A worked example of picking the correct plug fuse from an appliance power rating.
The fuse in a UK plug protects the appliance flex from carrying too much current, so it should be matched to the appliance rather than left as whatever came in the plug. This worked example shows how to choose it.
The rule. Find the running current from current = power / voltage, then pick the next standard plug-top fuse above that current. The standard fuses to BS 1362 are commonly 3 amps and 13 amps, with 5 amps also available.
Step 1 - a small appliance. Take a 500 watt appliance on a 230 volt supply. Current = 500 / 230 = about 2.2 amps. The next standard fuse above 2.2 amps is the 3 amp fuse, so fit a 3 amp.
Step 2 - a large appliance. Take a 2500 watt appliance on 230 volts. Current = 2500 / 230 = about 10.9 amps. The next standard fuse above 10.9 amps is the 13 amp fuse, so fit a 13 amp.
Step 3 - the principle. You choose the smallest standard fuse that is comfortably above the normal running current, so the fuse carries the appliance in normal use but still protects the flex against a fault.
Step 4 - why it matters to a plumber. Plumbing items such as pumps, immersion heaters and controls are wired and fused too, so getting the fuse right is part of safe, compliant work, and electrical work in a dwelling sits under the relevant building rules. Use the actual appliance rating and supply voltage, and follow the current guidance and the manufacturer instructions for the appliance.
Something wrong, unclear or out of date? Report an issue with this note.