2.5 know and use the relationship: power = current × voltage P = I × V and apply the relationship to the selection of appropriate fuses

Formula:

power = current x voltage

Power is measured in Watts
Current is measured in Amps
Voltage is measured in Volts

This equation is used to calculate what fuse value (in amps) you will need for that specific appliance

The formula can be rearranged to form:

current =  power
                voltage

voltage =  power
                current

Examples:

1. In a lightbulb that is given 230 Volts and has a 2 Amp current, give its power.
2. In a kettle that uses 300 Watts of power and has a 1.5 Amp current, state its voltage.
3. What current does a toaster have that uses 40 watts of power and 20 Volts? What fuse value would it therefore need?

Answers:

1. 230 x 2 = 460 Watts
2. 300 ÷ 1.5 = 200 Volts
3. 40 ÷ 20 = 2 Amps  so a 3A fuse would be used

Fuse values come in 3A, 5A and 13A and you would always choose the one closest to the current, unless it is with 0.5A of the limit. e.g a 2.8 A appliance would probably need a 5A fuse.