Abstract: The present invention provides a three-dimensional electric field sensor for hard hats, the sensor having a stand-alone structure and constructed of polymeric and hydrophobic materials, and intended for three-dimensional measurement of the electric field in energized powerlines by its disposition on hard hats. The three-dimensional sensor of the present invention has an outer shell with a base attaching to the hard hat and a cover attaching to the base, an inner shell functioning as a capacitive sensor as well as protecting an internal electronic board, a battery and adapter assembly as a power supply, and a warning buzzer, in order to provide complete optimization procedures to alert electric utility linemen of exceedingly close proximity to medium voltage conductors in powerlines.