Energy storage cabinet requirements for wall separation

The diagram shows that each ESS unit can have a maximum rating of 20 kWh, and if you're going to install two units, let's say outside on your wall, you need to have the appropriate spacing between those units and three-feet separation from doors and windows per NFPA 855 15.6.1.

Individual ESS units shall have a maximum stored energy of 20 kWh per NFPA Section 15.7. NFPA 855 clearly tells us each unit can be up to 20 kWh, but how much overall storage can you put in your installation? That depends on where you put it and is defined in Section 15.7.1 of NFPA 855.

In Section 15.5 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.

Therefore, if you install multiple storage units, you have to space them three feet apart unless the manufacturer has already done large-scale fire testing and can prove closer spacing will not cause fire to propagate between adjacent units.

When installing Powerwall 3 indoors, the room must be at least 5.25 x 5.25 x 8 ft (1.6 x 1.6 x 2.4 m) or an equivalent room volume per UL 9540 and UL 9540A. This is the minimum room size for any Powerwall 3 system, regardless of whether it includes multiple Powerwall 3 and/or Expansion units. Figure 1.

Systems in these locations are also limited to 40 kilowatt-hours (kWh) of storage capacity. In all other locations noted above, the size limit is 80 kWh. On the exterior walls of the home, it's important to note that systems cannot go within 3 feet of doors or windows leading directly into the home.