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Transformer overcurrent protection in Canada is governed by CEC Section 26, specifically Rule 26-252 for dry-type transformers and related rules for liquid-filled units. The CEC approach parallels NEC 450.3 but uses different maximum OCPD percentages and has slightly different conditions for primary-only versus primary-and-secondary protection.
CEC Rule 26-252 allows primary-only overcurrent protection when the primary OCPD does not exceed 250% of the rated primary current for transformers rated 9A or more (compared to NEC 450.3 Table which also uses 250% for this condition). For transformers with primary current less than 9A, the CEC allows the next larger standard OCPD above 125% of primary current.
When both primary and secondary overcurrent protection are provided, the CEC permits the primary OCPD to be as large as 300% of the primary rated current, with the secondary OCPD not exceeding 125% of the secondary rated current. The NEC 450.3 Table allows similar values (up to 300% primary with 125% secondary) for transformers 600V and below.
The key practical differences arise for Canadian transformers in industrial applications: the CEC Section 26 requirements for transformer vaults, clearances, and liquid containment differ from NEC Article 450. For Canadian permit submissions, citing Rule 26-252 (not NEC 450.3) is required.
The CEC also addresses distribution transformers (serving multiple secondary circuits) under separate provisions in Section 26. Coordinate protection requirements for distribution transformers require careful analysis under both the CEC and the utility interconnection agreement — a topic where Canadian and US practice diverge meaningfully because of different utility protection philosophies.
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Open CEC transformer ocpd calculator →Each Canadian province and territory has adopted a version of the CEC. Verify the adopted edition and local amendments with your AHJ.
CEC Rule 26-252 governs overcurrent protection for dry-type transformers. It specifies maximum primary OCPD percentages for primary-only and primary-plus-secondary protection configurations.
Under CEC Rule 26-252, the primary OCPD can be up to 250% of the rated primary current for primary-only protection (for transformers with primary current ≥ 9A). With secondary protection also provided, the primary OCPD can be up to 300% with the secondary OCPD at 125% of secondary rated current.
CEC Section 26 includes requirements for transformer installation locations, clearances, and — for liquid-filled transformers above certain ratings — vault or containment requirements. These requirements differ from NEC Article 450 and must be verified with the local Canadian AHJ.
Reference CEC Rule 26-252 (for dry-type transformers) and the adopted provincial edition (e.g., CEC 2021 per OESC in Ontario, CEC 2021 BC Electrical Safety Regulation). Always confirm the adopted edition with the local authority having jurisdiction.
Disclaimer: SparkShift calculators are provided for informational purposes. Always verify calculations against the adopted CEC edition in your province and confirm requirements with your local authority having jurisdiction (AHJ) before commencing work. The CEC edition adopted may differ by province — Ontario uses the OESC, BC uses the BC Electrical Safety Regulation, and other provinces have their own adopted editions.