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CAN CSA C22.2 No. 60079-6-17: Protection by Liquid Immersion ‘o’ for Hazardous Locations
A comprehensive technical guide to the scope, technical requirements, and compliance aspects of the Canadian standard for explosion protection by oil immersion
Scope and Classification
CAN CSA C22.2 No. 60079-6-17 is the Canadian adoption of IEC 60079-6:2015, Equipment protection by liquid immersion “o”. It forms part of the CSA C22.2 series of standards under the authority of the Canadian Electrical Code (CE Code, CSA C22.1). This standard specifies requirements for the design, construction, testing, and marking of electrical equipment where the protection principle is based on immersion of arc-producing or sparking components in a protective liquid (typically oil or synthetic fluid). Equipment protected by this method is designated as Ex ‘o’ and is intended for use in explosive gas atmospheres classified as Zone 0, Zone 1, or Zone 2 in accordance with the CE Code.
The standard applies to apparatus such as transformers, switch gear, starting resistors, and similar devices where internal arcs or hot surfaces are rendered non-incendive by complete or partial immersion in a liquid that prevents contact between the ignition source and the surrounding explosive atmosphere. It covers both Group I (mining) and Group II (surface industry) applications, with specific variations for each group.
Tip: When classifying the intended location, refer to the latest edition of CSA C22.1 (the CE Code) Part 1, Annex JB, for Zone classification requirements. Always verify the explosion group (IIA, IIB, IIC) and temperature class (T1–T6) before selecting Ex ‘o’ equipment.
Technical Requirements
Liquid Characteristics and Fill Level
The immersion liquid must be non-conductive, have high flash point (typically ≥ 300°C), and must be chemically stable under normal and abnormal operating conditions. The standard mandates that the liquid level be maintained such that all sparking contacts, arc-producing parts, and live components are fully submerged under all specified operating conditions, including tilting up to 15° from the normal installation plane.
| Liquid Type | Flash Point (°C) | Kinematic Viscosity (cSt at 40°C) | Typical Application |
|---|---|---|---|
| Mineral Insulating Oil | ≥ 300 | 15–20 | Transformers, switchgear |
| Silicone Oil | ≥ 315 | 50–100 | High-temperature environments |
| Synthetic Ester | ≥ 300 | 25–35 | Environmentally sensitive areas |
Warning: Ex ‘o’ protection alone does not prevent internal ignition caused by sustained arcs or overheating. The equipment design must ensure that any arc within the liquid column does not breach the liquid surface or cause thermal decomposition of the liquid that could generate flammable gases.
Enclosure and Sealing Requirements
Enclosures for Ex ‘o’ equipment must be robust enough to retain the liquid under normal and abnormal service conditions. They must be provided with:
- Visible oil-level indicators (gauges) marked with minimum and maximum allowable levels.
- Pressure relief devices to prevent over-pressure due to internal faults.
- Drain plugs and sampling ports for periodic liquid analysis.
- Heat dissipation features (e.g., finned walls or external cooler) to keep liquid temperature within the approved T-class range.
Temperature and T-Class Compliance
The standard requires that under steady-state and transient conditions (including overload and locked-rotor scenarios), the liquid surface temperature and any external surface temperature do not exceed the limits of the assigned T-class. For example, T6 requires a maximum surface temperature of 85°C, while T1 allows up to 450°C. Temperature monitoring (e.g., thermostats) is generally required to disconnect the equipment if the liquid exceeds its safe operating range.
Compliance Note: A well-designed Ex ‘o’ assembly with correct liquid choice, proper level monitoring, and adequate cooling can achieve a high degree of reliability, making it a preferred solution for large electrical apparatus in Zone 1 and Zone 2 hazardous areas where maintenance access is limited.
Implementation Highlights
Installation Considerations
CAN CSA C22.2 No. 60079-6-17 does not cover installation requirements directly; those are addressed by the CE Code (C22.1) and CSA C22.2 No. 60079-14 (electrical installations in hazardous locations). However, equipment certified to this standard must be installed per its marking and documentation. Key installation aspects include:
- Ventilation: Adequate ventilation must be provided if flammable gases can accumulate above the liquid level due to leaks or maintenance.
- Foundations and Tilting: The equipment must be mounted rigidly and must not tilt beyond the certified angle (typically 15°) during operation.
- Ambient Temperature: The liquid selection and thermal design must account for the ambient temperature range expected at the installed site.
- Marking at Site: The equipment must bear the Ex ‘o’ marking along with the explosion group, temperature class, and the certification number. Additional marking for liquid type and level is also required.
Periodic Inspection and Maintenance
The standard (together with CSA C22.2 No. 60079-17 on inspection and maintenance) requires routine checks of liquid level, colour, dielectric strength, and the presence of sludge or carbon deposits. Any component that has operated under fault conditions must be inspected for liquid contamination and thermal damage.
Danger: Never operate Ex ‘o’ equipment if the liquid level is below the minimum mark. Exposure of energized arc-producing parts to the air space above the liquid can directly ignite an explosive atmosphere. Similarly, never bypass thermal protection or level switches.
Compliance and Certification Notes
Equipment designed to CAN CSA C22.2 No. 60079-6-17 must be certified by a recognized third-party certification body such as CSA Group, Underwriters Laboratories (UL), or Intertek (ITS) for use in Canada. The certification process includes:
- Review of technical documentation and drawings
- Type testing of a representative sample (including liquid compatibility, dielectric strength, thermal endurance, and flash tests)
- Production quality assessment or factory inspection
- Surveillance audits to maintain certification
The standard recognizes that deviations from the base IEC text (IEC 60079-6:2015) exist due to Canadian regulatory requirements, including differences in voltage and frequency ratings, ambient temperature ranges, and particular marking obligations under the CE Code. A detailed list of national deviations is provided in an annex of the standard.
| Marking Element | Example | Significance |
|---|---|---|
| Ex Marking | Ex ‘o’ IIB T4 Gb | Liquid immersion protection for gas environments (Group IIB, T4, equipment protection level Gb for Zone 1) |
| Liquid Designation | Mineral Oil (MO-300) | Specifies the approved liquid type and flash point |
| Ambient Range | –25°C to +40°C | Permissible operating ambient temperature |
| Certification Logo | CSA or cCSAus | Indicates certification by a Canadian-accredited body |
Key Takeaway: Compliance with CAN CSA C22.2 No. 60079-6-17 is essential for any Ex ‘o’ equipment placed on the Canadian market. By adhering to the technical requirements for liquid selection, enclosure design, temperature control, and marking, manufacturers can achieve both safety and market acceptance.
Frequently Asked Questions
Q: What is the difference between Ex ‘o’ and Ex ‘d’ (flameproof) protection?
A: Ex ‘d’ relies on containing an explosion within an enclosure that can withstand pressure and cool flame products, while Ex ‘o’ prevents ignition by immersing arcing components in a non-compressible liquid that quenches arcs and prevents gas ingress. Ex ‘o’ is especially suitable for large apparatus with high energy arcs (e.g., transformers) where flameproof casing would be impractically heavy.
A: Ex ‘d’ relies on containing an explosion within an enclosure that can withstand pressure and cool flame products, while Ex ‘o’ prevents ignition by immersing arcing components in a non-compressible liquid that quenches arcs and prevents gas ingress. Ex ‘o’ is especially suitable for large apparatus with high energy arcs (e.g., transformers) where flameproof casing would be impractically heavy.
Q: Can Ex ‘o’ equipment be used in Zone 0 (where explosive atmosphere is continuously present)?
A: No. In the Canadian framework, Ex ‘o’ EPL Gb is permitted only in Zone 1 and Zone 2. For Zone 0, protection types such as Ex ‘ia’ (intrinsic safety) or Ex ‘ma’ (encapsulation) are typically required. The standard does not include an EPL Ga rating for Ex ‘o’.
A: No. In the Canadian framework, Ex ‘o’ EPL Gb is permitted only in Zone 1 and Zone 2. For Zone 0, protection types such as Ex ‘ia’ (intrinsic safety) or Ex ‘ma’ (encapsulation) are typically required. The standard does not include an EPL Ga rating for Ex ‘o’.
Q: What maintenance is required for Ex ‘o’ equipment?
A: Routine maintenance includes checking the liquid level, verifying the dielectric strength of the liquid annually (or per manufacturer’s schedule), inspecting seals and gaskets for leaks, and testing thermal protection devices. Any change in liquid colour or odour may indicate contamination and warrants further investigation.
A: Routine maintenance includes checking the liquid level, verifying the dielectric strength of the liquid annually (or per manufacturer’s schedule), inspecting seals and gaskets for leaks, and testing thermal protection devices. Any change in liquid colour or odour may indicate contamination and warrants further investigation.
Q: Is the Canadian standard fully harmonized with U.S. requirements?
A: While CAN CSA C22.2 No. 60079-6-17 is derived from IEC 60079-6:2015, the U.S. typically references UL 698A (Industrial Control Equipment for Use in Hazardous Locations) or NFPA 70 Articles 500–504. The protection concept “liquid immersion” exists in the U.S. as a recognized protection technique, but the certification requirements and markings differ (Class/Division system vs. Zone system). Dual certification (cCSAus) is often obtained to cover both markets.
A: While CAN CSA C22.2 No. 60079-6-17 is derived from IEC 60079-6:2015, the U.S. typically references UL 698A (Industrial Control Equipment for Use in Hazardous Locations) or NFPA 70 Articles 500–504. The protection concept “liquid immersion” exists in the U.S. as a recognized protection technique, but the certification requirements and markings differ (Class/Division system vs. Zone system). Dual certification (cCSAus) is often obtained to cover both markets.