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Resettable Fuse Protects Telecom, Network Equipment

The Polyfuse HVR250is a polymer-based positive temperature coefficient (PPTC) device, designed to protect telecommunications and networking equipment against lightning strikes and power crosses.


The HVR250 resettable fuses are optimized to provide overcurrent for xDSL and ISDN modems, splitters, and MDF equipment that must comply with ITU K.20, K.21, K.45 and Telcordia GR-974 requirements. K.20 addresses central office switching equipment including line cards, modems, splitters and multiplexers, whereas K.21 specifies requirements for customer premises equipment including modems, fax machines, caller ID boxes, voice over IP appliances and PBX equipment.

K.45 covers the requirements and procedures for equipment installed between a central office and customer premises. Telcordia GR-974 outlines the requirements for main distribution frame (MDF) modules and network interface devices (NID).

Overvoltages, which are typically caused by lightning surges or AC power faults, are usually limited by using gas tube surge arresters or varistors. However, this can produce high fault currents that may overload the protective circuitry and overheat the tip and ring lines on the equipment’s input, resulting in damaged components and failed equipment. HVR250 fuses protect the equipment from induced current conditions and automatically resets after correction of the fault, reducing the equipment service costs..

The HVR250 is available in coated and uncoated versions with hold currents from 80 to 180mA. The HVR250 is designed to withstand a maximum of 250VAC interrupting voltage.

Wickmann


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