The license which is being taken here regarding this issue, could cause the rating of a fuse to be misconstrued. A measurement in watts can not be applied and if license is taken in this regard, the measurement would be better broadly illustrated as watt hours. An extra level of work, expressed in watts can not be applied as a simplistic statement of fact.
Furthermore fuses do not blow in exactly the same manner and straight “deep engineering maths” can not be applied. Any suggested formulae must include an element of time, so that an entirely different unit of measurement becomes involved within the equation. This is accounted for within fuse engineering, and is sometimes expressed as Fp, i.e. pulse factor. For practical purposes, time verses current is best illustrated by means of a graph.
The applied voltage does not in a practical manner alter the rated value of a fuse link, as is expressed in amps, e.g. an automotive fuse is satisfactory for within a 12 or 24 volt circuit, and a fuse used in a domestic situation, 110 or 240 volts. Any expression of voltage in respect of current rating should be applied to the voltage drop across the fuse element, rather than that applied within the protected circuit and here time is of the essence.
In practice, voltage effects only the rupturing capacity of the fuse. The rated value is an indication of the current which can be carried without the fuse opening. When higher current is applied, over time, the fuse can be expected to burn out. The protective overload point is usually between 200% to 300% of rated value. How quickly this is reached, is decided by designed characteristics.
When the element as a result excessive current becomes heated to the point of maximum resistance, a destructive arc is formed. It is at this point that the element must effectively withstand and contain an explosion. Fuses designed for a high rupturing capacity, i.e. HRC fuses, include extra materials and have physical properties to this end.
