UL · Underwriters Laboratories
The safety-certification body whose listing makes equipment routinely acceptable to code officials and insurers; unlisted gear waits, however good its engineering case.
Current numbers
NEC 2029 (code); UL listing pending800 VDC code and listing timeline: full code support targets NEC 2029, and no data-center SST had completed UL certification as of May 2026 (SemiAnalysis)
UL 9540A, 6th edition (published March 2026)UL 9540A sixth edition, published March 13, 2026; vent-gas ignition and large-scale fire testing
UL 1449 5th Ed.current North American SPD listing basis, ANSI-approved 2025; NEC mandates UL 1449 listing