

Don't forget that, especially today, the device is just as likely to be connected to a 16A Shuko connector protected by a 16A breaker irrespective of the rating of the mains cable.

This is in addition to the incorrect widespread use of 13A fuses in all UK plugs, irrespective of the cable rating. 

[ppppenguin]

In the old days in the UK a small appliance would likely be connected to a 5A rewireable fuse if you were lucky. Otherwise a 15A fuse.

Realisitically the plug fuse can only provide short circuit protection. In other words we hope the plug fuse blows before the cable blows. Even a thin mains flex should survive a 5A fuse blowing due to short circuit. I suspect a thin flex would "protect" a 16A MCB. It's all to do with the I^2 * t ratings of both the fuse/MCB and the cable. It may also depend on the loop impedance. A long piece of thin flex will limit the short circuit current considerably, thus reducing peak I but increasing t before the fuse blows.

Overcurrent protection is another matter. I think I more or less showed in a previous post that even a 1A fuse will provide pretty meagre protection against overcurrent. For the simple reason that even under fault conditions such as shorted turns the current is unlikely to be high enough to blow a 1A fuse quickly if at all.

Terry is entirely correct to state that the manufacturer is responsible for providing additional protection if needed. But remember we are often dealing with vintage equipment where designers didn't always get it right.

[Murphyv310]

 But remember we are often dealing with vintage equipment where designers didn't always get it right.

Hi.
Do we actually think that some of the tat sold these days is better than vintage gear?
Wall warts are a pet hate of mine, the number I have smashed open only to find no fuses, no fuse-able resistors, inadequately rated components is a joke.
One wall wart that was OEM on a Pure Evoke DAB radio that belonged to my sons mother in-law had partially melted when a fault occurred in the radio and went into overcurrent. It had welded to the 13a socket (unswitched) and after killing the mains all that could be done was to prise off the thing from the socket.
When I got it there was a burn up in the radio due to a leaky or shorted cap and the wall wart's mains transformer had burned out. Was there a fuse................. no chance!
Both Radio & PSU were binned!

I also have had a wall wart overheat, this was on a set of Christmas lights a few years ago, after an hour or so we could smell the classic plastic overheating fumes, the particular PSU was too hot to handle, in fact after pulling it out with oven gloves it was just getting soft. The following day when I looked at it (an open-able one) all it was, was a mains transformer, primary directly connected to the pins and the 24volt AC output to a din type two pin socket, no fuse and no thermal cut out embedded in the transformer, it must have had shorted turns as it got hot with no load.

So I'm sorry today's so called designers are no better than years ago. Perhaps our infatuation with so many items running with chargers, wall warts and the likes makes the problem more noticeable, in the days before the mid 60's say, there may have been one TV and one Radio so less to actually cause a fire or be a hazard. Lets also not forget chargers and wall warts have no ventilation, they are sealed and if a fault does occur the internal temperature can rise quickly and before you know it they burst into flames. An old Radio or TV due to its size and open construction would if a fault occurred be noticed quickly by those in the house by it either going off, smoke from a dropper or other signs, something that might not be seen bay a wall wart plugged in behind the curtain!

[EinsteinAGoGo]

As I've just changed the plugtop fuse on a Roberts RM50, from13A to 3A (lowest rating I've got in my fuse tray) I await Mr. Penguin's experiments with baited breath
I also had to move the cord-grip, from the insulated conductors, to the sheath, too.
Same as it ever was !

I think things may be slightly better now, but not much. In the old round-pin days, all appliances were festooned from a smorgasboard of Woolworth's adaptors, all plugged-in to the single (unswitched) 15A round pin socket in the room, but at least appliances were better (British?) made, and plugtops generally, were unfused.

My B&D cordless drill charger died not long ago, I opened the wall-wart to find no fuse, no protection, nothing, just a charred mess!

The fuse (or MCB, etc) is definitely there to protect the wiring; some years ago, I remember watching a guy apply first power to a control cabinet; the control circuit wire went up like the fuse in the opening titles of Mission Impossible!
Instead of connecting the control circuit wire to a 4A MCB, he had connected it to a 45A motor-rated MCB.
The MCB sat there quite happy....
Oh, how we laughed!

[ppppenguin]

I agree with Trevor that there's plenty of modern kit that's not adequately protected. For a wall wart the only real requirement is that it should stay safe under fault conditions. This could be done with a fuse, a heat sensor in the transformer (if not a switchmode), a PTC and there are probably other methods too.

Eisteinagogo's comment about control wiring reminds me of a clause in the wiring regs about how in certain cases, such as feeds from busbars to lower current circuits, these cables can ultimately be regarded as sacrificial.

[Terry]

So I'm sorry today's so called designers are no better than years ago.

In this modern day and age it is more likely that the designer included the protection but the bean counters took it out before the device went into production ...

[boater sam]

All street furniture wiring is deemed to be sacrificial. It is usually  1mm 2&e.

[ppppenguin]

Qualifying the point about sacrificial wiring, the sacrifice is for short circuit only, not for overcurrent. The far end of the cable must feed something with overcurrent protection (such as a fuse or MCB) or feed a load where overcurrent is extremely unlikely (such as resistive heating element which can't really suffer a large drop in resistance)

[Terry]

The official description is 'Street Light Cut-out' but in reality it is a large cartridge fuse holder ...