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Low and Medium Voltage Transformers Testing and Certification

We evaluate transformers to a broad range of U.S. and international standards, which enables your products to expand into a global marketplace.

A picture of many transformers placed side-by-side on the ground.


From 24 volts (V) to 69 kilovolts (kV), low and medium transformers are a critical part of many electrical systems that are used to increase or decrease the voltage in electric power applications.

Like other industrial equipment, many transformers can be evaluated as open type or enclosed. Open-type equipment is ultimately installed in an enclosure before being put into service, whereas enclosed transformers can be rated for indoor use or any National Electrical Manufacturers Association (NEMA) or International Protection (IP) rating requested. In addition, enclosed transformers can be certified for use in classified areas, e.g., hazardous locations.

Manufacturers needing a high temperature insulation system class (above Class A) are encouraged to use an adopted insulation system to avoid long-term aging testing. You may use UL’s iQ™ database to search for systems by using a variety of parameters.

Areas of expertise

Testing and certification services for low and medium voltage transformers include:

  • Ignition transformers
  • Instrument transformers – low voltage and medium voltage
  • Low-voltage dry type transformers, general purpose, industrial control, class 2 and class 3
  • Medium voltage transformers – dry type and liquid filled
  • Swimming pool and spa transformers
  • Energy efficiency per the U.S. Department of Energy


As alternative energy needs grow, the demand for low and medium voltage transformers also grows. We evaluate transformers to a broad range of U.S. and international standards, including International Electrotechnical Commission (IEC) 61558, IEC 60076 and IEC 61869 as well as Institute of Electrical and Electronics Engineers (IEEE) standards, such as the C57.12 and C57.13 series. We can also evaluate transformers for efficiency and K-factor ratings.

In addition, we have several categories for current transformers, with the newest being UL 2808, the Outline of Investigation for Energy Monitoring Current Transformers. These are listed and suitable for field installation into panelboards (load centers).

image of a power supply

Webinar: How to Navigate Recent Changes to Transformer and Power Supply System Standards, 3rd Edition of IEC 61558-1

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Webinar: Transformers – Global Market Access/ Efficiency per DOE and NRCan

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