By Littelfuse Inc 107
The Littelfuse TMOV 25S and TMOV34S varistor series are specifically designed for applications that must meet the requirements of the limited current, abnormal overvoltage test in the UL1449 (3rd edition) surge protection device (SPD) standard. The TMOV 25S and TMOV 34S series meet the surge suppressor component recognition requirements of UL1449 for both cord-connected and permanently connected SPD end products in a single integrated package. A patented, thermally-responsive element within the body of the varistor will open the device in case of overheating, due to abnormal overvoltages.
The varistors offer high surge current ratings up to 20 kA for TMOV 25S and 40 kA for TMOV 34S. The thermally protected varistors consist of a 25 or 34 mm²-format varistor element (MOV) with an integral thermally activated element. This element is designed to open in the event of overheating due to abnormal overvoltage, limited current conditions. A number of devices include a "monitor" lead that may be connected to signaling circuitry to indicate if the MOV has been disconnected from the circuit. TMOV 34S series and TMOV 25S varistor series devices offer quick thermal response, due to the close proximity of the integrated thermal element to the MOV body. The integrated configuration also offers lower inductance than most discrete solutions, which helps ensure faster clamping response to overvoltage transients.