Author: Howard Hopper, UL Solutions Regulatory Services Director
UL Solutions has withdrawn the second edition of UL 2755, the Outline of Investigation for Modular Data Centers, which was last updated July 18, 2018. This action was taken because the evaluation requirements are outdated, no longer adequately address current safety concerns, and do not align with current installation code requirements.
The first edition of the UL 2755 OOI was originally published in October 2011 and was intended to evaluate modular data centers that were composed primarily of IT servers and ancillary equipment. The requirements were designed to help code authorities determine compliance with requirements in the National Electrical Code® (NEC). The second edition of UL 2755 was published in 2018 with updates that addressed some IT equipment-related issues not included in the 2011 edition.
Since 2018, there have been significant advancements to data center infrastructure and the types of equipment deployed in these modular units, including advancements in power, energy and cooling technologies. This technological evolution requires additional protection systems and safety requirements to address the mitigation of current hazards, which has led to the development of updated installation code requirements and regulations to address these concerns.
According to Christopher Jensen, UL Solutions Regulatory Services Manager, “We have withdrawn the second edition of UL 2755 because its requirements, last updated in 2018, are now obsolete. They are out of alignment with current installation codes and standards, and do not adequately address safety concerns and code compliance for modern modular data centers.”
UL Solutions has developed requirements for investigating modern prefabricated modular data centers, which are currently included in the third edition of UL 2755, published in 2025. The new edition is intended to include a comprehensive set of safety requirements that reflect modern data center technologies and model code requirements.
The data center landscape is rapidly evolving. UL Solutions is working with industry stakeholders, including owner-operators, original equipment manufacturers (OEMs) and code authorities, to help our requirements reflect current technologies, hazards and installation codes and standards.
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