A magnetic actuator comprises at least one coil surrounded by a magnetic circuit. The magnetic circuit possesses three legs and two facing end plates. The three legs comprise two outer legs on either side of the coil and an intermediate leg passing through the coil. The legs have no direct mechanical contact with one another. The two facing end plates magnetically interconnect the three legs. The magnetic circuit comprises a moving armature comprising at least one of the end plates, and a stationary portion including a yoke having at least the other one of the end plates and at least one permanent magnet. The permanent magnet is placed at one end of the intermediate leg beside the end plate of the yoke. The magnetic actuator can control medium-voltage and high-voltage circuit breaker vacuum chambers.