You can work out power using this equation:
P = I × V
P is the power in watts, W
I is the current in amperes (amps), A
V is the potential differences in volts, V
For example, what is the power of a 1.5 V lamp that draws a current of 5 A?
Power = 1.5 × 5 = 7.5 W
The equation P = I × V can be rearranged to find the current if the power and potential difference are known:
I = P ÷ V
For example, what current flows through a 1.15 kW electric fire at a potential difference of 230 V? Remember that 1.15 kW is 1,150 W.
Current = 1150 ÷ 230 = 5 A
Fuses come in standard ratings of 3 A, 5 A or 13 A.
The best fuse to use in this example would be the 13A fuse. The 3A and 5A fuses would blow even when the fire was working normally.