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Energy storage systems in residential occupancies – Code File, February 2022

February 24, 2022  By Nansy Hanna, P.Eng.



February 24, 2022 – As we continue moving toward net zero, the need for energy storage systems (ESSs) will continue to rise in both residential and non-residential applications. Unfortunately, some confusion has arisen around 2021 Canadian Electrical Code requirements for residential applications, so let’s examine the installation of an ESS in a dwelling unit.

The CE Code introduced two definitions for energy storage systems: Residential Use and Non-Residential Use. The former is marked as being suitable for residential use, and conforms to the requirements of ANSI/CAN/UL 9540 “Energy storage systems and equipment”.

Further, an Appendix B Note to Rule 64-918(1) clarifies that UL 9540 requires ESSs intended for dwelling units to be marked “Suitable for use in residential dwelling units where permitted”. (Non-Residential Use systems are defined as not marked as being suitable for residential use.)

These definitions introduce a restriction that seems to be based on UL 9540, but such a restriction is not actually intended by the standard. Moreover, as of today, there are no energy storage systems marked “Suitable for use in residential dwelling units where permitted” available on the market.

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In fact, the purpose of UL 9540’s marking of ESSs with “Suitable for use […]” is to permit units that have passed additional rigorous testing to be installed in the living or habitable areas of a dwelling unit (where permitted by the AHJ).

Rule 64-918(1) further prohibits ESSs with a storage capacity greater than 1 kWh or utilizing lithium-ion batteries from being installed in dwelling units. Period.

Meantime, UL 9540 allows certified ESSs that are not marked for residential use—but meet the regular tests in the standard—to be installed in non-living or non-habitable spaces of a dwelling unit (e.g. utility closets, attached garages or storage spaces). This is evident in Table E.1 “Residential use ESS” where it is further clarified by showing the capacity and separation requirements of ESSs permitted in dwelling units.

This restriction in the CE Code is also in contradiction of NFPA 855 “Installation of stationary energy storage systems”. Clause 15.6.1 permits ESSs to be installed in attached and detached garages; in enclosed utility closets, and storage spaces.

NFPA 855 further clarifies that when the room or space where the ESS is to be installed is not finished, the walls and ceiling shall be protected with not less than 5/8-in. Type X gypsum board. (Note: NFPA 855 requires ESSs to conform to UL 9540).

Subrule 64-918(2), which prohibits installing ESSs utilizing batteries below grade, is also raising questions because it is unclear whether this applies to dwelling units. If there is any consideration by an AHJ to permit ESSs in dwelling units, should they be permitted in basements? In a typical house, a utility room in a basement—or an unfinished basement—is a not habitable area.

Therefore, a basement could be a good location for an ESS. (Although other factors should be taken into consideration e.g. is the basement in a flood hazard area, is there a functional smoke detector, will there be a dedicated ESS storage room with at least 1-hour fire rating as per NFPA 855 intent).

Subrule 64-918(6) permits “Residential Use” ESSs to be installed in garages of dwelling units, provided any single ESS does not exceed 20 kWh storage capacity; multiple ESSs do not exceed 40 kWh capacity; and ESSs are spaced not less than 1 m apart.

Knowing that UL 9540’s intention for marking ESSs with “Suitable for use […]” is to permit these units in living or habitable areas of dwelling units, one wonders whether Subrule 64-918(6) actually intends to permit ESSs—approved to UL 9540—to be installed in the garage of a dwelling unit. That approach would align with NFPA 855.

It is important to review and understand the intent of these new rules, and consult your AHJ during the design phase for projects involving energy storage system installations in residential occupancies.

Meantime, the Section 64 Technical Subcommittee is working on a proposal to update ESS rules, with specific advice for residential applications. Visit CSA Group’s Public Review page and get involved.


Nansy Hanna, P.Eng., is senior director, Engineering & Regulations, at Ontario’s Electrical Safety Authority (ESA). She is also chair of the Canadian Advisory Council on Electrical Safety (CACES) and a member of the ULC Advisory Council, CSA Technical Committee on Industrial, Consumer and Commercial Products and CSA CE Code-Part I, Sections 24, 32, and 46. She can be reached at nansy.hanna@electricalsafety.on.ca.

This column—along with more great content—appears in the February 2022 edition of Electrical Business Magazine. Back issues are located in our Digital Archive.


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