Electrical power and choosing fuses

The power of an electrical appliance can be calculated from the current that flows through it and the potential difference across it.

You can work out power using this equation:

curriculum-key-fact
power = current x voltage

P = I × V

Where:

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

Working out the best fuse to use

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.

Move on to Test
next