Overview - IEC 62848-2:2019 (Voltage Limiting Devices)
IEC 62848-2:2019 is the International Electrotechnical Commission standard that defines Voltage Limiting Devices (VLDs) for DC traction systems. The standard specifies how VLDs must operate to meet protective provisions against electric shock from DC and combined AC–DC voltages in accordance with the IEC 62128 series, while taking stray current considerations into account. VLDs covered by this standard are intended to connect the track return circuit to the earthing system or to conductive parts within the overhead contact line or current collector zones to limit dangerous voltages.
Key topics and technical requirements
The standard addresses practical design, testing and performance requirements for VLDs used in railway DC systems, including:
- Classes of VLDs (classification and intended use: e.g., welding-shut spark gap, thyristor, mechanical switching, combined types)
- Characteristics and requirements
- Marking and identification
- Service conditions: normal outdoor/indoor and abnormal environments
- Electrical characteristics and thermal rating
- Response time and minimum performance criteria
- Protection against lightning and stray current effects
- Command and control features (for certain classes): local control, remote signalling, operation and alarm recordings
- Type and routine tests required for certification and quality assurance:
- Nominal triggering and non-triggering voltages
- Leakage current, DC current withstand, short-time withstand
- Response time tests for DC and combined AC–DC voltages
- Lightning and high-current impulse withstand
- Recovery voltage and reverse voltage tests
- Dielectric, degree-of-protection (IP), and environmental tests for outdoor equipment
- Determination of minimum current for safe short-circuiting (Class 1)
- Annex with preferred ranges of key parameters (nominal triggering voltage, rated current, impulse withstand, etc.)
Practical applications
IEC 62848-2:2019 is applied where limiting dangerous potentials on DC traction systems is required:
- Protection of track personnel and passengers by ensuring safe touch / step voltages
- Safety interfaces between the rail return and earthing systems in substations, depots and on-track equipment
- Design and selection of VLD components in overhead contact line zones and current collector zones
- Specification for procurement, factory testing and on-site acceptance of VLDs
Who should use this standard
- Railway electrical engineers and designers specifying protection systems for DC traction
- Manufacturers of voltage limiting devices and DC surge protection equipment
- Test laboratories and conformity assessment bodies performing type/routine tests
- Infrastructure owners, system integrators, and maintenance teams responsible for earthing and stray current mitigation
- Safety assessors and regulatory authorities referencing IEC 62128 and related railway safety standards
Related standards
- IEC 62848-1:2016 - Railway applications: DC surge arresters (metal-oxide surge arresters without gaps)
- IEC 62128 series - Electrical safety, earthing and the return circuit (protective provisions)
- IEC 60060‑1, IEC 62497‑1, IEC 62498‑2 and other normative references cited for test methods and environmental requirements
Keywords: IEC 62848-2:2019, voltage limiting devices, VLDs, DC traction systems, railway safety, surge arresters, IEC 62128, earthing, stray current, response time, type tests.