Leutron serie EP D ... is a surge protector for equipment, to be installed as close as possible to the equipment. EP D TN 275(/FM) is a two-pole SPD in a single block for a two-pole TN-Power Net Systems. EP D TNC 275(/FM) is a three-pole SPD in a single block for a three-pole TNC-Power Net Systems. EP D TNS 275(/FM) is a four-pole SPD in a single block for a four-pole TNS-Power Net Systems. These devices serve as a category T3 surge protector at the supply end of electrical equipments and systems. The green LEDs shows if the operating voltage is achieved and the protective circuit is in full working condition. They are with a thermal protection NC-contact, which opens if the varistor exceed a certain level of temperature due to overload. These thermal protection is installed in such a way that they only cut off the SPD from the power supply whilst the electrical equipment will not suffer any functioning failure; in that case the green signal LED will go out. Before this happens, the optional remote signal contact will open. The protective circuit is installed in an easy-to-handle compact socket for 35mm DIN rail mounting with screw terminals for wire connection.