why it is unsafe to leave switched on after use
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Answer:
That’s a myth from the last century, perpetuated by the odd scare story on the internet. Something my parents might have believed in the 1960’s, with more reason. We had valve radios and TV’s (vacuum tubes), which ran hot, had glowing filaments inside, and smelled like they were burning if they got too dusty. Now, we have a few cases widely reported of problems with new technology - lithium batteries in Samsung phones catching fire. A real problem, but by a few, I mean hundreds out of hundreds of millions of lithium-powered devices world-wide. The chances of it happening to you are one in millions. 200 years ago, when people used candles and oil lamps, you might have had a 1:1000 chance of burning your house down, each year.
Modern electronics and cables are made reliably by machines, and certified by national authorities such as UL, CSA, BS. Billions of people leave devices such as TVs in standby mode, powered up to listen for an infrared signal, and they hardly ever catch fire. There are much better things to worry about, such as whether your diet and exercise regime might be changed to give you another 10 years of life.
To be sure, “bad wiring” can cause fires - at least, that is cited by fire departments when they find charred outlets in burned houses. My belief is that those are due to overloaded circuits, worn/loose outlets, or damaged high-current cables. E.g. you run two electric heaters in an old rented apartment and the outlet overheats because the sockets do not grip the pins in the plug tightly enough, or you use an extension cord to power your whole home from a neighbor, and people damage the cord by tripping on it or driving over it or cover it with material so it can’t cool, so that you get an open circuit and arcing, or melted insulation and resistive heating like a toaster filament. A phone charger cable is not thick enough to support the power required to start a fire like this. My belief is that if you tried it - deliberately shorted out the cable - a modern charger would go into current-limiting or