Selection Example - Siemens SIRIUS Manual

Configuration
6.2 Use of 3RA2 load feeders with highly energy-efficient motors (IE3)

Selection example

In this example, two motor starter protectors are compared with each other.
Rated motor current: 15 A
Motor starter protector A: Setting scale 10 ... 16 A
Motor starter protector B: Setting scale 14 ... 20 A
Motor starter protector B (14 ... 20 A) is recommended since its power loss is lower and it
has a higher distance to the response limits.
The power loss of motor starter protector B is approximately 35 % lower than that of motor
starter protector A.
The response limits of the short-circuit release always refer to the maximum setting value:
● In the case of motor starter protector A, the response value of the short-circuit release is
208 A (13 × 16 A).
At the setting value of 15 A, the distance to the response limit of the short-circuit release
is 13.86 times the current setting (208 A / 15 A =13.86).
● In the case of motor starter protector B, the response value of the short-circuit release is
260 A (13 × 20 A). With a setting value of 15 A, the distance to the response limit of the
short-circuit release is 17.33 times the current setting (260 A / 15 A = 17.33).
In the present example, the distance to the response limit of 13.86 times the setting current
for motor starter protector A increases to 17.33 times the current setting for motor starter
protector B.
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SIRIUS - SIRIUS 3RA load feeders
Manual, 09/2016, A5E03656507520A/RS-AB/003