Standard for industrial control panel builders changing

UL 508 is being phased out and replaced by UL 60947-4, which is designed to harmonize international standards by UL, the Canadian Standards Association, and the International Electrotechnical Commission (IEC) in Europe.

By Tom Fowler August 20, 2015

There’s a transition underway regarding UL 508 of which customers and control panel builders should be aware: UL 508 will soon be phased out and replaced by UL 60947-4-1. This change is the result of more than 10 years of work by the UL, National Electrical Manufacturers Association (NEMA), and others. The purpose is to harmonize international standards from UL and its counterparts such as the Canadian Standards Association (CSA) and the International Electrotechnical Commission (IEC) in Europe.

The story starts some 15 or 20 years ago at a meeting where a number of manufacturers of industrial control panels made the point that it was time-consuming and difficult for them to test each of their products to the various standards from each region, including UL, CSA, IEC, and others in Asia and elsewhere. They made the point that it took longer to complete all the testing for their products than it did to develop and manufacturer them.

The UL representative at the meeting understood their predicament and vowed to try to harmonize the UL 508 standards with the latest IEC standards. And UL, with help from industry representatives, has been working on doing that for 10 years.

The UL 508 standard is more than 200 pages long and the committee went through the standard paragraph by paragraph to find differences between IEC and UL test protocols. The committee compared the protocols them to see what the differences were, determine whether both methods were acceptable, or if one was better than the other. The committee hoped to keep the best of both worlds in the revised standard, while ensuring safety was the primary goal.

The end result is a phase-in of a new series of standards, UL 60947-4. UL 60947-4-1 most closely resembles UL 508 and the phase-in plan for the standard is:

  • Prior to Jan. 26, 2012, products were evaluated to the UL 60947-4 unless the customer specifically requested it be evaluated using UL 508.
  • Between Jan. 26, 2012 and Jan. 26, 2017, new products are to be evaluated to UL 60947-4 only, but revisions to existing products may be evaluated using UL 508 if requested.
  • After Jan. 27, 2017, all products must meet UL 60947-4 specifications.

While a new standard is being implemented, there aren’t many dramatic changes between UL 508 and UL 60947-4-1. Here’s the official word from an FAQ that the UL put together on the transition:

This harmonization work was undertaken with the intent of creating standards that, while being based upon and adopting IEC requirements, would incorporate sufficient national differences to ease the transition from UL 508 to UL 60947-4-1. This goal has largely been accomplished in all cases. While the UL 508 and UL 60947 series standards do not look the same, when taking into account the national differences included in the harmonized standards, they are essentially technically identical.

The committee worked on harmonizing the UL and IEC standards, but there are intrinsic differences in voltages used around the world. In North America, for example, industrial voltages are 480 V at 60Hz while in Europe it’s 400 V at 50Hz. Those seemingly small differences are huge in terms of how someone tests products and qualifies them to a standard. Within those parameters, the committee worked on normalizing the standards so manufacturers should have an easier time testing their products against the various iterations.

For customers-including panel builders—it’s an education process. And this process consists of understanding the transition taking place and what it means when a builder sees a reference to UL 60947 when they were expecting UL 508. 

Schneider Electric 


– Tom Fowler, Staff Product Specialist, Schneider Electric. Edited by Chris Vavra, production editor, Control Engineering,

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