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United States
Tel: 901.252.8000
Fax: 901.252.1354
Technical Services
Tel: 888.862.3289
OS Series Back-Up Current-Limiting Fuses
Power & High Voltage —
& Hi-Tech
Fuse Products
The Trans-Guard
OS Shorty is a back-up type current-limiting fuse designed for application within
distribution transformers. Its ability to significantly reduce fault energy and its very high interrupting
capability (50,000 amperes symmetrical) provide state-of-the-art protection against today’s ever-
increasing available fault currents.
OS Shorty fuses are compact in size and allows for easier installation in smaller distribution transformers.
As a back-up type current-limiting fuse (refer to ANSI C37.40 for fuse definitions), the Trans-Guard
Shorty must always be applied in series with a properly sized low-current protective device. This device is
typically an under-oil expulsion fuse (i.e. Bay-O-Net fault or load sensing link, terminal board weak link,
etc.). The expulsion fuse and the current-limiting fuse are each selected to provide fault protection over a
certain range of currents. The expulsion fuse is chosen to clear the low-magnitude currents such as those
caused by faults that occur external to the transformer, high-impedance faults within the transformer, and
in the case of load sensing links, transformer overloads. Such currents are generally below the minimum
interrupting current rating of the current-limiting fuse. The back-up type current-limiting fuse is selected
so as to clear all other currents.
In addition to interrupting the fault currents resulting from low-impedance faults within the transformer,
the back-up current-limiting fuse serves the very important function of limiting the amount of energy
that is let through to the source of the fault to a value below the withstand capability of the transformer
tank. By doing this, the current-limiting fuse minimizes the likelihood of disruptive equipment failures
(i.e. transformer tank ruptures, accessories being damaged or broken loose from their mountings, etc.).
No other protective device is available to similarly reduce the risk of disruptive transformer failures.
Highest current ratings available in a single fuse body
minimizes the costs and physical space associated with
paralleling two fuses to achieve the desired current rating
Smaller physical size allows for easier installation
Rigorous testing to meet ANSI/IEEE standards
Durable design features machined brass end caps,
filament-wound high-temperature epoxy tubular bodies,
sand filler and a hermetic sealing system
High fault current interrupting capability — 50,000
amperes symmetrical for most ratings
Broad range of fuse ratings—30 amps–400 amps
Elevated rated maximum voltage — 10kV,17.2kV, 25.5kV
and 38kV for many designs
OS Shorty Fuse