Electrical principles
Power in watts is voltage times current, and how a circuit is wired decides what happens when one part fails.
A worked example
A 240 V element drawing 6.0 A uses P = 240 x 6.0 = 1 440 W, which is 1.44 kW.
The mistake people actually make
Voltage is the push and current is the flow, so a high voltage on its own does not mean a large current. Fitting a heavier fuse removes the protection rather than fixing the fault.