Petrenko's trick is to increase the electrical resistance in cables, something engineers usually avoid because it causes lines to lose energy as heat. Attached to each end of a line, his device switches the wires inside from a standard parallel layout to a series circuit. In normal conditions, the cable works like a standard power line, but flipping the line to series increases resistance, and the wires generate enough heat to shed the ice. The process takes 30 seconds to three minutes and saps less than 1 percent of the electricity running through the lines. Utility companies could switch the lines remotely, and Petrenko says swapping in his cables would cost less than repairing ice damage.