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Entry type: FAQ Entry ID: 109477525, Entry date: 06/16/2015

What must be taken into account for industrial controls when replacing a motor with an IE3 motor in an existing system?

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This FAQ describe what is to consider when replacing an older motor with efficiency classes (eff3, eff2, eff1, or IE1, IE2) with a high-efficiency motor of efficiency class IE3.


General motor replacement in an existing system

When replacing a motor in an existing system, the usual electrical and mechanical variables have to be checked.

In relation to the industrial controls, you must check that the selection and electrical dimensioning of the switching devices are also valid for the new motor. Please also read the information in the product manuals of the respective devices.

However, there is more to be taken into consideration when replacing an older motor with efficiency classes (eff3, eff2, eff1, or IE1, IE2) with a high-efficiency motor of efficiency class IE3.

What does IE3 mean?

IE3 motors have been mandatory for line operation in Europe since January 1, 2015. In the initial stage for the 7.5 – 375 kW output range, and in the second stage this will be extended to include outputs down to 0.75 kW in 2017.

From an electrical viewpoint, IE3 motors behave somewhat differently to less energy-saving

models.  These motors usually have higher starting currents than more inefficient motors. Above all the inrush currents when connecting to the line have also increased substantially. These new motor generations thus require increased making and breaking capacities in the switching devices. During normal operation, the operating currents are usually somewhat lower.


Optimization of the Siemens industrial controls

We have consequently optimized the new generation of SIRIUS industrial controls comprehensively for IE3 motors.

You can find additional information on this topic at www.siemens.com/ie3ready

or in the configuration manual for SIRIUS Industrial controls with IE3 motors

You will find in the configuration manual an overview of all our products that we recommend for use with IE3 motors. Many products have been extensively adapted to meet to the new challenges, but with some products the breadth of applications is limited and a more powerful version may have to be used. You will find an overview of the adapted devices and their product versions here:

What must be specially observed in the case of industrial controls when a motor of an earlier generation is replaced with an IE3 motor?

Due to the changed properties of the IE3 motors, the inrush current also comes into play as a dimensioning variable when replacing an older motor with an IE3 motor. This has to be considered during configuring to ensure that the industrial controls are suitable for use with the new motor. Since the inrush current of the motor is unfortunately not specified, a direct comparison cannot be made. The industrial controls recommended by Siemens for IE3 motors have already been correspondingly optimized on the basis of extensive analyses.

Thus, when replacing a motor with an IE3 motor, we generally recommend the use of the appropriately optimized industrial controls to retain optimal functionality and suitability for practical use.

IE3 motors have higher starting and inrush currents on average. However, there are also IE3 motors with starting and inrush currents that are comparable with those of the previous motor generations. These, of course, are also managed with switching devices that have not been adapted.

An important indicator for this is the starting current that provides an estimate of the suitability of the existing industrial control. The inrush current is also taken into account implicitly in this regard.

Based on comprehensive analyses of different motor technologies, and on our empirical knowledge, we can make the estimate given below of the starting current per performance class for which it is not absolutely necessary to replace the switching devices due to the inrush current. This means that up to this starting current, we assume that the inrush current is managed with the non-adapted devices and with the previous dimensioning. This assessment does not replace comparison of the available motor data with the data of the switching device. Instead, it only allows an estimate of the inrush current.

The table below shows these limit values of the starting current per performance class.

Power [kW]


0,75  1,11,5 2,2  45,5  7,511 15 18,5  2230  3745 

Maximum starting current [A]

 12 18 26 36 49 67 89 120 169 240 284 311 418 507 622


Power [kW]


55 7590 110132 160200 250315 355

Maximum starting current [A]

 756 102212091511 1866



2800 3333 4266 4622


The values stated in the table are an estimate based on analysis.

In the case of higher starting currents, we recommend that the affected industrial controls are also replaced with Siemens IE3-ready devices when replacing motors.


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