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

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.

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.