A sensor unit coupled to a first wire of a power line for measuring power-related parameters of the power line. The sensor unit contains a first capacitor and makes voltage measurements relative to another wire, to which the sensor unit is coupled by a second capacitor. The captors form a voltage divider such that the sensor unit may measure a voltage in a range much lower than the voltage on the power line. Additionally, the capacitive voltage divider yields a voltage that can be used to power the sensor unit, including by charging an energy storage device. The sensor unit may also supply power to other nearby devices, such as other devices that form a mesh sensor network.