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If you’re familiar with power conversion equipment, you may be familiar with the fact that there always seems to be more than one certification depending on the geographical location.

In North America, we have UL 508C,  the standard for ‘Safety for Industrial Control Equipment’ which covers industrial control and related devices rated 1500 volts or less used for starting, stopping, regulating, controlling, or protecting electric motors.

Meanwhile, in Europe, the standards for adjustable speed DC drive systems, power conversion equipment, control equipment, and motors is regulated by the International Electrotechnical Commission (IEC).

Starting in 2010, a consolidation effort was put into effect to harmonize these certifications into a new singular rating: UL 61800-5-1. While being based upon and adopting IEC requirements, this new rating incorporates national differences that would address U.S. installation requirements (NFPA 70, US National Electrical Code).

So what does this mean moving forward?

Starting back in February 2016, UL 61800-5-1 became the exclusive rating used for evaluation of new products unless specific requests are made by the manufacturer.


New products are defined as:

  • Any model or models that belong to a new series of drives (not previously Listed or Recognized to UL 508C)
  • Any new model to an existing series (currently Listed or Recognized to UL 508C) that requires an associated change to the ratings or construction details section of the Certification report for that series

As of February 1st, 2020, UL 508C will be withdrawn.

Existing certifications to UL 508C will be allowed to continue to be certified to the requirements in effect for the product provided there are no changes to the design after the implementation date. For example, if changes to the design, ratings, or the use of alternate components requiring a certification decision are submitted after the implementation date, the device (in its entirety) will need to be evaluated to the new requirements of UL 61800-5-1.

After February 1st, 2020, only UL 61800-5-1 will be used for drive investigations.

What’s different between UL508C and UL 61800-5-1?

Clearance and Creepage Requirements

  • UL 840 is no longer a standard referenced as a standard for investigating clearances and creepages.
  • Where protective separation is required, clearance and creepage requirements are greater than those required by UL 840 and UL 508C Tables 36.1 (columns B, C, and D), 36.3, and 36.4.
  • Surge protective devices cannot be used to reduce the overvoltage category (and thus the required clearance) for protective separation. When reducing the overvoltage category where basic insulation is required, the SPD’s are required to be monitored and an indication of their status provided. UL 840 did not require surge protective devices to be monitored with a fault status indication to reduce clearance requirements and also allowed surge protective devices to reduce the required clearances between any considered circuits/parts.
  • Impulse test for reduced clearances is not allowed where protective separation is required and only allowed for basic and functional insulation if a homogeneous electrical field is present. UL 840 allowed for impulse test in lieu of clearances in any construction.
  • Investigation of clearances and creepages is required on inner layers of PWB’s. Alternatively, the inner layers can be investigated to solid insulation requirements. UL 508C waived requirements on inner layers of PWB’s.
  • Note – where functional insulation is required the required clearances may be smaller

Short Circuit Test

  • All power outputs must be short circuit tested. UL 508C only required the motor output to be short circuit tested.
  • Note – Cotton indicator is required for all short circuit tests. UL 508C allowed for cotton to not be used when conducting the tests with circuit breakers.
  • Note – Voltages of secondary circuits must be monitored and not exceed certain levels during the short circuit and breakdown of components tests, or the AC/DC voltage test must be conducted after the short circuit test. This was not part of UL 508C pass/fail criteria.

Breakdown of Components Test

  • The circuit used for the breakdown of components test must be capable of standard and high fault currents based on manufacturer’s short circuit current rating; unless detailed analysis shows a different value is equivalent or more severe. UL 508C was not specific on the test circuit required for the breakdown of components test.
  • Note – Voltages of secondary circuits must be monitored and not exceed certain levels during the breakdown of components tests, or the AC/DC voltage test must be conducted after the breakdown of component test. This was not part of UL 508C pass/fail criteria.
  • Note – Required branch circuit protection and other test set-up requirements are specified. These are the same as the short circuit test. UL 508C did not have test set-up specifics.

Bonding Test

  • Products with accessible conductive parts are required to comply with the protective bonding test. UL 508C did not require a test for bonding of accessible conductive parts.
  • Note – Kits provided for bonding of multiple conduit entries in polymeric enclosures require a “CAUTION” marking. UL 508C did not require a “CAUTION” marking for bonding kits.

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