I know what a short circuit is and how to make that happen. But what actually happens? Why does low resistance in a circuit causes the conductive material to become so hot?
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The ideal assumption we would use in studying a first or second year circuits class is that wires have 0 resistance. That’s usually a close enough approximations for simple circuits. In real life, wires do have resistance. Let’s say a 20 foot piece of wiring in your walls has 4Ω of resistance. In a short circuit scenario, there is 120 volts across 4Ω which means it tries to draw 30 amps of current.
That would pop most breakers, but there are 30A breakers. If no other devices on that circuit are drawing any current, then potentially, the breaker would allow that 30 amps to flow through that 4Ω wire. If you remember, power is current squared times resistance P=I²R so this wire is drawing 3600 watts. A resistor dissipates pretty much all it’s energy in heat. (If the heat is high enough, you also get light) so basically, you’ve created a 3.6 kW space heater in your walls.
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