PZH III V 3+1 is a three-phase surge arrester type 3 according to EN 61643-11 suitable for use in TNS, TNC and TT systems. These are parallel devices intended for protection of electronic appliances against impulse surge. All varistors in PZH III V 3+1device are fitted with thermal fuses to prevent short and also permanent overloading. PZH III V 3+1 units are to be connected as near to the protected electronic appliance as possible. The right function of PZH III V 3+1/275/5, PZH III V 3+1/480/5 and PZH III V 3+1/600/5 devices is indicated by three green LED diodes. The function failure of PZH III V 3+1/275/5 S, and PZH III V 3+1/480/5 S devices is indicated by target disconnection of mechanical thermal fuses which react to varistors overheating above c. 120°C. If one of the three thermal fuses reacts, the non-potential contact FAILURE disconnects at the same time (in case of S version only).