Too many plugs? Fuses and electrical safety
Plug a TV, a kettle, a heater and an iron into one extension board. Watch the current add up, see the fuse blow when it gets too big, and learn why a fuse keeps your home safe.
Core concept
The current through a socket is the sum of the currents of everything plugged into it; a fuse melts and breaks the circuit when the current is more than the wiring can safely carry
Topic: Electricity
Every appliance needs electric current: The flow of electricity through a wire, measured in amperes (A). All key words to work, and the more powerful it is, the bigger the current: current (in amperes, A) = power (in watts, W) ÷ the voltage: The push that makes electricity flow, measured in volts (V). All key words of our mains, 230 V. When several appliances are plugged into one extension board, all their currents flow through the same socket and wire, so they add up. Too much current makes wires hot, and hot wires can melt their plastic covering and start a fire. A fuse protects us: it is a short, thin wire that melts when the current is more than it is made for, breaking the circuit: A complete loop that electricity flows around, from the cell through the bulb and back. All key words before the wires overheat.
What you will learn
- Work out the current an appliance draws from its power: current = power ÷ 230 V.
- Explain that the currents of appliances on one socket add up.
- Explain how a fuse protects the wiring from overheating.
- Follow safety rules for sockets, extension boards and fuses.
Before you start
- Know that electric current flows in a closed circuit.
Materials
- Pictures or labels of appliances with their power in watts
Equipment
- A model extension board (never experiment with real mains electricity)
Procedure
- Plug in only the TV and record the current.
- Plug in the kettle as well and record.
- Plug in the heater too and record.
- With a 5 A fuse, plug in only the kettle and record.
How this simulation is simplified
- The mains voltage is 230 V, as in Nepal.
- Each appliance draws its full rated power while it is plugged in and on.
- The fuse melts as soon as the current is more than its rating.