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CAN/CSA E61558-2-2-03: Safety Requirements for Control Transformers and Power Supplies – A Technical Overview
Comprehensive guide to the Canadian adoption of IEC 61558-2-2 for control transformers and associated power supplies
Introduction
CAN/CSA E61558-2-2-03 is the Canadian adoption of the international standard IEC 61558-2-2, Safety of power transformers, power supplies, reactors and similar products – Part 2-2: Particular requirements and tests for control transformers and power supplies incorporating control transformers. Published by the Canadian Standards Association (CSA Group), this standard establishes essential safety requirements for control transformers with a rated supply voltage not exceeding 1 000 V a.c. and rated frequency not exceeding 500 Hz. It covers both standalone control transformers and power supply units that incorporate such transformers, including those intended for use in industrial, commercial, and residential control circuits.
This article provides a detailed technical review of the standard’s scope, principal technical requirements, implementation considerations, and compliance notes relevant to manufacturers, test laboratories, and certification bodies operating in Canada.
Scope of CAN/CSA E61558-2-2-03
The standard applies to:
- Single-phase and polyphase control transformers (separately wound, auto-transformer, or safety isolating types) that provide power to control devices such as relays, contactors, programmable controllers, and instrumentation.
- Power supply units that incorporate a control transformer as an integral part, with or without rectification, filtering, and regulation.
- Transformers and power supplies intended for installation in accordance with the Canadian Electrical Code, Part I (CSA C22.1).
Excluded from the scope are transformers covered by other parts of the IEC 61558 series (e.g., Part 2-1 for separating transformers, Part 2-4 for isolating transformers, etc.). The standard does not cover transformers for toys, medical devices, or explosive atmospheres unless specifically referenced.
Intended use: Control transformers governed by CAN/CSA E61558-2-2-03 are typically used in circuits that require a voltage different from the supply voltage to operate control devices. They are not intended to supply power to loads that draw current continuously at the transformer’s full rated output; intermittent or short-time rated operation is common.
Technical Requirements
Insulation and Dielectric Tests
The standard prescribes insulation coordination based on the transformer’s rated insulation voltage (Ui) and the overvoltage category of the installation. Conducted dielectric tests include:
- Power-frequency withstand voltage test between windings and between windings and core/screen.
- Impulse voltage test where the rated insulation voltage exceeds 500 V or for circuits connected to the mains.
- Clearances and creepage distances must comply with the relevant tables in IEC 61558-1 (the general part).
| Rated insulation voltage Ui (V) | Test voltage – power frequency (V) | Test voltage – impulse (1.2/50 μs) (kV) |
|---|---|---|
| ≤ 50 | 500 | — |
| > 50 and ≤ 130 | 1 500 | 2.5 |
| > 130 and ≤ 250 | 3 000 | 4.0 |
| > 250 and ≤ 500 | 4 000 | 6.0 |
| > 500 and ≤ 1 000 | 5 000 | 8.0 |
Table 1 – Dielectric test voltages for windings of control transformers (based on IEC 61558-1 tables)
Thermal Requirements and Temperature Rise
Under normal operating conditions, the temperature rise of windings, core, and external surfaces must not exceed limits defined by the insulation class. The standard mandates a thermal test at rated voltage and rated current for the specified duty cycle (continuous, intermittent, or short-time). Temperature limits are set to ensure a minimum 20-year lifetime of the insulation system. For example, Class B insulation (130 °C) typically allows a maximum temperature rise of 80 K by resistance method.
Overload protection: The standard requires that control transformers either incorporate inherent thermal protection (e.g., thermal cut-out) or be used with an external overcurrent protective device. The protective device must interrupt the circuit before the winding temperature exceeds the permissible limit under overload or short-circuit conditions.
Short-Circuit and Overload Performance
Control transformers must withstand a short-circuit of the secondary winding for a specified duration without exceeding permissible temperature limits or presenting a fire hazard. Two options are defined:
- Inherently short-circuit proof: The transformer’s design limits the short-circuit current so that no damage occurs.
- Non-inherently short-circuit proof: An external protective device (e.g., fuse or circuit breaker) is required. The standard specifies the maximum clearing time and let-through energy (I²t) that the transformer must withstand.
Protective Bonding and Earthing
Accessible conductive parts that could become hazardous live in the event of a basic insulation failure must be reliably connected to the protective earthing terminal. The bonding conductor must have a cross-sectional area at least equal to the largest size of the supply conductors, with a minimum of 1.5 mm² (copper). The resistance between the earthing terminal and any accessible metal part must not exceed 0.1 Ω.
Important: Failure to provide adequate protective bonding can create a shock hazard. All design verification tests must include a bonding impedance test per IEC 61558-1 Clause 18.2.
Implementation Highlights
Differences from IEC 61558-2-2 Base Standard
CAN/CSA E61558-2-2-03 is technically equivalent to IEC 61558-2-2:1998 with Amendment 1:2000, but incorporates national deviations to align with Canadian electrical codes and climatic conditions. Key differences include:
- Rated supply voltage range adjusted to match nominal Canadian voltages (e.g., 120 V, 208 V, 240 V, 480 V, 600 V).
- Ambient temperature range extended to –30 °C for indoor/outdoor use in Canadian climates.
- More stringent requirements for terminal markings, including explicit identification of neutral and line conductors.
- Wiring terminals must accept conductors sized according to Canadian Electrical Code Table allowances.
Design Considerations
When designing a control transformer for compliance with CAN/CSA E61558-2-2-03, engineers should consider:
- Insulation coordination based on rated impulse voltage for the overvoltage category (usually Category II or III).
- Use of UL/CSA recognized insulation materials to simplify final certification.
- Selection of thermal protective devices that are approved to CSA C22.2 No. 0 or relevant component standards.
- Provision for adequate ventilation, especially for enclosed power supply units.
Compliance tip: Many testing laboratories offer a combined IEC/CSA certification program, allowing a single design to be tested for both international and Canadian markets. Leveraging such programs can reduce time-to-market and duplication of effort.
Compliance Notes
To certify a product under CAN/CSA E61558-2-2-03, manufacturers must:
- Submit samples to a CSA-recognized testing laboratory (e.g., CSA Group, Intertek, UL) for type testing according to all normative clauses.
- Provide a technical file including: circuit diagrams, bill of materials for the insulation system, rated electrical parameters, and calculations for clearances/creepage distances.
- Ensure that the factory production line is subject to routine testing (dielectric strength, earthing continuity, and functional test).
- Mark the product with the relevant CSA certification mark or report number, along with ratings, caution statements, and the standard number.
Periodic surveillance audits may be required to maintain certification. The standard does not impose a specific recertification interval, but most certification bodies require annual factory inspections and occasional retesting.
Documentation Requirements
Each unit must be accompanied by instructions for installation, operation, and maintenance. The instructions must include:
- Rated voltage, frequency, and power.
- Type of protective device required (if not inherently short-circuit proof).
- Environment conditions (temperature, pollution degree).
- Connection diagrams.
Frequently Asked Questions
Q: Is CAN/CSA E61558-2-2-03 mandatory in Canada?
A: While adoption of CSA standards is generally voluntary, provincial and territorial electrical codes typically require compliance with CSA safety standards for electrical equipment. In practice, control transformers sold in Canada are expected to carry a recognized certification mark demonstrating compliance with this standard.
A: While adoption of CSA standards is generally voluntary, provincial and territorial electrical codes typically require compliance with CSA safety standards for electrical equipment. In practice, control transformers sold in Canada are expected to carry a recognized certification mark demonstrating compliance with this standard.
Q: Can a transformer certified to IEC 61558-2-2 be considered compliant with CAN/CSA E61558-2-2-03?
A: Only if the national deviations (Canadian) are also satisfied. Most certification bodies will accept an IEC test report as a basis but will require verification of the additional national requirements. It is advisable to request a combined IEC/CSA certification from the onset.
A: Only if the national deviations (Canadian) are also satisfied. Most certification bodies will accept an IEC test report as a basis but will require verification of the additional national requirements. It is advisable to request a combined IEC/CSA certification from the onset.
Q: What types of control transformers are covered by this standard?
A: The standard covers control transformers and power supplies incorporating a control transformer, where the output voltage is typically used to operate control devices such as relays, contactors, solenoids, and programmable logic controllers. Both single-phase and polyphase types are included.
A: The standard covers control transformers and power supplies incorporating a control transformer, where the output voltage is typically used to operate control devices such as relays, contactors, solenoids, and programmable logic controllers. Both single-phase and polyphase types are included.
Q: Does the standard address environmental performance (e.g., RoHS)?
A: No. CAN/CSA E61558-2-2-03 is solely a safety standard. Environmental requirements such as restrictions on hazardous substances are covered by separate regulations (e.g., Canada’s Prohibition of Certain Toxic Substances Regulations). However, material declarations may be requested during certification.
A: No. CAN/CSA E61558-2-2-03 is solely a safety standard. Environmental requirements such as restrictions on hazardous substances are covered by separate regulations (e.g., Canada’s Prohibition of Certain Toxic Substances Regulations). However, material declarations may be requested during certification.