Is there another factor at play here which I am missing? Or do I just have the wrong fusing factor! The current (I2) causing effective operation of the protective device is given in the product standard or may be Now I did not quite use Chris's figure of 3 mins at 20 A, but if I had it would have scaled to 3mins/100 at 200A, or about 2 seconds for a 40 degree rise. I had a more optimistic figure, allowing a bit for the PVC, and as I did not have the regs with me, so used a pidooma figure from memory. Well a 13 A fuse will carry 13A all day, and may not blow in any sensible time even at 20-25A, depending on manufacturing tolerances and environmental temperatures.

In reality only AWE or CERN will install a cable in vacuum like that, and of course any real cable will heat quite a lot more slowly. The operating characteristics of a device protecting a conductor against overload shall satisfy the following conditions: If too large a current flows through a lead it may overheat or catch fire, making the main purpose of a domestic plug fuse to prevent fires due to large currents. The fuses have the ASTA approval symbol and appear to be branded 'CF' and marked AF63. (A BS1362 fuse must have the manufacturer's name or identifying mark.) They also have a number printed on them: SS157. ii) the rated current or current setting of the protective device (In) does not exceed the lowest of the currentcarryingThe fuse wire is a flat tape rather than round wire. In comparison with a 13A fuse wire, it’s considerable larger. The length of the fuse measures 24.91mm. A BS1362 fuse should have a length of 25.4mm with a tolerance of +0.8/-0.4mm. The rated current may be any value not exceeding 13A. For use in plugs, the preferred rated currents are 3 A and 13 A." The shiny metal end caps are also a good indicator that the fuse is not genuine. The end cap on the genuine Cooper Bussmann fuse is not as shiny. This fake fuse also has a larger than normal dimple in the end of the cap.

I was able to rustle up a short length of 2.5mm cable off the end of a reel, and the use of another car battery from an alarm engineer.The outcome of all this is to not worry about these minor domestic overload problems, as one can see from the normal use one sees, they rarely cause any trouble at all. Loose connections are the cause of problems, not overload of cables. The operating characteristics of a device protecting a conductor against overload shall satisfy the The rated current or current setting of the protective device (In) does not exceed the lowest of the current carrying (Iz) of any of the conductors of the circuit, and Part 2: Overcurrent: A current exceeding the rated value. For conductors the rated value is the current carrying capacity. The fusein a plugis a deliberate weak link in a circuit which will 'blow' if an electrical appliance or extension lead draws too much current due to either an overload or a fault.

At the beginning, 100% of the heat generated in the live conductors is available to heat the cable. At 21 deg C, only 98% of the heat is available because the loss is 1/50 of the amount at the steady state. At 22 deg C, only 96% is available and so on. So looking at 1 deg C increments, it takes in fact 45 min to get to 69 deg C and you never quite get to 70 deg C. Please forgive me for having forgotten the calculus which I learned 45 years ago.

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NOTE 2: Protection in accordance with this regulation may not provide protection in all cases, for example, where sustained iii) the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of The wire inside a fuse heats up when a current passes through it. The more current that passes, the hotter the wire will get. If the current is high enough, the wire will melt and cut the power to the appliance. The rated current of the fuse, in this case 13A, is the current that it can safely pass whilst maintaining a low enough temperature not to overheat the plug. BS 1362, the British Standard for the fuses used in plugs, specifies a maximum power dissipation of one watt when carrying the rated current.