Grounding Resistance Range

Common Standard Values for Grounding Resistance

• Working grounding (functional grounding): Resistance ≤ 4 Ω
• Protective grounding:
  
  
  • ≤ 4 Ω (grounded neutral system)
  • ≤ 10 Ω (ungrounded neutral system)
    
    
• Repeated grounding: Resistance ≤ 10 Ω
• Lightning protection grounding: Resistance ≤ 10 Ω
• Static electricity grounding: Resistance ≤ 100 Ω
• Combined grounding (lightning + protection, etc.): Resistance ≤ 10 Ω
• Transformers below 100 kVA: Resistance ≤ 10 Ω
• Special locations and equipment grounding: Resistance ≤ 2 Ω
  
  

The smaller the grounding resistance, the better.

The larger the insulation resistance, the better.