Overview
EN 61643-351:2017 (identical to IEC 61643-351:2016) specifies performance requirements and test methods for surge isolation transformers (SITs) used in telecommunications and signalling networks. The standard defines test circuits and procedures to determine and verify SIT surge parameters and gives preferred performance values for key characteristics. SITs covered by this standard are intended for signal levels up to 400 V peak-to-peak and are designed to mitigate the onward propagation of common-mode voltage surges from lightning or other transient overvoltages. Note: SIT behaviour under differential‑mode lightning surge conditions is not covered.
Key topics and technical requirements
- Scope and service conditions: ambient temperature, humidity, altitude and microclimate classifications relevant for SIT performance and testing.
- Surge conditions and mitigation: definitions of common‑mode surge scenarios and how SITs reduce propagation of common‑mode transients.
- Characteristic measurements: procedures for measuring input-to-output winding capacitance and related electrical characteristics.
- Insulation and withstand tests: methods to measure insulation resistance and to verify the rated impulse withstand voltage of SIT windings (including construction and pass/fail templates for impulse tests).
- Signal performance: measurement of SIT voltage‑time product and signal handling up to specified peak‑to‑peak voltages.
- Ratings and thermal tests: rated winding DC current and winding conductor temperature rise test circuits.
- Identification and documentation: required datasheet information and marking for traceability and compliance.
Practical applications
- Protection of telecom and signalling links: SITs are specified to prevent common‑mode surge propagation into sensitive equipment in telecommunication exchanges, base stations, signalling cabinets and control networks.
- Component selection and design: manufacturers use the standard to design SITs that meet defined impulse withstand and leakage characteristics.
- Type testing and QA: test laboratories and certification bodies apply the specified test circuits and pass/fail criteria to verify product conformity.
- System integrators and specifiers: engineers writing procurement specs or integrating surge protection into networks rely on EN 61643-351 to ensure interoperability and adequate surge performance.
Who should use this standard
- SIT manufacturers and component designers
- Test houses and conformity assessment bodies
- Telecom equipment designers, installers and maintenance engineers
- Standards writers and procurement/specification teams
Related standards
- EN/IEC 61643 series (components for low‑voltage surge protective devices)
- Referenced IEC publications such as IEC 60060‑1 and environmental classification standards used for complementary test guidance (see normative references in EN 61643-351).
Keywords: Surge isolation transformers (SITs), EN 61643-351, IEC 61643-351, surge protective devices, common-mode surge, impulse withstand voltage, telecommunications, signalling networks.
