Motor control centre cabinet design
A soft starter unit uses semiconductor devices. To ensure reliable operation and long service lifetime for the soft starter, it is
important to operate the soft starter in the ambient environment that complies with the equipment specifications.
When designing or selecting a soft starter cabinet, the structure, size and device layout inside the cabinet should be determined
by considering issues such as:
Safe and easy access for wiring;
Safe and easy access to the HMI for configuring and monitoring;
Heat generation and cooling of the soft starter;
Peripheral devices that need to be in the cabinet and
The operating environment.
Minimum cabinet size
The minimum cabinet size should be decided upon by considering the following:
a) The circuit layout with peripheral devices (refer par 2.1);
b) The installation environment (refer paragraph 2.2.2);
Air flow requirements of the soft starter (refer par 2.3.3);
d) Cooling requirements inside the cabinet (refer paragraph 2.2.3);
e) Minimum space required around the soft starter (refer par 2.3.3).
Soft starter installation environment
The following table lists the standard specifications of the soft starter installation environment.
Using the soft starter in an environment that does not satisfy these conditions, will deteriorate its performance, shorten its life
span and can lead to failure. The following paragraphs contain suggested measures to ensure that the environment complies
with the specification.
23 Installation Instructions
Table 8: Soft starter environmental specification
-10°C to +60°C
-30°C to +70°C
Indoors - free from corrosive gas, flammable
gas, oil mist, dust and dirt
1400 m above sea level.
0.02g²/Hz from 10 to 50Hz, reducing linearly
on a log-linear plot to 0.0001g²/Hz at 500Hz.
of X, Y, Z axes)
Measurement position 5 cm from the soft
inside the closed cabinet
De-rate above 50°C at 1.4% per °C
Ideally < 50% @ 50° to < 85% @20°C
For the installation at an altitude above 1400m
de-rate the rated current of the soft starter at
0.67% per 100 m
Road transport vibration only