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OBC DIVISION B · PART 3 · SECTION 3.6 — SERVICE FACILITIES

What does the Ontario Building Code require for electrical vaults and transformer rooms?

Electrical equipment vaults must be built as fire-rated service rooms free of unrelated services and storage, coordinated with the Ontario Electrical Safety Code, which adds construction, ventilation, drainage, door and clearance requirements, particularly for oil-filled transformer vaults.

Code reference
Rooms and vaults containing electrical distribution equipment are regulated as service rooms requiring fire separations from the rest of the building, restricted to their intended use, and constructed consistently with electrical safety regulations. Oil-filled transformer vaults attract more stringent enclosure, containment, ventilation and access requirements under the Ontario Electrical Safety Code and utility standards.
OBC Division B, Subsection 3.6.2.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

Electrical rooms are a three-way coordination problem between the OBC, the Ontario Electrical Safety Code and the local utility (for example Hydro One or Toronto Hydro vault standards), and the strictest requirement governs. Nail down vault location, exterior access, ventilation paths, oil containment and door swing during schematic design, because moving a vault later disrupts structure and site grading. Common pitfalls include unrelated piping routed through electrical rooms and working clearances eroded by other trades.

Plain language

Rooms that house transformers and main electrical gear must be fire-rated, kept clear of storage and unrelated pipes, and built to both the building code and Ontario's electrical safety rules. Big oil-filled transformers get especially tough vault requirements.

Related questions

What fire separation is required for service rooms in Ontario?Where can fuel-fired appliances be located in a Part 3 building in Ontario?What are the requirements for vertical service spaces and shafts in Ontario?

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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.