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Department for Business, Energy and Industrial Strategy

Converter-Fed Motors

1.1    Scope

Converter-fed motors are applied throughout industry and commerce in a wide range of ‘general purpose’ and specialist applications.

A converter-fed motor is designed to be operated from a non-sinusoidal multi-phase electrical power supply and may comprise permanent magnet, synchronous reluctance or other design.

A converter-fed motor drive is a combination of a motor and an electronic variable speed drive (VSD). The VSD can either be physically mounted on the motor to form a single factory assembled, integrated unit, or the VSD and motor can be supplied as a package of two units that are designed to be connected together during installation.

Converter-fed motors are available in a wide range of designs and efficiencies. The Energy Technology List (ETL) aims to support the purchase of higher efficiency products with rated power outputs ranging between 0.12 kW and 1,000 kW.

The ETL covers three categories of converter-fed motors:

  1. Converter-fed ac motors (sold without VSD).
  2. Integrated converter-fed motor drive units.
  3. Matched converter-fed motor drive packages.

Integrated converter-fed motor drive units include electrically commutated motors which comprise a brushless dc multi-phase motor and an integral electronic control device. The ac power supply is commutated to dc by the control device and the power output is used to rotate the motor.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.2    Definitions

Converter-fed motors are products that are specifically designed to convert electrical power into mechanical power, and to rotate a drive shaft at a speed that is directly related to the non- sinusoidal multi-phase electrical power supplied to the motor.

Converter-fed ac motor drives consist of a motor, and a matched, electronic, VSD that is specifically designed to provide the multi-phase electrical power input needed to operate the motor, and to vary its speed in a controlled manner in response to an external signal. 

1.3    Requirements 

1.3.1    Eligibility requirements  

Eligible products shall:

  • Be designed to include or operate with an electronic VSD
  • Incorporate a converter-fed motor that:
    a)    Has a rated operating voltage between 200 and 700 Volts
    b)    Has an appropriate Conformity Assessment mark.
  • Not incorporate any type of mechanical apparatus that derives its motive force from the product’s motor, except for fans or pumps incorporated solely for the purpose of product cooling or lubrication, integrated torque couplings, and position encoding mechanisms.
  • Not include a mechanically commutated dc motor

Category 1 (converter-fed ac motor) products shall be designed to operate with an electronic VSD providing a non-sinusoidal multi-phase ac electrical power supply to the motor.

Category 2 and 3 (converter-fed motor drive unit and package) products shall be configured for direct connection to the UK public electricity supply system, or a private alternating current supply of nominally fixed frequency and voltage. The electronic VSD should provide a non-sinusoidal multi-phase electrical power supply to the motor.

In addition, for all products (except for electronically commutated motors) that include an electronic VSD, the VSD shall also comply with the separate ETL criteria for Variable Speed Drives. 

1.3.2    Performance requirements 

Products shall have an efficiency at 100% of their maximum continuous speed rating that is greater than or equal to the values shown in Table 1.1 below, which vary with power rating and maximum continuous speed rating. If the product’s specific power rating is not shown in Table 1.1, then the performance threshold for the next highest power rating should be used to determine eligibility. 

Table 1.1    Performance thresholds for converter-fed motors and motor drive units

Rated Power of motor, PN (kW)

Efficiency at full load of motor and VSD combined (%)

2 Pole

4 Pole

6 Pole

8 Pole


>= 60.8

>= 64.8

>= 57.7

>= 50.7


>= 65.9

>= 69.9

>= 63.9

>= 58.7


>= 67.2

>= 71.1

>= 65.4

>= 60.6


>= 69.7

>= 73.5

>= 68.6

>= 64.1


>= 73.8

>= 77.3

>= 73.5

>= 69.3


>= 74.6

>= 78.0

>= 74.4

>= 70.1


>= 77.8

>= 80.8

>= 77.2

>= 73.0



>= 78.9

>= 82.5

>= 80.7



>= 81.0

>= 84.1

>= 82.7



>= 82.5

>= 85.3

>= 84.2



>= 84.3

>= 86.7

>= 85.9



>= 85.6

>= 87.7

>= 87.1



>= 86.8

>= 88.6

>= 88.1



>= 88.0

>= 89.6

>= 89.2

















































































315 up to 1,000





">=" means "greater than or equal to"
 "<=" means "less than or equal to"

Where the rated power (PN) is that of the motor, for ‘Duty type S1 – Continuous running duty’ as defined in Section 4.2.1 of BS EN 60034-1: 2010 “Rotating electrical machines – Part 1: Rating and performance”, and is determined with the product operating at 100 % of its maximum continuous speed rating.

The efficiency at full load refers to the overall efficiency of the motor and VSD combined.

1.4    Measurement and calculations

1.4.1    Measurement Standards and Test Requirements 

Product efficiency at 100% of maximum continuous speed rating shall be determined using either option a) or b) below:

  1. Type tests according clause 7.3 of BS EN 61800-9-2:2017 “Adjustable speed electrical power drive systems. Ecodesign for power drive systems, motor starters, power electronics and their driven applications. Energy efficiency indicators for power drive systems and motor starters.”

    Note: until further notice, results of tests according to BS EN 50598-2:2014+A1:2016 will also be accepted
  2. Method 2-1-2A according to Table 4 in Section 7 of BS EN 60034-2-1:2014 “Rotating electrical machines – Part 2-1: Standard methods for determining losses and efficiency from tests (excluding machines for traction vehicles)”. Where the input power P 1, shall be measured at the main input terminals to the electronic VSD.

Until further notice, products listed before September 2020 will be accepted with testing performed according to BS EN 60034-2-1:2007. 

Products shall be operated from a standard 230, 400 or 690 Volt ac, 50Hz electrical power supply during testing, and any filters that are required by the product in order to comply with The Electromagnetic Compatibility Regulations 2016 shall be fitted.

Where the product does not include a VSD, it may be tested using any appropriately matched VSD. If a single product is submitted for assessment, one detailed test report should be submitted.

For a product range, test results may be submitted in summary form provided:

  • Sufficient data is included to confirm that product performance was determined in accordance with the procedures and test conditions laid down in the relevant standards.

1.4.2    Rounding  

For the avoidance of doubt test data should be presented to 1 decimal place. As an example, a 4 pole, converter-fed motor with rated power output of 45.0kW and an efficiency at full load of 95.3% would be deemed to be a fail.

1.5    Verification for ETL Listing 

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing
  • Representative testing (see clause 1.5.1)

Further information regarding the first four routes can be found in Guidance Note 5 on the ETL product testing framework1

1.5.1    Representative testing

Where applications are being made for two or more products that are variants of the same basic design, test data may be submitted for a representative selection of models, provided that:

  • All variants are of the same product range as the representative models and the primary variations between models are rated power and physical dimensions.
  • All variants are constructed from the same materials.
  • At least one detailed representative test report is provided for each product range.
  • Clear descriptions of the formulae or mathematical model used for calculating performance of the variants, and details of measurements taken to verify this model are provided. Tests undertaken to verify the accuracy of the model shall be carried out in accordance with the test procedures described above.

It should be noted that:

  • The efficiency value stated on the ETL for tested products should be taken from the test data provided, and not from the calculated or modelled values.
  • If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
  • If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.  

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

1.7    Review 

1.7.1    Indicative review date 

The next technical review is scheduled for 2023-24. 

1.7.2    Illustrative future direction of the requirements  

Future changes to the specification may include:

A revision of the converter losses allowed for in the efficiency thresholds, to align with the findings from the Global Round Robin test programme for converter losses, which will inform IEC 61800-9-2. This is being performed from 2017-2021 by the EMSA and IEC SC 22G WG18.