Cable subjected to far more current than intended to illustrate what happens when fuses and circuit breakers are bypassed.
All cables will heat up when current is passed through them - this is due to the cable having resistance. In normal circumstances, the maximum current is limited to prevent the cable reaching dangerous temperatures. Devices such as fuses and circuit breakers are used to disconnect the power if too much current flows.
In this video, a 1mm² piece of twin and earth cable is subjected to various currents. This is normally rated to a maximum of about 16A.
Current is displayed on the yellow clamp meter, temperature on the smaller black meter.
At moderate overloads, the cable heats up causing the PVC insulation to soften and distort. This takes a few minutes.
At higher currents, smoke is generated as the PVC insulation burns away - the speed of smoke production increases with higher currents.
The final highest current of over 100A causes the cable to emit clouds of smoke almost immediately, before igniting with large flames. This represents what would happen to the wiring in your home if a fuse was bypassed and a short circuit fault occured.