Earthing Systems

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TN-S, TN-C-S (PME) and TT systems.

TN-S

Separate neutral and earth back to the source, usually via cable sheath. Typical max Ze 0.8 Ω.

TN-C-S (PME)

Combined PEN conductor in the supply; separated at the origin. Typical max Ze 0.35 Ω. Restrictions apply for EV charging and outdoor equipment (722.411.4).

TT

Installation earth electrode. RCD needed for fault protection; RA × IΔn ≤ 50 V. Electrode resistance above 200 Ω may be unstable.

Key regulations

312.2411.4411.5542