5 of NFPA 855, we learn that individual ESS units shall be separated from each other by a minimum of three feet, unless smaller separation distances are documented to be adequate and approved by the authority having jurisdiction (AHJ) based on large-scale fire testing. According to UL 9540 the separation between batteries should e 3ft (91. UL 9540 also provides that equipment evaluated to UL 9540A with a written report from a nationally recognized testing laboratory (NRTL), such as ETL, can be permitted to be installed with less than 3ft. NFPA 855 sets the rules in residential settings for each energy storage unit—how many kWh you can have per unit and the spacing requirements between those units. Accessibility and. The minimum spacing between energy storage cabinets is often dictated by several factors, including the manufacturer"s specifications, local building codes, and industry. In particular, spacing requirements and limitations for energy storage systems (ESS).