Fuse & Protection Home Information Enquiry

PROTECTION CLASS

Utilisation Classes
gL/gG Full Range breaking capability, General Application
gM Full Range breaking capability, Motor Application
aM Partial Range breaking capability, Motor Application
Cable Protection
By using 'gG' fuse link of current rating equal to, or less than, the cable rating, both overload and short circuit protection is easily achieved.
Motor Circuit Protection
Fuse Links are selected to withstand motor starting surges, typically 7x full load current (FLC) for the run up period in the case of a direct on line (DOL) start motor, and provide back up protection, including Type 2 Co-ordination with the motor starter and its associated cables.
Extended range 'gM' fuse links allow economies to be made in the sizes of associated equipment.
Transformer Protection
Fuse links are selected to with stand the transformer magnetising inrush current surge, generally assumed to be around 10-12 x full load current (FLC) for 0.1 seconds, in addition to any permissible overloads.
Capacitor Protection
Power factor correction capacitors need to have fuse links capable of withstanding the transient currents associated with switching as well as the capacitor tolerance and generated harmonics. Selection of a fuse link of 1.5-2X capacitor full load current (FLC) will usually be suitable.
Semiconductor Protection
Fuse links with high speed characteristics are selected to provide low energy and let through current and can be closely co-ordinated with the energy (I2t) and peak surge ratings of power electronics devices such as diodes and thyristors.
Household Protection
Fuse links are selected and applied to provide both short circuit and cable overload protection from the incoming house service cut out, through the consumer unit which may contain fuse links or MCB's, right down to final circuit protection via the plug fuse link.
Fluorescent Lighting
Fuse links protecting fluorescent lighting loads must be able to withstand the high inrush surges associated with the starter circuit which may be as high as 50 or 100X load current for times less than 0.5ms. Selection of a fuse link of 2X load current will normally be adequate.

GENERAL APPLICATION NOTES

Voltage Rating
Fuse links are voltage sensitive devices and it is important to note that satisfactory operation of a fuse link under fault conditions is dependent upon the applied voltage. They must not therefore, be applied in cicuits above their voltag capability. They can however, satisfactorily in cicuits at lower voltages.
Current Rating
The Fuse link continuous current rating should not be less than the full load current of the circuit, although temporary overloads such as motor starting surges can exceed this value in accordance with the time current characteristic.
Breaking Capacity
Fuse link are generally assigned standerdised breaking capacityies, normally in excess of any fault current likely to be encountered in service.
Ambient Temperature
Fuse links are thermal devices and as such may require some derating when used at elevated ambient temperatures. Certain fuse links, notably those for the protection of semiconductor devices, may be uprated when subjected to forced air cooling.
Discrimination
It is very common to find HRC fuse links, particularly low voltage types, in series with one another in electrical installations, and discrimination is the ablility of such fuse links to operate selectively to disconnect only the faulty part of the installation.
Descrimination can be checked by ensuring that the time current characteristics, including their tolerances, do not overlap at any point and that the total let through energy (I2t) of the minor fuse link does not exceed the pre-arcing (I2t) of the major fuse link at the applied system voltage.

BUSSMANN - CIRCUIT PROTECTION SOLUTIONS

Bussmann is a leading manufacturer of cicuit protection solutions, producing and marketing over 20000 products for use within many applications. Electrical Distribution, Electronics, Telecommunications, Automotive, and Power Semiconductor.
Bussmann offer a broad range of Fuse Links, Fuse HOlders, Fuse Blocks and Fuse Switch Disconnectors designed and manufactured to DIN BS and UL Standards.
UL TERMS FOR FUSES INFORMATION
Ampere
The measurement of intensity of rate of flow of electrons in an electric circuit. An ampree is the amount of current that will flow through a resistance of one ohm under 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.
Arcing Time
The amount of time from the instant the fuse link has melted until the overcurrent is interrupted or cleared.
Breaking Capacity
(See Interrupting Rating)
Cartridge Fuse
A fuse consisting of a current responsive element inside a fuse tube with terminals on both ends.
Class CC Fuses
600V, 200000 ampere interrupting rating, branch circuit fuses with overall dimensions of 13/32" x 1 1/2". Their design incorportates a rejection feature that allows them to be inserted into rejection fuse holders and fuse block that reject all lower voltage, lower interrupting rating 13/32" x 1 1/2" fuses. They are available from 0.01amps to 30amps.
Glass G Fuses
480V, 100000 ampere interrupting rating branch circuit fuses that are size rejecting to eliminate over-fusing. The fuse diameter is 13/32" while the length varies from 15/16" to 2 1/4". these are available in ratings from 1 amps to 60amps.
Class H Fuses
250V and 600V, 10000 ampere interrupting rating branch circuit fuses that may be renewable or non-renewable. These are available in ampere rating of 1 amp to 600amps.
Class J Fuses
These fuses are rated to interrupt a minimum 200000 amperes AC. They are labelled ass "Current Limiting", are rated for 600Volts AC and are not interchangeable with other Class K Fuses. These are fuses listed as K-1, K-5 or K-9 fuses. Each subclass has designed I2t and Ip maximums. These are dimensionally the same as Class H fuses and they can have interrupting ratings of 50000, 100000 or 200000 amps. These are current limiting. However, they are not marked 'current limiting' on their label since they do not have a rejection feature.
Class K Fuses
These are fuses listed as K-1, K-5 or K-9 fuses. Each subclass has designated I2t and Ip maximums.. These are dimensionally the same as Class H fuses and they can have interrupting ratings of 50000, 100000 or 200000 amps. These fuses are current limiting. However, they are not marked 'current limiting on their label since they do not have a rejection feature.
Class L Fuses
These fuses are rated for 601 to 6000 amperes and are rated to interrupt a minimum of 200000 amperes AC. They are labelled 'current limiting' and are rated for 600volts AC. They are intended to be bolted into their mountings and are not normally used in clips. Some Class L fuses have sdesigned-in time delay features for all purpose use.
Class R Fuses
These are high performance fuses rated 1/10 to 600 amps in 250 volt and 600volt ratings. All are marked 'current limiting' on their label and all have a minimum of 200000 amp interrupting rating. They have identical outline dimensions with the Class H fuses but have a rejection feature which prevents the user from mounting a fuse of lesser capabilities (lower interrupting capacity) when used with special Class R Clips. Class R fuses will fit into either rejection or non rejection clips.
Class T Fuses
An industry class of fuses in 300 volt and 600 volt ratings from 1amp to 1200amps. They are physically very small and can be applied where space is at a premium. They are fact acting and time-lag fuses, with an interrupting rating of 200000 amps RMS.
Class of Fuses
The industry has developed basic physical specifications and electrical performance requirements for fuses withvoltage ratings of 600 volts or less. These are known as standards. If a type of fuse meets the requirements of a standard, it can fall into that classes are K, RK1, RK5, G, L, H, T, CC and J.
Current Limitation
A fuse operation relating to short circuits only. When a fuse operated in its current limiting rang, it will limit the instantaneous peak cycle. Also, it will limit the instantaneous peak let-through current to a value sustantially less than that obtainable in the same circuit if that fuse were replaced with solid conductor of equal impedance.
Fast Acting Fuses
A fuse which opens on overload and short circuits very quickly. This type of fuse is not designed to withstand temporary overload currents associated with some electrical loads.
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 ogten used to protect solid state devices.
Interrupting Rating (Breaking Capacity)
The rating which defines a fuse's 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 overcurrent protective device is intended to interrupt under standeard test conditions."
Time Delay Fuse
A fuse with a built in time delay that allows temporary and harmless inrush currents to pass without opening, but is so designed to open on sustained overloads and short circuits.