How do contactless phase detectors work?

QHow can the contactless Phase Detector 3129 detect the phase without making contact with the conductor?


The Phase Detector 3129 uses a static induction voltage sensor. When clipped an insulated wire, this sensor can measure the voltage to earth by means of capacitive coupling, allowing the instrument to detect the voltage phase (R, S, or T), display a red lamp, and indicate the phase order. Unlike conventional phase detectors that had to be clipped directly to a live metal conductor, this product safely prevents contact and short-circuit accidents.