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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Every circuit has a “load” which usually is the thing doing work. It can be a motor, a lightbulb, or even just simple heater coil.
Loads are specifically designed to have a certain amount of resistance. A 1200W room heater will have thicker wire than a 600W room heater. The 600W heater has more resistance to choke down the current so it doesn’t overheat. A 1200W heater has less resistance to allow more amps through the device.
For instance, the standard outlet in a US home is 15A and 120V, so it has a breaker that will trip if you give it the full 15 x 120 = 1800W. Allowing for voltage spikes and appliances that draw a hair more amps than they should, the most powerful 120V microwave will typically be 1500W as a safety margin.
If you somehow bypass the full circuit (by going around the load) then, there is almost zero resistance, and huge volumes of amp-current will flow without any resistance. Hopefully the breaker will instantly trip, but if it doesn’t, the wire will get so hot it glows and then it will melt.
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