Plug wires and fuses
A UK three-pin plug has a live wire (brown, carries the current), a neutral wire (blue, completes the circuit) and an earth wire (green and yellow, safety). A fuse melts if the current is too high.
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Analogy
A fuse is a sacrificial link: it breaks so the appliance does not burn.
Example
power = 920 W, voltage = 230 VI = P / V = 920 / 230 = 4 AFuses come as 3 A, 5 A, 13 A.Choose 5 A.
In practice
A 3 A fuse for a lamp, 13 A for a heater. Choose the fuse just above the normal current.
Practice
Flashcards
- What is the colour of the live wire?Brown.
Interview questions
- A hairdryer is rated 1,150 W and works on 230 V mains. Work out the current and choose a fuse from 3 A, 5 A and 13 A.
- I = P / V = 1,150 / 230 = 5 A
- Fuse must be just above the working current
- A 5 A fuse would blow in normal use
- Choose a 13 A fuse
Questions people ask
What does a fuse do?
A fuse contains a thin wire that heats up and melts if the current goes above its rating. This breaks the circuit and stops the current before wires overheat and start a fire. A 13 A fuse will melt if the appliance draws far more than 13 A.
What colour is each wire in a UK plug?
The live wire is brown, the neutral wire is blue, and the earth wire is green and yellow stripes. The live wire carries current from the supply, and the fuse is fitted on it. Mixing the colours up is dangerous, so always check them when wiring a plug.