Fuse
Ordering Guide
Terms to know when
ordering fuses
Four common terms
describe the properties of fuses interrupting method, range of
capabilities, typical areas of application and
current rating. They are as follows:
TYPE ▪ CLASS ▪
APPLICATION ▪ AMP RATING
The illustration to the
left provides an easy to understand diagram of these
properties.
A medium voltage
fuse can either be Current Limiting or Expulsion,
but a
Boric Acid fuse will always be either a K or E-rated.
Power Fuse.
General
Purpose and Backup Fuses will always be Current
Limiting but can be applied in both Distribution and
Power applications.
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Fuse Class - Expulsion
Expulsion Fuse: An expulsion
fuse is a vented fuse in which the expulsion effect of the gases
produced by internal arcing, either alone or aided by other
mechanisms, results in current interruption. An expulsion fuse
is not current limiting and as a result limits the duration of a
fault on the electrical system, not the magnitude.
Boric Acid: A vented expulsion fuse in which the
expulsion effect of gases and water vapor produced by the arc
coming in contact with the fuse's boric acid liner extinguishes
the arc.
Expulsion Power Fuses are divided
into two types “Refillable” and “Replaceable”. Refillable fuses
are constructed so that the inner components can be removed and
reused when the assembly is recharged with a new refill. Since
they reuse the spring and shunt assembly these components can be
constructed with a heavy-duty design which allows the unit to
have a higher Interrupting capability. Since the components are
reused it is easy to change the fuse size by simply changing the
refill. Replaceable fuses have a lower installed cost by
providing a more cost-effective construction. This is generally
at the expense of higher interrupting ratings. Cutler-Hammer
offers both a indoor and an outdoor refillable style fuse.
The indoor refillable fuse is the
“RBA” which stands for Refillable Boric Acid fuse. The outdoor
refillable fuse is “RDB” fuse which stands for Refillable
Dropout boric acid fuse.
Expulsion Fuses
Fuse Class - Current Limiting
Current-Limiting Fuse: A
current limiting fuse is a fuse that, when its current
responsive element is melted by a current within the fuse’s
specified current limiting range, abruptly introduces a high
resistance to reduce current magnitude and duration, resulting
in subsequent current interruption.
Backup, General Purpose and Full
Range. An understanding
of these definitions will help to
ensure proper application of the fuse.
Backup Fuses: A fuse capable of interrupting all currents
from the maximum rated interrupting current down to the rated
minimum interrupting current. Backup fuses are always used in a
series with another interrupting device capable of interrupting
currents below the fuse’s minimum interrupting current.
General Purpose Fuses: A fuse
capable of interrupting all currents from the rated interrupting
current down to the current that causes melting of the fusible
element in no less than one hour. General Purpose fuses are
typically used to protect feeders and components such as
transformers.
Full Range Fuses: A fuse
capable of interrupting all currents from the rated interrupting
current down to the minimum continuous current that causes
melting of the fusible element, with the fuse applied at the
maximum ambient temperature specified by the manufacturer.
Current Limiting Fuses
Fuse
Voltage
Fuses are typically
divided into three voltage classifications:
Cutler-Hammer fuses
correspond with the equipment in which they are
installed.
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A Current Limiting Power Fuses will always be E-rated,
but a Current Limiting Distribution Fuse can either be
C-rated or R-rated.
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The Cutler Hammer Fuse Family
Guide to Ampere Ratings
“E” Designation: Fuses rated 100E or below will melt in
300 seconds at a current value between 2.0 and 2.4 times the E
number. Fuses rated above 100E will melt in 600 seconds at a
current value between 2.2 and 2.64 times the E number. If the
current is higher than 2.4 or 2.64 times the E number, the user
must consult the time-current curves for that particular fuse.
“R” Designation: The fuse will melt in 15 to 35 seconds
when the current equals 100 times the R number. If the current
is higher than 100 times the R number, the user must consult the
time-current curves for that fuse.
“C” Designation: The fuse will melt in 1000 seconds at a
current value, between 1.7 and 2.4 times the C number.
If the current is higher than 2.4 times the C number, the user
must consult the time-current curves for that particular fuse.
“A” Designation: Fuses that do not comply with “E”, “R”,
or “C” designations.
Expulsion fuses can also be E-rated, K-rated and T-rated, and
are also covered in the ANSI standards. The K and T ratings
refer, respectively, to relatively “fast” and “slow” melting
expulsion fuses. Detailed time-current tables would be needed to
adequately define the ratings.
BCLS: Bolt-in version of CLS
fuse.
BHLE: Bolt-in version of HLE fuse.
CLE: Current Limiting E-Rated.
HLE: Current Limiting, E-Rated, Interchangeable with
General Electric and Gould Shawmut.
HLC: Current Limiting, E-Rated, Interchangeable with
Gould Shawmut CL 14.
CX/CXN: Current Limiting Interchangeable with
McGraw-Edison’s. NX Brand Fuses, C-Rated.
CLT: Current Limiting Transformer Fuse.
CLEPT: Current Limiting E-Rated for Potential
Transformers.
CLS: Current Limiting for Motor Starters, R-Rated.
CXF/BCXF/TCXF: Current Limiting Full Range Fuses mainly for the
protection of distribution transformers.
RBA: Refillable Boric Acid Expulsion Fuse (Indoor Use).
RDB: Refillable Dropout Boric Acid Expulsion Fuse
(Outdoor Use).
DBU: Dropout Boric Acid Fuse Interchangeable with S&C’s
SMU-20 Refill.
