TN-S vs TN-C-S vs TT vs IT — Earthing System Comparison Poster

Understanding earthing systems is fundamental to electrical design, yet many engineers struggle to visualise the differences between TN-S, TN-C-S, TT, and IT configurations. This A4 portrait poster presents each of the four earthing systems as a clear single-line diagram showing the source transformer, distribution network, and installation earthing arrangement. Colour-coded conductors (brown for line, blue for neutral, green-yellow for earth, and dashed for PEN) make it easy to trace the fault current return path for each system. Below each diagram, a characteristics panel lists the key properties: earth fault loop impedance behaviour, touch voltage risk, RCD requirements, and the specific IEC 60364-1 clause that defines the system. A comparison table at the bottom summarises mandatory protection devices for each system — TN-S and TN-C-S rely on overcurrent protection with RCDs recommended, TT systems require RCD protection as the primary earth fault device, and IT systems need insulation monitoring devices (IMDs) with alarm-on-first-fault capability. The poster also covers where each system is typically used: TN-S in new UK and Australian installations, TN-C-S (PME) for UK supply networks, TT in rural areas and developing countries, and IT in hospitals, mines, and process plants where continuity of supply is critical. Essential for electrical engineering students, apprentices learning system design, and experienced engineers who need a quick visual reference when specifying protection schemes.