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IEC 62135-1:2015 โ Resistance Welding Equipment โ Safety Requirements for Design, Manufacture and Installation
📋 Introduction and Scope
IEC 62135-1:2015 specifies safety requirements for the design, manufacture, and installation of resistance welding equipment. This includes spot welding machines, seam welders, projection welders, butt welders, and flash welders, as well as their associated tooling and control systems. The standard covers equipment rated for all power levels, from small bench-top units used in jewelry manufacturing to large automotive production lines with hundreds of kVA of welding capacity.
This second edition (2015) significantly expanded upon the first edition (2004) by incorporating modern safety philosophies including risk assessment methodology aligned with ISO 12100, updated requirements for electrical safety reflecting IEC 60204-1 evolution, and new provisions for high-frequency inverters which had become dominant in the industry since the earlier edition.
💡 Engineering Insight
Resistance welding occupies a unique position in the machinery safety landscape because the welding current path passes through the workpiece (typically a human operator’s hands may be near the welding tips). This means the standard must simultaneously address the safety of the machine itself, the safety of the operator in close proximity to high currents, and the quality of the weld being produced — all of which are interdependent.
Resistance welding occupies a unique position in the machinery safety landscape because the welding current path passes through the workpiece (typically a human operator’s hands may be near the welding tips). This means the standard must simultaneously address the safety of the machine itself, the safety of the operator in close proximity to high currents, and the quality of the weld being produced — all of which are interdependent.
⚡ Electrical Safety Requirements
The electrical safety provisions of IEC 62135-1 are among the most critical, given the high currents (tens to hundreds of kA) and low voltages (typically 2–20 V at the secondary) involved in resistance welding:
| Safety Aspect | Requirement | Engineering Implementation |
|---|---|---|
| Protection against direct contact | IP2X minimum for live parts | Enclosures with tool-removable covers, interlocks on access panels |
| Welding circuit isolation | Transformer isolation between supply and welding circuit | Double/reinforced insulation, or protective screening |
| Protective bonding | All exposed conductive parts connected to PE | Bonding conductor cross-section ≥ 50% of supply phase conductor |
| Disconnection from supply | Visible disconnect or lockable isolator | Main switch with padlock provision, per IEC 60204-1 |
| Overcurrent protection | Protection against short circuit and overload | Circuit breakers or fuses sized for the welding transformer inrush |
| Residual current protection | RCD required for portable welding equipment | Type A or Type B RCD (sensitive to DC components) |
⚠️ Critical Consideration — Secondary Circuit Hazards
One unique aspect of resistance welding equipment is that the secondary welding circuit operates at very low voltage (typically < 20 V) but extremely high current (up to 100 kA). While the low voltage means there is no electric shock hazard from the secondary circuit under dry conditions, there is a significant burn hazard from incandescent weld splatter and a magnetic field hazard requiring special attention for operators with active medical implants (pacemakers, insulin pumps).
One unique aspect of resistance welding equipment is that the secondary welding circuit operates at very low voltage (typically < 20 V) but extremely high current (up to 100 kA). While the low voltage means there is no electric shock hazard from the secondary circuit under dry conditions, there is a significant burn hazard from incandescent weld splatter and a magnetic field hazard requiring special attention for operators with active medical implants (pacemakers, insulin pumps).
🛡️ Mechanical Safety and Guarding
The mechanical hazards in resistance welding equipment include crushing (between moving electrodes), shearing (in seam welder drive mechanisms), and ejection (of molten metal). The standard requires:
- Two-hand control devices for manual welding stations, preventing the operator’s hands from being in the weld zone during the welding cycle
- Light curtains or safety scanners for automated welding cells, with safety-rated control systems per ISO 13849-1 (PL d or higher)
- Anti-tie-down monitoring for two-hand controls to ensure both switches are released between cycles
- Chip and splash guards to contain weld spatter and electrode debris
✅ Practical Recommendation
When designing a resistance welding work cell, pay particular attention to the electrode maintenance procedure. Operators must regularly dress (re-contour) the welding electrode tips, which requires reaching into the weld zone. The safety system must include a “setup mode” that allows electrode access at reduced speed and force (< 150 N limit per ISO 13854) while maintaining operator safety.
When designing a resistance welding work cell, pay particular attention to the electrode maintenance procedure. Operators must regularly dress (re-contour) the welding electrode tips, which requires reaching into the weld zone. The safety system must include a “setup mode” that allows electrode access at reduced speed and force (< 150 N limit per ISO 13854) while maintaining operator safety.
🔧 Installation and Environmental Considerations
The standard also addresses installation requirements that directly affect the performance and safety of resistance welding equipment:
- Cooling water systems: Resistance welding transformers and electrodes require substantial cooling. The standard requires flow monitoring, temperature sensors, and automatic shutdown on cooling failure. Minimum flow rates must be specified by the manufacturer.
- Compressed air supply: Pneumatic electrode actuation systems require filtered, regulated air. Loss of air pressure must trigger a safe stop, and the electrodes must retract to a safe position.
- EMC considerations: Resistance welding generates significant electromagnetic interference due to the high-current pulses. The standard references IEC 61000-6-4 (emission) and IEC 61000-6-2 (immunity) for industrial environments. Note that conducted emissions on the mains supply may require passive harmonic filters or active power factor correction.
📊 Risk Assessment and Documentation
IEC 62135-1:2015 requires the manufacturer to perform and document a risk assessment following the iterative process of ISO 12100. The risk assessment must cover all lifecycle phases: transport, installation, commissioning, operation, maintenance, decommissioning. The residual risks must be documented in the instruction manual, and safeguards must be verified for effectiveness.
❓ Frequently Asked Questions
Q1: Does IEC 62135-1 apply to welding guns used in robotic applications?
Yes, but with additional considerations. The welding gun itself must comply with IEC 62135-1, while the robotic system integration follows ISO 10218-1 and ISO 10218-2 (robot safety). The interface between the robot controller and the welding control must be safety-rated, particularly for the “weld gun open/close” command and the “welding current on” interlock.
Q4: What is the difference between a Type A and Type B RCD for welding equipment?
A Type A RCD detects sinusoidal AC residual currents and pulsating DC residual currents. A Type B RCD additionally detects high-frequency AC residual currents and smooth DC residual currents — which are commonly generated by inverter-type resistance welding power supplies. For welding equipment with inverter technology operating above 50 Hz, Type B RCDs are strongly recommended.
Q3: How often must safety-critical components in a resistance welding machine be verified?
The standard requires periodic verification intervals to be specified by the manufacturer based on the risk assessment. Typical intervals are: daily (electrode condition, coolant flow, air pressure), monthly (safety relay/PLC logic verification, light curtain alignment), and annually (full functional safety test including stop time measurement, protective earth continuity, and insulation resistance testing).
Q4: Are there specific requirements for electromagnetic field (EMF) exposure?
IEC 62135-1 does not specify EMF limits, but the manufacturer must assess EMF exposure per the EU EMF Directive (2013/35/EU) or applicable national regulations. The extremely high welding currents generate strong magnetic fields near the secondary loop. Mitigation strategies include minimizing the loop area of the secondary circuit, using coaxial secondary cables, and implementing magnetic shielding around the weld zone.
