How stringent is UL certification? What enabled ABB's relay protection series to secure this "North American certification mark"?

Colleagues working on North American projects have likely encountered this scenario: the technical specifications, drawings, and protection setting values are all in order, yet the client or the supervising engineer will ultimately ask one more question— "Has this batch of relay protection devices passed UL certification?"

This seemingly trivial question can often determine whether a project can proceed smoothly. In the engineering contexts of the United States and Canada, the UL mark is not an additional advantage, but rather a "entry threshold" in many scenarios.

This article gets straight to the point and addresses three key issues: what UL certification actually entails, how stringent its requirements are, and why ABB's Relion relay protection series has earned this certification and gained long-term market recognition.

01 The UL mark is not a "quality inspection report," but rather a third-party safety endorsement.

UL, short for Underwriters Laboratories, is a U.S.-based laboratory founded in 1894. It neither manufactures products nor acts as a quality inspector; its core business is to conduct independent testing and certification of products in accordance with safety standards.

Note that, strictly speaking, UL certification is not a "quality certification," but rather a "safety certification." It focuses on the three primary risks associated with a product in real-world use: fire, electric shock, and mechanical injury. The UL mark indicates that the product has been tested by an independent third party, confirming that it complies with the applicable standards regarding these specific risks.

One point that is easily misunderstood: UL does not equate to "better performance" or "enhanced functionality." Rather, it certifies "compliance with safety standards," not "superior technical specifications." Only by grasping this point can one truly appreciate UL's real value—it serves as the common language of "safety" within the North American market.

02 The rigor of UL certification: it is about "continuity," not "one-time compliance."

Many certifications are one-off endeavors: once the testing is complete and the certification is issued, little to no follow-up is typically required. UL, however, differs; its rigor is reflected in a complete and continuous process.

The general workflow is as follows:

Step 1: Product classification. UL classifies the product into its corresponding Category of Construction (CCN) and determines which safety standards apply—selecting the wrong standard can render all subsequent steps futile.

Step 2: Sample Testing. Engineers conduct a comprehensive suite of tests on representative samples in accordance with the standards, covering electrical, mechanical, material, and thermal performance aspects.

Step 3: Notice of Closure (NOC). Upon successful completion of the test, UL will issue a Notice of Closure.

Step 4: Initial production inspection. Simply completing the testing does not mean the product can be sold; UL will also dispatch personnel to conduct an initial production inspection at the factory to verify that mass production capabilities align with those demonstrated in the test samples.

Step 5: Authorize mass production (NOA). Once approved, mass production shall be authorized.

The sixth step—also the most challenging and the one that best demonstrates the true value of UL certification—is follow-up inspection (Follow-Up Services). Certification is not the end goal; UL conducts periodic spot checks on manufacturing facilities to continuously verify that products consistently comply with the standards. Should any deviation be detected, the certification may be suspended or even revoked.

Thus, the rigor of UL certification does not stem from the difficulty of any single test, but rather from its approach of transforming "certification" into a continuous compliance trajectory rather than a final endpoint. This poses a long-term challenge to manufacturers' capabilities in research and development, supply chain management, and production line consistency management.

03 What does it mean when a product obtains UL certification?

Market access in North America: In the United States and Canada, a vast array of regulations and engineering codes—many of which are enforced by AHJs (Authorized Inspection Agencies)—treat the UL mark as standard evidence of product compliance; consequently, many projects explicitly require the UL mark during bidding or acceptance processes.

Third-party trust endorsement. Having existed for over a century, UL enjoys widespread global recognition. Displaying the UL mark effectively communicates to both customers and regulatory authorities: "The safety of this product is overseen by an independent third party."

Continuous compliance assurance. Thanks to ongoing follow-up inspections, the UL mark is more than just a sticker—it represents an active supervisory mechanism in place.

A key advantage for overseas projects: although UL operates within the North American framework, its recognition has long been globalized. When domestic manufacturers expand abroad or overseas project owners conduct factory audits, the UL mark often serves as a trusted credential for rapidly establishing credibility.

04 ABB relay protection series: these models have already obtained UL certification.

ABB has already obtained the UL certification series.

ABB's Relion relay protection, control, and monitoring device series (615/620/640 series) already includes a number of models covered by UL certification, encompassing protection for feeders, transformers, motors, line differential protection, voltage protection, generator protection, as well as supporting human-machine interfaces (HMI), I/O modules, and power supply modules.

The main models include:

Protection and Measurement/Control: REF615 (feeder), RET615 (transformer), REM615 (motor), RED615 (line differential), REV615, REU615 (voltage), REG615 (generator), REC615/REX615 series, REX610, REX640A, REX640B, etc.

Supporting modules: HMI display unit, AOM4/DOM4 analog/digital I/O, PSMH/PSML power modules, RTD4, SSC600 substation controller, etc.

This means that these models can now be deployed in North American standard engineering environments in compliance with regulatory requirements, providing direct support for overseas expansion initiatives and Chinese enterprises undertaking projects—such as data centers, industrial power distribution, and new energy initiatives—within North America.

05 What enables ABB to secure this award and gain long-term recognition?

Obtaining UL certification is one thing; maintaining market recognition thereafter is another. ABB relies on several concrete strengths:

First is the standardized gene. From its inception, the Relion series has been designed to be compatible with both IEC and ANSI standard systems, enabling seamless integration with North American power grid engineering nomenclature, wiring practices, and protection logic—rather than relying on "ad-hoc adaptation."

The second key advantage is its digital capabilities. The Relion 615 series natively supports IEC 61850 (Edition 1/2), including GOOSE, PRP/HSR redundancy, IEC 61850-9-2 LE sampling values, and IEEE 1588 V2 time synchronization. In the context of the growing emphasis on intelligence and digitalization in North America, these features represent a critical competitive advantage.

The third aspect is reliability engineering. This includes the design of detachable and insertable units, standardized configuration, and stringent factory and type testing; from design through to mass production, "consistency" is treated as the fundamental baseline—a approach that precisely aligns with UL's subsequent follow-up inspection requirements.

Fourth is the quality and testing framework of its global operations. With decades of expertise in protection and control, ABB possesses testing and certification resources across the globe, enabling it to integrate certification requirements into the R&D phase—rather than waiting until testing is complete before making necessary adjustments.

In short: UL certification tests the product itself; sustained recognition, in turn, tests the entire system encompassing research and development, manufacturing, and quality management. ABB has precisely aligned itself with this trajectory, thereby building a robust foundation.

Final Remarks

Returning to the opening statement: when evaluating whether a relay protection product can be confidently introduced to the North American market in the future, one should no longer rely solely on marketing claims, but instead consider three key factors: which models are covered by its certifications, which standard framework was used for testing, and whether there is ongoing factory supervision following certification.

UL is your passport to safety and compliance; if your project requires both UL certification and relay protection, you've come to the right place.