Lightning Surge Overvoltage Protection for Low-Voltage Equipment Placed Outdoors in TT System

When a TT system is used for earthing a low-voltage distribution line, the conductive enclosure of the equipment is grounded separately from the system ground for the power line. In such a case, lightning protection depends on the installation of surge protective devices (SPD) on the equipment side. However, in newer systems, a protective earth (PE) line is wired from the power substation for stable operation and connected to the PE line in the outdoor equipment. In this case, the SPD of the distribution board can suppress the overvoltage on the equipment side. In this article, the overvoltage generated between the power and grounded PE lines of the equipment using a vinyl-insulated vinyl-sheathed flat-type cable for a low-voltage distribution line was examined using transient circuit analysis. Then, we demonstrated countermeasures to achieve electric shock and lightning overvoltage protection.