Magnetic trip device with wide tripping threshold setting range

A magnetic trip device with a wide tripping threshold setting range, comprising a fixed magnetic circuit bearing an excitation coil and having a first and a second polar part located one in the extension of the other and separated by a fixed air-gap and a moving core assembly, slidingly mounted inside said fixed magnetic circuit and having a first part of the core assembly with a polar surface defining a first variable air-gap with said first polar part, the value of which varies with the movement of the moving core assembly, wherein said moving core assembly comprises a second part mechanically united to the first part, and magnetically insulated from the latter, said second part defines with said second polar part a second variable air-gap, the attraction effects exerted on the moving core assembly by the magnetic fields generated by the coil in said first and second variable air-gaps being opposing, and an adjustment device is arranged to fix the initial position of the moving core assembly and to adjust the tripping threshold appreciably linearly.