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If the appliance has 0.5 sq mm cable, the UK plug should (maybe "must" because of the wording in the Plugs and Sockets Regulations) be fitted with a 3A fuse, or 5A if high inrush.


If the appliance has 0.75 sq mm cable or above, the UK plug should be fitted with a 13 A fuse.


Before you get to selecting fuse size, you have already selected the cable based on the following (in Table 2 of BS1363-1 as mandated by the Plugs and Sockets Regulations):


Appliance Rating Cable Size
<=3A 0.5 sq mm or greater
<=6A 0.75 sq mm or greater
<=10A 1.0 sq mm or greater (0.75 is allowed if <2m cord)
<=13A 1.25 sq mm or greater


(noting the max size that will fit in a UK plug is 1.5 sq mm).


These rating figures are determined by the temperature the cable may reach in operation.


The fuse size is determined by using a "non-adiabatic" method, looking at whether the cable will overheat in a direct short-circuit.


The only limits on flex length (apart from 0.75 sq mm with a 10 A appliance) are relating to volt-drop (or Class I touch voltage), and not short-circuits.




So, how does this relate to your tin opener?


Assume current < 3A, manufacturer must choose flex not less than 0.5 sq mm (from Table 2 of BS1363-1). So he chooses 0.75 sq mm. Then needs to size fuse, and again refers to Table 2 of BS1363-1 which says that 0.75 needs 13 A fuse.


Manufacturer then ensures (with the aid of the appliance safety standard - in this case the appropriate parts of BS EN60335, I'd guess) that the tin opener will not cause fire or shock or burns in a fault with the selected fuse let-through, and presto - design complete.
 
Don't ever copy/paste complete replies written by other people from other forums.

It reeks of either you're misleading people into thinking the text is your work which is theft or fraud or you're starting a discussion using someone else's statements and opinions and they're not aware and aren't able to elaborate, expand, explain or defend their remarks that have been taken out of context.

The original thread is here IET Forums - What does a fuse protect!!!

This thread is closed and due for deletion in the near future.
 

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