We all know that insulators carry charges much better than conductors. This is because conductors have much freer electrons than insulators, allowing electrical currents to form.

However, these two types of materials aren’t exclusive. In fact, one can rather easily turn an insulator into a conductor. This process is known as dielectric breakdown, and concerns a variable known as the dielectric strength of a material.

The dielectric strength of a material is the constant maximum electric field that a pure form of that material can withstand before it breaks down. When a material breaks down, it now becomes a conductor. In today’s circuitry, engineers have to be careful they don’t exceed the dielectric strength of the insulators they are using, or else the circuit may be in serious danger of overheating or simply functioning incorrectly.

Dielectric strength can also be altered. The factors which affect the strength are the thickness of the material sample, the temperature of the material, the humidity (for gases), and the frequency. For insulators, one can imagine, this strength is very high. However, it can be exceeded. Air has a strength of 3.0 MV/m, or 3,000,000 V/m. When an object’s strength is exceeded, it can often be seen with electrical sparks trailing off of it.

Below I’ve included an example of power lines exceeding air’s dielectric strength. Very visible electricity can be seen arcing through the air. That’s definitely something you don’t want to mess with!