Fuse Blower

What happens if you plug too much into one socket strip? Switch on appliances, watch the current add up and see the fuse save the wire.

Mains voltage
Fuse
Switch on
Clock speed
Total power
60 W
Current
0.26 A
Fuse rating
13 A
Blows in
Never

The maths, live

Powers add up P = P₁ + P₂ + …P = 60 = 60 W
Current I = P ÷ VI = 60 ÷ 230 = 0.26 A
Heating in the wire ∝ I²(0.3 ÷ 13)² = 0.00 × its safe heating

Plug a kettle, a heater and a hair dryer into one strip. The fuse melts before the wire gets hot enough to catch fire. Now try it with no fuse!

How it works

Each appliance takes a current I = P ÷ V from the mains. On a multi-socket strip all the currents go through the same plug and flex, so they add up. Current heats a wire, and the heating grows with the current squared (I²), so twice the current makes four times the heat.

A fuse is a thin wire made to melt when the current is too big for too long. A small overload takes minutes to melt it, a big one only a fraction of a second. Once it melts the circuit is broken, so the flex never gets hot enough to melt its plastic or start a fire. Choose a fuse just above the current the appliance needs, like 3 A for a lamp and 13 A for a kettle.

Try this

  1. Switch on the kettle alone with a 13 A fuse. Does it blow? Now add the heater.
  2. Put a 3 A fuse in and switch on the hair dryer. How long does the fuse last?
  3. Try the overload with no fuse at all and watch the wire's temperature. Why is that dangerous?