Announcing the new “DR” speed SMU-20 fuse units

CHICAGO, June 27, 2005 — S&C Electric Company introduces a new family of high-surge-capacity SMU-20 Fuse Units, filling a market niche not presently served by S&C’s existing fuses. These fuse units were developed in response to customers’ requests for fuses with time-current characteristics similar to “DR” Speed S&C Positrol® Fuse Links used in S&C Type XS Fuse Cutouts, but with the higher peak-load and interrupting capabilities of SMU-20 Fuse Units. They provide the same non-damageability, superior secondary-fault-clearing performance, and tight TCC tolerances for which S&C Power Fuses are renowned.

“DR” Speed SMU-20 Fuse Units are available in ratings of 3DR, 4DR, 5DR, 7DR, 10DR, 15DR, and 20DR amperes, at voltages of 14.4 kV through 34.5 kV. They are intended solely for protection of overhead pole-top transformers in ratings through 100 kVA single-phase at 15 kV, 167 kVA single-phase at 25 kV, and 250 kVA single-phase at 34.5 kV.

The new “DR” Speed SMU-20 Fuse Units feature high adiabatic minimum-melting I2t – approximately the same as that of a 20K fuse link. This means that the probability of “DR” Speed SMU-20 Fuse Units operating due to lightning-induced current surges is low – less than 1% per year – even in high isokeraunic areas. It also means that users can mount the surge arrester directly on the transformer tank, to provide the maximum possible overvoltage protection for the transformer, without concern for nuisance fuse unit operations.

For more information on S&C SMU-20 Fuse Units, visit

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