Siemens SAMMS-MV User Manual

3 Operating the SAMMS-MV Device

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.

3.12 Protection 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 I

FLC

. (The typical starting current of

motors is 600% of I

FLC

.) For example, an overload class setting

of 10 guarantees that a current of 600% of I

FLC

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 I

FLC

The lowest overload class, greater than or equal to the motors

starting time, gives the best protection. Overload classes 2

through 23 are available in SAMMS-MV. The range of protec-

Important: In the unlikely event that the motor acceleration time

(overload class) exceeds the motors 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.

Figure 3.6 Rotor and winding temperature during 10 second motor stall