Short Circuits, Fuses and Safety

Lesson 8 of 10 · 7 min · Free, no account needed

What you will learn

A short circuit is a path with almost no resistance: the current shoots up, wires heat up, and the parts it bypasses go dark.
A fuse is a thin wire that melts above its rating and opens the circuit before the wiring gets dangerously hot.
Pick the smallest fuse above the working current (I = P ÷ V), and put it next to the supply. Mains wiring is a job for an electrician.

A fuse breaks the circuit on purpose. Why? First: if a bare wire joins the two ends of this bulb, what happens to the bulb?
Make the short: draw a wire that joins the two ends of the bulb.
Watch the bulb, the wires and the battery current.
Turn the heater up (less resistance) until the 3 A fuse melts.
The shortcut and the guard.
A short circuit is a path with almost no resistance. The current shoots up, wires heat up (P = I²R), and the parts it bypasses go dark.
A fuse is a thin wire that melts when the current goes over its rating, opening the circuit before the cables get hot enough to start a fire.
Mains electricity at home can kill. Fuses and cables there are a job for an adult or an electrician.
Find and fix the three dangers in this room.
Four 2 kW heaters on one strip draw about 4 × 2000 ÷ 230 ≈ 35 A, far over a strip's 13 A. Bare wire and water both give current a path through a person.
Game: Fuse picker. Give every plug the smallest fuse that will not blow.
UK plugs take 3 A, 5 A or 13 A fuses. Mains is 230 V, and I = P ÷ V.
Code: a smart plug does a fuse's job in software. Tap the line that decides when to cut the power.
Put the fuse where it protects every branch.
A fuse only guards the wires its current flows through. Next to the supply, before the branches, it carries the total current of every branch.
Before and after: a short in a house without a fuse, and with one.

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