Siemens SAMMS-MV user manual Protection Curves and Overload Classes

3 Operating the SAMMS-MV Device

Figure 3.6 Rotor and winding temperature during 10 second motor stall

temperature. You can select ambient temperature from 0° to 70°C in increments of 5°C, with HHC function F0.

Important: Do not use this feature with motors rated for ambient temperature other than the standard 40°C.

3.12Protection Curves and Overload Classes

The specific motor protection curve selected depends upon the overload class setting. The overload class is defined as the maximum tripping time in seconds for a current level of 600% of the full-load current or IFLC. (The typical starting current of motors is 600% of IFLC.) For example, an overload class setting of 10 guarantees that a current of 600% of IFLC will cause a trip in 10 seconds or less. In the SAMMS-MV, the protection curves

are designed to cause a trip in 90% to 100% of the class time for a current of 600% of IFLC.

The lowest overload class, greater than or equal to the motor’s starting time, gives the best protection. Overload classes 2 through 23 are available in SAMMS-MV. The range of protec- tion curves are shown in Figures 3.7 through 3.10.

Important: In the unlikely event that the motor acceleration time (overload class) exceeds the motor’s stall time, use a speed switch as an input source to open the contactor if the switch senses a locked rotor or stall condition.

Note: For clarity, the time-current characteristic curves in this manual are shown with overload classes 2, 5, 10, 15 and 23 only. Use interpolation to derive values of other overload classes not shown.

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