Mitsubishi Electric MEsoftstart/I01 Users, Installation & Instruction Manual page 12

Typical operating temperature
The operating temperature is determined by the typical ambient temperature in the immediate vicinity of the soft starter, air
flow through the soft starter and cooling mechanisms that are used, as well as the soft starter workload. Refer par 2.2.3 for a
description of how the cabinet design can also be used to best regulate operating temperature.
De-rate the soft starter starting capacity at 1.4% per °C for higher temperatures above 50°C.
Example of temperature de-rating:
The requirement is for a 75kW 400Vac motor (normal, 3-wire connected) in a heavy duty application, to operate in an
environment where the operating temperature is likely to be 60°C. From Table 2, the motor's FLC = 136A (at 0.8 power
factor), while the MEsoftstart/I01 model soft starter can provide a maximum starting current of 184% (or 250A) if operated
below 50°C.
These values should be de-rated for operation at 60°C i.e. (60°C - 50°C) * 1.4% = 14%, thus 184% - 14% = 170% (or 231A).
If this is insufficient for the application, then more robust selection for this application may be MEsoftstart/I02 with a de-
rated starting current of 287% - 14% = 273% (or 371A) – see Table 3.
Soft starter workload
Soft starter workload is made up of the starting time, stopping time and number of starts per hour, as well as any run time when
a bypass contactor is not used. If the expected work load is high, a soft starter with a larger current margin should be selected.
If the expected starting time is longer than 30 seconds, a higher rated soft starter should be selected. If the application requires
frequent starts with short running time, select a soft starter from the heavy duty columns.
Figure 1 –Normal and Heavy duty applications as defined by soft starter on-time
12 Introduction