Protecting people from shocks has always been a priority in AC electrical system design. Equipment is typically designed to provide a barrier to anyone making physical contact with a live conductor, either through the use of insulation or other means. However, such contact can sometimes accidentally occur, causing what’s termed an ‘earth leakage’ or ‘residual’ fault current to pass through the person’s body. And it only takes 30 mA of current through a hand to the feet to cause death, unless the current is interrupted within a very short amount of time. Residual current devices (RCDs), or GFCI in North America, are designed to protect again this risk. However, there are new challenges due to the growth of electrical system applications, such as electrical vehicle charging stations, photovoltaic installations, and the wider use of variable speed drives for motor control. This has resulted in residual currents that are not purely sinusoidal. In this two-part blog post series, I’ll prov...