FUSE Selection GUIDE
Fuse Application
The following list is provided to assist you in narrowing down the possibilities of your fuse search. It is by no means comprehensive.
| Feeder Circuit Sectionalizing | CLE, HLE, HCL, RBA |
| Fused Switch/Switchgear | CLE, HLE, RBA |
| Power Transformer | CLE, HLE, RBA, DBA |
| Substaion Service Transformer | RBA |
| Underground Distribution Transformer | CX, CLT |
| Pole Mounted Transformer | DBU |
| Pad Mounted Distribution Transformer | DBU |
| Motor Starter | CLS, HLE |
| Potential Transformer | CLPT |
| Capacitor Bank | CX, HLE, CLE |
| Mine Rectifiers | CX |
Current Limiting Fuses
CLE & HLE -E Rated |
CLS - R Rated |
| Ratings: 2-15kV, 10E-1350E | Ratings: 2-8 kV, 2R-44R |
| Applications: SW-Gear, Sectionalizing | Applications: Motor Starter |
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| CLE = Westinghouse Form Factor | CLE = Westinghouse Form Factor |
| HLE = GE Form Factor | HLE = GE Form Factor |
| UL Listing on 5/15 kV | UL Listing on 5/15kV |
| Offered in Bolt-In or Clip Design | Offered in Bolt-In or Clip Design |
CLPT |
CX - C Rated |
| Ratings: 2-38kV, 0.25E-10E | Ratings: 2-15kV, 3.5-300C |
| Applications: Potential/Control TX's | Applications: Dist TX's |
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| Indicator Optional |
Expulsion Fuses
RBA/RDB Refillable |
DBU Replaceable |
DBA Refill |
| Ratings: 8.3-38kV, 0.5-7.20E | Ratings: 17-38kV, 3-200A | Ratings: 8-169kV, 0.5-200E |
| Applications:SW-Gear, Sectionalizing | Applications:Pad-Mount, Pole-Top | Applications: Power, Distribution |
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| Offer Disconnect or Non-Disconnect | Sealed Design: In or Outdoor | For Westinghouse Equipment |
| Indoor or Outdoor Versions | Elect/Mech Eqiv. to Competition | Refill Units Only |
| Fuse Cartridge is Replaceable | Outdoor Application | |
Fuse Terms
Our take on definitions for basic fuse terminology. Go to Fuse Applications to determine specific fuse usage.
Ampere
The measurement of intensity of rate of flow of electrons in an electric circuit. An ampere is the amount of current that will flow through a resistance of one ohm under a pressure of one volt.Ampere Rating
The current carrying capacity of a fuse. When a fuse is subjected to a current above its ampere rating, it will open the circuit after a predetermined period of time.Ampere Squared Seconds (I²t)
The measurement of heat energy developed within a circuit during the fuses clearing. It can be expressed as melting - I²t, arcing - I²t, or the sum of them as clearing - I²t. "I" stands for effective let-through current (RMS), which is squared, and "t" stands for time of opening, in seconds.Arching Time
The amount of time from the instant the fuse link has melted until the over current is interrupted, or cleared.Braking Capacity
The rating which defines the fuses ability to safely interrupt and clear short circuits. This rating is much greater than the ampere rating of a fuse.The NEC defines interrupting rating as "The highest current at rated voltage that an over current protective device is intended to interrupt under standard test conditions."
Clearing Time
The total time during the beginning of the over current and the final opening of the circuit at rated voltage by an over current protective device. Clearing time is the total of the melting time and the arcing time.Current Limitation
A fuse operation relating to short circuits only. When a fuse operates in its current limiting range, it will clear a short circuit in less than 1/2 cycle. Also, it will limit the instantaneous peak let-thru current to a value substantially less than that obtainable in the same circuit if that fuse were replaced with a solid conductor of equal impedance.Disconnect Mounting
The disconnect mounting allows the fuse unit to be removed (off load) using an insulated hook stick. The hook-stick grabs a pull ring and disconnects the fuse unit, which may then be lifted out of its mounting.End Fittings
End fittings are metal parts that attach to each end of a fuse unit’s ferrules (end caps). As previously mentioned, they are used solely with disconnect fuse applications or when converting a non-disconnect to a disconnect fuse configuration. When end fittings are ordered, a fitting for each end of the fuse is included. Keep in mind that end fittings can become damaged in use and, therefore, are sold separately from the live parts when necessary. It is not necessary to purchase an entire set of live parts when only the end fittings are required.High Speed Fuses
Fuses with no intentional time-delay in the overload range and designed to open as quickly as possible in the short circuit range. These fuses are often used to protect solid state devices.Live Parts
Live parts were discussed as part of the “Mounting” definition. Everything above the insulators on the mounting excluding the fuse unit, fuse holder, and the fuse end fittings (if required) are considered the live parts. Fuse end fittings are discussed next and are not required with non-disconnect live parts, but are required and included with disconnect live parts. Live parts may be sold separately as replacement parts or for new OEM applications.Melting Time
The amount of time required to melt the fuse. Link during a specified over current.Mounting
A mounting provides all the necessary parts to safely mount a fuse in its intended piece of equipment. The base is the metal support to which all other pieces attach. Insulators attach to the base and insulate the live fuse unit from the base and everything beyond the base. Live parts are the parts of the mounting that are energized once electricity is flowing. The live parts provide the means to hold the fuse unit in place, electrical contact, and a place to make line and load connections.Non-Disconnect Mounting
A non-disconnect mounting does not provide a means for removing the fuse unit until the circuit is dead and the fuse unit can be removed manually. The fuse unit is held in place by friction through the use of fuse clips or by a cross bar.OHM
The unit of measure for electric resistance. An ohm is the amount of resistance that will allow one ampere to flow under a pressure of one volt.OHM`s LAW
The relationship between voltage, current, and resistance, expressed by the equation E=IR, where E is the voltage in volts, I is the current in amperes, and R is the resistance in ohms.Over Current
A condition which exists on an electrical circuit when the normal load current is exceeded. Over currents take on two separate characteristics--overloads and short circuits.Overload
Can be classified as an over current which exceeds the normal full load current of a circuit. The current does not leave the normal current carrying path of the circuit--that is, it flows from the source, through the conductors,through the load, back through the conductors, to the source again.
Peak Let-Thru Current, IP
The instantaneous value of peak current let-thru by a current limiting fuse, when it operates in its current limiting range.Power vs. Distribution
The differentiation is intended to indicate the test conditions and where fuses are normally applied on an electrical system, based on specific requirements for generating sources, substations and distribution lines. Each class has its own unique set of voltage, current and construction requirements (see ANSI C37.42, .44, .46 and .47).Replaceable Fuse Unit:
A replaceable fuse unit is a phrase used to describe a fuse that does not have a separate holder and refill assembly. In a replaceable fuse unit, the fuse is its own holder and is completely replaced after interruption.Resistive Load
An electrical which is characteristic of not having any significant inrush current. When a resistive load is energized, the current rises instantly to its steady state value, without first rising to a higher value.R.M.S. Current
The R.M.S. (root-mean-square) value of any periodic current is equal to the value of the direct current which, flowing through a resistance, produces the same heating effect in the resistance as the periodic current does.Short Circuit
An over current which exceeds the normal full load current of a circuit by a factor many times (tens, hundreds or thousands greater). The over current also leaves the normal current carrying path of the circuit--it takes a "shortcut" around the load and back to the source.Voltage Rating
The maximum open circuit voltage in which a fuse can be used, yet safely interrupt an overcurrent. Exceeding the voltage rating of a fuse impairs its ability to clear an overload or short circuit safely.
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 above 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.
A Current Limiting Power Fuses will always be E-rated, but a Current Limiting Distribution Fuse can either be C-rated or R-rated.
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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Fuse Class - Expulsion
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Fuse Class - Current Limiting
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| 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. | 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. | |
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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.
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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.
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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. |
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.
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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.
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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. | |
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Expulsion Fuses |
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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.