Resettable fuses aim for telecomms protection

HVR250 series PPTC fuses are optimised to provide overvoltage and overcurrent protection for telecomms and networking equipment.

Wickmann's range of Polyfuse fully resettable fuses has been widened with the introduction of the HVR250 series.

Positive polymeric temperature coefficient (PPTC) devices, the fuses are optimised to provide overvoltage and overcurrent protection for telecomms and networking equipment which has to comply with the International Telecommunications Union's K20, K21, K45 and Telecordia GR-974 requirements.

The HVR250 through-hole fuses can be supplied in uncoated and coated versions with hold currents from 80 to 180mA.

Rated operating voltage is 60V and maximum interrupt voltage 250V to comply with the AC power cross tests.

Lead-free fuses are available initially for 80 and 180mA hold currents.

Overvoltages, 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 can overload the protection components and overheat the tip and ring lines on the equipment's input, resulting in damaged components and failed equipment.

The HVR250 fuses protect devices from induced currents and automatically reset on correction of the fault, leading to greatly reduced maintenance costs.

The Wickmann Polyfuse resettable range comprises radial-leaded, axial-leaded straps, surface-mount and disc-type fuses, all manufactured from PPTC material that consists of conductive carbon black particles.

Under normal operating conditions, strings of carbon particles conduct current while exhibiting a very low internal resistance.

When the fuse's trip or fault current is exceeded, the particle strings break up and disburse randomly followed by a rise in internal resistance of several orders of magnitude.

This rapid increase in resistance limits current flow to nearly zero, effectively protecting the downstream circuitry.

When the fault subsides or the power is removed, the Polyfuse cools and resets, returning to its pretripped state.

All Wickmann Polyfuse components comply fully with the relevant international standards.

Back to top