Originally Posted by
Chris Padilla
Well, finally something I think I can add to the conversation. So, as has been stated, the size (diameter or more correctly, cross-sectional area since its a volume of metal that the current flows through) of a wire (copper or otherwise) will determine the amount of amperage it can handle before melting or getting too hot to cause other problems. Or as a power company sees it, they want as small a current as possible so they can use as small a wire as possible to save as much money as possible. This is why power lines run in hundreds of thousands of volts and why they use step-down transformers to bring the couple hundred volts into our businesses and homes. As to the insulation on the wire, that is a voltage or more correctly, an electric-field issue. It is known as dielectric breakdown or dielectric strength and is measured in Volts/meter (V/m). There is a particular field strength that a material can handle--usually done on an insulator or a dielectric--before it is no longer an insulator. At the atomic level, the field strength rips normally tightly-bound electrons free from the insulator and it begins to conduct. Once this happens, the insulator is basically destroyed. We all see it burning/melting of the insulator. I'll also note that high voltage power lines are not insulated: costs money and their voltage levels are very high. However, air is also a dielectric/insulator and air also will break down if the field strength is high enough. I think air is around 3 million V/m. I've never heard of a power company running much higher than 800,000 V. But lightning can hit many millions (even billions) of volts so that is why we see it: air is being broken down, electrons ripped from their source, and current flowing--a bolt!
