Safety device and method for an electric installation

A method for verifying safety implemented by a safety device connected between a circuit breaker device and an electric installation powered by an electric grid providing three-phase current having a first associated frequency, using a line for conveying electric current comprising three phase conductors, a neutral conductor and a protection conductor, making it possible to verify at least one electric safety condition following an electric power supply cutoff of the electric installation by the circuit breaker device, comprising:

• verifying a first safety condition for the presence of a residual voltage above a predetermined safety threshold on one of the phase conductors, when there is no residual voltage above the predetermined safety threshold, applying an isolation verification, capable of verifying the isolation between at least one tested pair of conductors of at least one pair of conductors, from among said three phase conductors in combination,
• and using at least one man-machine interface of the safety device to display a result upon each said isolation verification,
• wherein said isolation verification includes:
• injecting a high-frequency electric signal having a voltage below a voltage threshold, and a second frequency above the first associated frequency, only on a pair of conductors basis toward each pair of conductors to be tested that form the at least one tested pair of conductors.