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From lightning concepts to low-voltage power-line SPD products—a structured guide for engineers, panel builders, and local partners.

3. Low-Voltage Power System Basics · Page 2 of 6

TN, TT and IT Earthing Systems

System earthing changes SPD selection and N-PE behavior.

TN systems

In TN-S / TN-C-S, PE is solidly referenced. SPD connections to PE are straightforward, but you must still respect backup fuse / breaker coordination.

TT systems

TT systems rely on earth electrodes with higher impedance. Follow manufacturer guidance for SPD topology and residual current device interactions.

IT systems

IT systems may leave one point isolated or impedance-earthed. SPD selection needs special attention to avoid nuisance issues during first faults.

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