The MN series motor protection switches are cam switches with thermal over-current trip devices integrated within the switch. The base unit forms the contact chamber with the cam wheel for function control. In the event of excess current, the bi-metals cause the switching latch to be operated via a trip shaft. This interaction enables a multitude of switching programmes with integrated motor protection to be produced. Due to the switching of the bi-metals within the current circuit there are 2 different series in terms of the setting ranges: for On/Off switches, reversing switches, pole-changing switches (1 rotary speed protected) and single-phase starter switches 12 setting ranges of 0.3 to 21.5 amps have been defined.
The star-delta switches are sub-divided into 7 setting ranges of 2.85 to 37 amps, with the bi-metals wired up in such a way that they are in the motor's phase current circuit. The motor coil is thus protected both in the star and the delta positions. The current to be set on the setting scale is the motor's rated current. No conversion is required.
Special cases
Star-delta switches for extremely difficult MN2Y start-ups are used where - due to the drive system – a long start-up period in the star position is required. So that the motor protection is not triggered during the start-up phase, the bi-metals are placed such that only in the delta position are they connected up in the current circuit. With this form of switching the motor is thus protected only in the delta position. Pole-changing switches – both rotary speed protected – MNDP. This switch has 6 bi-metals in it. 3 bi-metals are calibrated to the rated current at the lower rotary speed and to the rated current at high rotary speed. Changes via an adjustment scale are not possible. When ordering, the two rated currents at the lower and high rotary speeds must be precisely specified.
Build types
The MN series motor circuit breaker switches are made in the following build types: F front-fixing, LG iron-clad, CLG iron-clad with CEE connector plug, LT insulation-clad and CLT insulation-clad with CEE connector plug. Other build types are available on request.
Low-voltage circuit breaker:
Switching type 013
In the version with low-voltage triggering the MN switches ensure the protection called for in the EN 60204 provisions against automatic restarting when power is restored following a power cut. In the case of 013 switching, the 400V solenoid is between L1 and L2 and gets shut off at both poles. The nominal frequency is 50 Hz. Switches for other voltages with a frequency of 50 or 60 Hz can also be supplied on request.