Certifications for medium voltage VFDs
Introduction
Medium voltage variable frequency drives (MV VFD) play a crucial role in various industries by providing efficient and reliable control of motors, optimizing the technological processes and providing considerable energy savings.
The MV VFDs are installed globally, across different countries and continents. They serve in various industries and applications. Thus, various standards, regulations, laws and requirements apply. The manufacturers need to ensure compliance with those standards and requirements.
This post is dedicated to the topic of certifications of medium voltage VFDs. Note that the perspective provided here is the view of a European VFD manufacturer.
Why is certification required?
Certifications act as formal acceptance gates across safety, legal compliance, and commercial risk. From an insurance perspective, certified equipment reduces uncertainty and helps demonstrate due diligence; in the event of damage, fire, or injury, certification can significantly influence claim acceptance, liability allocation, and even premiums. Regulatory frameworks in many regions make certification mandatory for installation and energization, as authorities and inspectors may reject non-certified systems or require costly site evaluations. In parallel, customer specifications often impose certification as a contractual deliver-able to standardize risk management, simplify audits, and ensure global consistency across installations — even where local law does not explicitly require it. Finally, jurisdictional differences mean that approvals are not universally transferable: a drive accepted in one country or state may be rejected elsewhere due to local electrical codes, inspection practices, or sector-specific rules (e.g., marine or hazardous areas). Because certifications influence design choices, component selection, testing scope, documentation effort, and change management, they directly affect project cost, lead time, and com-missioning readiness—often as strongly as technical performance requirements. Misinterpretations in any of those directions, e.g. wrong certification choices, or engineering mistakes leading to delays, re-design usually coming with Late delivery fees or a complete system rejection by the customer. Hence it is important to know from the start of the project, which requirements are necessary to be handled.
As Europeans, we build according to IEC standards, which is why they are not specifically mentioned in this blogpost. It is widely used as base for UL and CSA harmonized standards.
What standards apply?
Europe based manufacturers use IEC standards as a base for design, manufacturing and testing of the equipment. Depending on the country of installation or specific industrial application, additional certification may be required.
If the final installation of the drive system is in a European country, then the IEC standards are typically expected and fully sufficient. Most countries in Asia follow IEC standards thus also there no additional certification is required. A different situation is when exporting the equipment to North America. United States may require certification according to UL while Canadian end users expect certification according to CSA standards.
From the industry specific certifications we will have a closer look at marine and the associated certification bodies.
IEC standard organization
Founded in 1906, the IEC (International Electrotechnical Commission) is the world’s leading organization for the preparation and publication of international standards for all electrical, electronic and related technologies. These are known collectively as “electrotechnology”.
Underwriters Laboratories (UL)
Underwriters Laboratories is a global safety science company. It is the largest and oldest independent testing laboratory in the United States, founded in 1894. UL offers its services in five strategic areas, from product safety, environment, life and health, university, and verification services.
Canadian Standards Association (CSA)
CSA Group is a global organization dedicated to safety, social good, and sustainability. CSA Group is a leader in standards Development and in Testing, Inspection and Certification around the world, including Canada, the U.S., Europe, and Asia. The mission of CSA Group’s not-for-profit Standards Development Organization is to enhance the lives of people through the advancement of standards in the public and private sectors.
How to get the UL or CSA certification?
There are basically two ways:
A) Full certification (entire production line is certified)
Product is designed and tested considering the standards (UL, CSA) from the beginning. The requirements are inherently fulfilled. The NRTL issues the certification. The VFD manufacturing site is periodically audited to ensure compliance.
This is a standard path for repeated quantity shipments into countries requiring such certification.
B) Spot approval / field certification
This path is suitable for low volume shipments (few units per year). UL, TÜV, Intertek, or another NRTL sends an engineer to the factory or installation site in the U.S. to inspect and test the specific unit. Approval applies only to that specific unit, not the product line.
Objectives and Scope
Below is a short, structured overview of the most relevant special certifications / approval frameworks for medium voltage variable frequency drives (MV VFD).
*AHJ, or Authority Having Jurisdiction, refers to the organization, office, or individual responsible for enforcing codes, standards, and safety regulations within a specific area. AHJs play a critical role in ensuring compliance with building codes, fire codes, and other safety regulations.
Certification vs. Compliance vs. Standard Conformity
Definitions
Certification refers to a formal confirmation by an independent, accredited third party, usually an inspector, that a product or system meets the requirements of a defined standard, typically based on testing, assessment, and sometimes ongoing surveillance. In the UL framework, a distinction is made between Listing and Recognition: UL Listing applies to complete end products that are evaluated for safe field installation and use, whereas UL Recognition applies to components or subassemblies that are assessed for use within listed equipment under specified conditions and are not generally intended for standalone installation. Marine Type Approval is an approval issued by a marine classification society confirming that equipment design and testing comply with marine rules and that the equipment is suitable for shipboard or offshore operation under harsh environmental and operational conditions. Finally, compliance or self-declaration, often used in the context of IEEE standards, indicates that the manufacturer or supplier claims conformity based on internal verification such as studies, calculations, and tests; this conformity is frequently contractual in nature and may not involve independent third-party certification.
Certification Ecosystem
The certification ecosystem describes the network of organizations that assess and approve products against safety and industry standards.
NRTL bodies (e.g., UL, Intertek/ETL, TÜV Rheinland) are accredited testing laboratories recognized in North America to certify electrical equipment for safe installation and acceptance by authorities having jurisdiction. Notified bodies are independent organizations designated by EU member states to perform conformity assessment under specific EU directives; in the context of ATEX, they evaluate and certify equipment intended for use in potentially explosive atmospheres. Classification societies (e.g., DNV, ABS, Lloyd’s Register, Bureau Veritas) are maritime authorities that establish technical rules and issue type approvals and certifications confirming that equipment is suitable for ship and offshore operation, particularly with respect to environmental robustness and vessel safety requirements.
Lifecycle implications
Certifying an MV VFD against a specific standard—while simultaneously incorporating additional customer-specific requirements—typically imposes a substantial impact on the project schedule compared with a standard execution approach. The certification path must therefore be de-fined already during the tender and design phase, requiring clear alignment between client, sales, and engineering on the drive’s functional scope, operating conditions, and the applicable certification framework. This early definition is essential because certification introduces incremental costs and lead-time drivers across all project phases, which must be quantified and contractually reflected at bid stage. During the engineering phase, component and material selection must comply with the target standard and approved component lists, which may differ significantly from established internal design practices and supply chains. In addition, certification requires an expanded and tightly controlled documentation package, subject to review by the involved third-party body for both spot checks and type approval audits. Crucially, late changes in material, component suppliers, or functional requirements can invalidate the certification basis and trigger partial or full re-certification, potentially shifting nonconformities to site commissioning, where remediation is considerably more costly and can lead to significant project delays.
Medium voltage VFDs: Relevant Architecture and Certification Drivers
Risk Factors Triggering Certifications
- Fire and electric shock hazard
- Insulation coordination
- EMC / harmonic distortion
- Hazardous location operation
- Shock/vibration (marine)
- Arc-flash and fault containment
UL Certification for Medium Voltage VFDs
UL Standards Typically Applied:
- UL 508A (industrial control panels)
- UL 61800-5-1 (adjustable speed drives safety)
- UL 50 / 50E (enclosures)
- UL 840 (creepage/clearance)
UL Listing vs Recognition
In UL certification for medium voltage VFD, the output depends strongly on the scope boundary (drive only vs. drive + auxiliaries) and on whether you are trying to certify a complete end product or parts of it. In practice, UL Listing of the full MV drive cabinet/system is achievable, but it is typically limited to standardized product variants and requires tight configuration control. UL Recognition is more common at the component/subassembly level (e.g., power modules, control boards, insulation systems), and it is often the more realistic pathway when the drive is custom-engineered, modular, or project-specific.
To achieve an UL Listing for a medium voltage VFD, it must be treated as a repeatable product with a stable design and defined configurations. It must be a complete package including cabinets, power conversion, control, protection and interfaces and use only defined options like cooling variants, input transformer options as certified variants, etc. The wiring and markings need to be according to the certification. Further, the manufacturer must be able to provide UL follow up services and the design needs to be evaluated against UL 61800-5-1.
The more common UL Recognition process allows the manufacturer and client to enlarge the offer of drive functions and material. Through evaluation of an inspector the following items must be recognized:
- insulation systems / spacers / barrier materials
- power semiconductors and modules (IGBT stacks)
- capacitors, reactors, transformers
- fuses, contactors, terminal blocks, wiring components
- PCB assemblies, control units
Design and Test Requirements
From a design perspective, the drive must demonstrate compliant insulation coordination, including adequate clearance and creepage distances, appropriate protective separation between hazardous voltages and accessible circuits, and robust protective bonding/earthing concepts. Construction as-pects such as enclosure, wiring, protection against access to live parts, and the use of suitably qualified/recognized components are also key evaluation elements. From a test perspective, typical qualifi-cation activities include dielectric withstand tests, verification of safe operation under defined fault scenarios, temperature rise and thermal performance assessment, and validation of protective func-tions and labeling/documentation requirements.
CSA certification for Medium Voltage VFDs
CSA Framework
- CSA C22.2 series
- CSA 22.2 No 274
- Relationship to IEC/UL and harmonization
Design and Test Requirements – Differences to UL
As CSA 22.2 No 274 and UL 61800-5-1 are largely harmonized today, most of the design and test requirements are very similar. However, there are still practical differences that matter in projects, mainly due to the CEC (Canadian Electrical Code) context, national deviations and how the certification body interpret and verify specific items. CSA itself states, that the IEC requirements were reviewed and accommodated “whenever possible”, i.e. harmonization is intentional but not complete. Regarding component and protective device details, CSA emphasizes specific areas that can trigger engineering re-work if missed and require detailed documentation.
Marine Certifications
In comparison to the above discussed, labelled certifications, marine certifications are typically type approvals aligning with the rules of classification Societies such as DNV, ABS, Lloyd’s Register, Bureau Veritas, Class NK and RINA, to name the most relevant Maritime Authorities. It is used to demonstrate suitability and reliability under maritime operating conditions, not only electrical safety. The certification focuses strongly on environmental and performance robustness, including validated resistance to vibration, humidity, salt mist and corrosion, temperature changes and EMC.
The role of Classification Societies and Type Approval
As in the prior mentioned certification processes it is important that already in the tender phase a per-son with the Societies topics knowledge is included in the project. Further they are involved in reviewing the plans, material and technical drawings, to ensure that the product design applies with the rules and standards of the Class Society.
The type approval is a certification process designed to certify mass-produced products. A lot of marine drives have to meet the same requirements, even when produced for different clients. To arrive at a type approval stage, the design of the drive has to be reviewed and the production audit has to be passed.
Implications for medium voltage VFDs
One of the main focuses for the marine standard societies lays in proving the robustness and resilience of electrical equipment against the harsh maritime environment, such as the capability to withstand salt water corrosion, the extreme temperature and rapid temperature changes and mechanical vibrations, without compromising its performance.
This enforces certain alternations on the medium voltage VFDs.
- cabinet structure
- cooling / corrosion protection
- conformal coating
- marine cable and gland selection
- fire integrity and segregation rules
Key Standards and Test Regimes
Each society develops their own standards (class rules), which are based on knowledge, research, indus-try experience and flag states and international maritime regulations. However, many of these standards are similar, which leads to the societies referencing each other.
Some examples of key standards are:
- DNV-GL: Guidelines for safety and reliability of marine power systems with the focus on robust-ness and resilience of the power system against the maritime environment
- DO-160: originally developed by the RTCA (Radio Technical Commission for Aeronautics), focus on environmental testing conditions
- ABS Rules for Building and Classing Marine Vessels: safety and performance requirements for AC and DC systems in marine applications
The standards and condition can vary slightly when another society is applicable.
Some examples of necessary tests:
- performance tests
- power supply fault tests: a Minimum of 3 interruptions in 5 Minutes with a switching-off time of 30s each case
- dry and damp heat (IEC 60068-2-2:2007 and IEC 60068-2-30:2005): 16 hours at 55°C or 70°C, for humid situations: 2 cycles à 12 hours at 55°C and 95% humidity
- vibration (IEC 60086-2-6:2007): depending on the test, the frequency varies from 2 to 100Hz during 90 minutes
- inclination (EC 60092-504:2016): inclined to an angle of min. 22.5° each side for a period of 10 seconds
- insulation resistance: Insulation tests need to be performed before and after the performance tests such as high voltage test or salt mist test, etc. and need to be executed between all phases and earth an where appropriate between the phases
- high voltage: the separate circuits need to be tested against each other and all circuits connected to each other need to be tested against earth
- cold (IEC 60068-2-1:2007): during 2 hours, a minimal temperature difference from -25°C to max. 5 °C has to be applied
- Salt mist (IEC 60068-2-52:2017): 4 spraying periods with a storage of 7 days each
- Electrostatic discharge (IEC 61000-4-2:2008): 10 pulses per polarity with 1 sec of time in between them
- Electromagnetic field (IEC 61000-4-3:2020): to simulate electromagnetic fields radiated by different transmitters
- Electrical fast transients/bursts (IEC 61000-4-4:2012): with a pulse rise time of 5ns, a pulse width of 50ns 2kV(power supply port/earth), 1kV (I/O, data), pulse period of 300ms, burst du-ration 15ms, duration of 5 minutes
- Flame retardant (IEC 60092-101:2018 or IEC 60695-11-5:2016): flame application is 5 times for 15s with an interval of 15s
Good to know
- There are two ways how to obtain UL or CSA certification of the variable frequency drive.
- Low voltage VFDs for the US market are typically UL listed as it is a high volume business
- Medium voltage VFDs may use the spot approval path, especially if the volume is small
- UL 61800‑5‑1 is harmonized with EN 61800‑5‑1 thus the certification is getting easier for European manufacturers
- You can use CSA as NRTL to certify the product for the installation in the US
- You can use UL as NRTL to certify the product for the installation in Canada
Acknowledgement
This article was mainly authored by Fiammetta Zanazzi. We would like to thank her for an interesting topic and such valuable contribution.
References
[1] UL recognized component marks – what code authorities need to know, https://code-authorities.ul.com/wp-content/uploads/2014/04/ul_RecognizedComponentMarks.pdf
[2] CSA C22.2 NO. 274:17, CSA group, https://www.csagroup.org/store/product/2425136
[3] OSHA’s Nationally Recognized Testing Laboratory (NRTL) Program, https://www.osha.gov/nationally-recognized-testing-laboratory-program
[4] Marine Equipment Certification: Type Approval and Compliance, Marinetegrity, December 2024, https://www.marinetegrity.com/marine-equipment-certification-type-approval-and-compliance/
[5] Type Approval Test Specifications, Lloyd’s Register, https://www.lr.org/en/knowledge/lloyds-register-rules/type-approval-test-specifications2/type-approval-test-specifications/
[6] Certifying Power Systems for Marine (DNV-GL), https://eureka.patsnap.com/article/certifying-power-systems-for-marine-dnv-gl-and-aviation-do-160-standards
[7] ABB Drives for Marine, Industry brochure, https://library.e.abb.com/public/2e7b508ea530471ac125785b00446c95/Marine%20brochure%20RevB_lowres.pdf
[8] Industry requirements (series), MB Drive Services, available online, https://mb-drive-services.com/category/industry-requirements/
Hungry to learn more?
Want to know more about variable frequency drives and drive systems? Purchase our premium subscription!
0 Comments