Earthing - IET

Key: T = Terre (earth), N = neutral, C = combined, S = separate

TN-S

• Neutral connected to earth at supply only
• Max Ze 0.8Ω

TN-C-S

• Protective Multiple Earthing (PME)
• Supply neutral connected to earth at source and at intervals along the run
• Max Ze 0.35Ω

TT

• Installation has own earth electrode local to the install
• Distributor doesn’t provide an earth

TN-C

• Uncommon
• Requires exemption from Electrical Safety, Quality & Continuity Regulations

IT

• Uncommon
• Not permitted for Low Voltage public supply
  • Source is not directly earthed