Talk in detail about the main differences between the safety standards UL 62368 and UL 60950

With the deep integration of AV/ITE/ICT technologies, the 'prescriptive' framework of UL 60950-1 has become inadequate for cross-domain products. UL 62368-1, with its core philosophy of 'hazard-based and performance-based' safety, achieves a leap from 'rule compliance' to 'risk management,' establishing a unified AV/ICT safety system. This article focuses on the core differences and key implementation points between the two standards, providing a concise guide for product upgrades.

The Essential Shift in Core Philosophy and Scope of Application

1.1 Divergence in Safety Philosophy

UL 60950-1: Prescriptive compliance, establishing 'one-to-one' mandatory requirements (such as reinforced insulation, V-0 flame retardancy) based on known risks. Engineers only need to follow the rules, applicable to traditional ITE equipment.

UL 62368-1: Risk-driven paradigm, classifying hazards into three levels of energy sources (ES1/ES2/ES3). It requires achieving safety objectives through 'hazard identification - classification assessment - precise protection,' allowing for technological innovation and elevating engineers to 'safety designers.'

1.2 Expansion of Applicable Scope

Upgrades in Key Technical Requirements and Engineering Impact

2.1 Insulation and Spacing

UL 60950-1: Three-dimensional table lookup based on voltage + pollution degree + material group, with simple logic.

UL 62368-1: Four-dimensional assessment based on working voltage + withstand voltage + frequency + environment. Clearances need to consider transients (e.g., clearance for mains-powered equipment may increase from 2.5mm to 4.0mm). High-frequency circuits require tracking-resistant materials. PCB and transformer designs need to be revisited.

• Clearance: Requires calculating both the 'minimum spacing corresponding to normal working voltage' and the 'withstand spacing corresponding to transient overvoltages (e.g., lightning surge, grid fluctuations),' taking the larger value. For example, a mains-powered adapter may need to consider ±2kV differential mode surge, potentially increasing clearance from 2.5mm to 4.0mm.
  
• Creepage Distance: Introduces frequency correction factors. For high-frequency circuits >30kHz common in switch-mode power supplies, due to increased risks of corona discharge and electrochemical corrosion, stricter CTI (Comparative Tracking Index) grading per GB/T 4207 is required, or materials with CTI≥600 should be selected.
  
• Engineering Impact: PCB layout needs to be re-planned for isolation zones (especially between primary-secondary and high-low voltage sections), potentially increasing board size. High-frequency transformers need specific certifications like VDE 0884-11 to verify insulation system's temperature and voltage withstand capabilities.
  

2.2 Fire Safety

UL 60950-1: Component-level flame retardancy requirements (e.g., VW-1 cables).

UL 62368-1: System-level control, linking enclosures to PS1/PS2/PS3 power source classifications. PS2/PS3 equipment require 5VA-rated enclosures. Cables must pass stringent IEC 60332 flame tests, potentially involving material and mold changes.

• Power Source Classification Logic: PS1 (Low power source, ≤15VA), PS2 (Moderate power source, 15VA~1kVA), PS3 (High power source, >1kVA). Higher power necessitates stricter fire safety requirements.
  
• Enclosure Materials: Enclosures associated with PS2/PS3 circuits must meet UL 94 5VA rating (compared to V-0, adds impact resistance test with a 500g weight), replacing common HB ratings (Horizontal Burning) from 60950-1.
  
• Internal Wiring: Wiring connecting to PS2/PS3 circuits must pass IEC 60332-1-2 (single vertical flame test) or IEC 60332-3-24 (bunched cable flame test), requiring cables not to drip and flame spread rate ≤250mm/min.
  
• Engineering Impact: Companies may need to change enclosure plastic materials (e.g., from ABS to flame-retardant modified PC+ABS), potentially requiring mold modifications and cost increases. Internal wiring needs reselection, preferring LSZH (Low Smoke Zero Halogen) flame-retardant cables.
  

2.3 Temperature Control

UL 60950-1: Relative temperature rise limits, focusing on component protection.

UL 62368-1: Absolute touch temperature limits (metal gripping surfaces ≤55°C), focusing on user safety, requiring optimized heat dissipation or added thermal insulation design.

2.4 Coverage of Emerging Technologies

UL 62368-1 addresses specific requirements for new-generation electronic devices not systematically covered by UL 60950-1. These include lithium battery safety (BMS quadruple protection), acoustic energy (≤100dB(A)), optical radiation (IEC 62471), wireless charging (magnetic field limits + FOD detection), and other specific requirements, filling gaps for cross-domain products.

Upgrade Strategy and Conclusion

Product upgrade is recommended in three steps: 1. Gap analysis, benchmarking against core differences; 2. Risk assessment, identifying energy sources and protection gaps; 3. Design optimization, prioritizing clearance, fire safety, and temperature issues.

The transition from UL 60950-1 to UL 62368-1 represents an upgrade in safety engineering thinking. Despite technical and cost challenges, this shift aligns with industry convergence trends, lays a safety foundation for future product innovation, and is an important marker of industry professionalization.