Analysis of touch voltage and electric shock risk before and after installation of equipotential bonding in the sewage treatment plants

The purpose of this study is to derive the risk of electric shock based on the KEC (Korea Electro-technical Code), which was fully implemented in Korea in 2022, and IEC-60479. Therefore, a sewage treatment facility, where the risk of electric shock due to leakage current is high due to the possibility of damage to the insulation parts of electrical equipment caused by high humidity and the presence of corrosive gases, was selected. The risk of electric shock was analyzed in the event of leakage current occurring in the electrical equipment at the selected facility. To achieve the objectives of this study, the grounding resistance of the facility was measured to observe the trends in the management state of the grounding resistance. The resistance values of protective conductors and grounding conductors connected to exposed conductive parts and extraneous conductive parts were also measured. Additionally, based on the KEC, the grounding system was analyzed, and the touch voltage occurring during electrical leakage was calculated. Based on this, the risk of electric shock was analyzed according to the current flow using IEC-60479. As a result of measuring the resistance values of protective conductors, it was found that some protective conductors exceeded 1[Ω]. In all facilities, the risk of electric shock in the AC-4.2 range (with a 50% or higher probability of ventricular fibrillation) was observed when electrical leakage occurred. Additionally, when assuming the implementation of equipotential bonding, the analysis of electric shock risk revealed AC-3 range (potentially reversible effects on the heart) in two locations, and AC-2 range (no generally perceived physiological effects) in all other sections. These findings emphasize the urgent need for on-site implementation of equipotential bonding in compliance with the KEC. Furthermore, resistance measurement and management of the protective conductors are necessary.