How should I select the proper fuse amperage when I know the circuit amperage? Always follow NEC guidelines for applying low-voltage fuses. Time-delay fuses should be used for inductive loads and fast-acting fuses used to protect non-inductive loads. What is the difference between interrupting rating and the fuse's ampere rating? The interrupting rating is the maximum amount of energy the device can safely withstand.

The fuse's ampere rating is the amount of current that the fuse will allow through before beginning to operate. Both ratings are determined through testing. The interrupting rating is important because it is a safety rating. If a device with a low interrupting rating is used in circuit that has a higher available fault current the amount of energy that is potentially available if a fault were to occur , the device could potentially fail rupture or explode as it attempts to clear the fault, causing a safety hazard.

Are fuse reducers required for downsizing ampere ratings of Class L fuses? No, fuse reducers are not required or available. The bolt hole patterns of Class L fuses are designed to allow you use smaller ampere ratings.

Yes, fuseholders do require derating. Often times derating for a fuseholder is overlooked by an engineer because it does not specified on the datasheet. Please review the attached document for derating of fuseholders. No - No fuse manufacturer offers Class L fuse blocks. Class L fuses are bolted directly on buss bars or used with bolted-pressure contact switches.

A rejection feature is used to prevent fuses with a lower voltage or interrupting rating such as Class H and Midget fuses from being used in a circuit that needs a higher rating. Class R and CC fuseblocks incorporate a built-in rejection feature while Class J and T blocks reject based on physical size. How can I find out which fuse block or holder I can use with any of your fuse series? The attached file is a cross reference of the appropriate fuseholder or fuse block that can be used with any Littelfuse brand fuse series.

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Can a time delay fuse be used to replace a fast acting fuse? Fast-acting fuses are generally used to protect sensitive components from damage so replacing fast-acting fuses with a time-delay fuse could result in damage to your equipment.

NEC guidelines are also different for applying fast-acting and time delay fuses. Fuse sizing may vary. It is best to thoroughly understand the circuit before making a decision to switch from a fast-acting fuse to one with time delay. The attached datasheet explains the color coding system. Do you have an explanation for your part number nomenclature? Littelfuse Part Number Explanation.

Customers call for a 3AG size solution and we have nothing to offer. For customers requiring a 3AG solution Littelfuse does not offer a fuseholder to fit your needs. Electrically, the series In-Line fuseholder can handle the voltage but they are all rated at 32 Volts because of the risk of shock to the user when the holder is opened.

RK1 fuses can provide better protection because they allow less damaging energy to pass through them while opening blowing. These non-renewable fuses are current-limiting and intended for the protection of components sensitive to short-time overloads, non-inductive loads, and short-circuit protection of motor circuits.

Class CC fuses are available with DC ratings. The interrupting rating is kA rms symmetrical. Class G fuses. These fuses were specifically created for use in lighting and appliance panel boards that are equipped with a special fusible-switch unit.

These are non-renewable cartridge fuses that are for use only in AC circuits where interrupting ratings to kA rms symmetrical are required. These can also be available with DC ratings. The innovative design of this class of fuse was selected so as to prevent the interchangeability with any other fuse class.

Class G fuses are current-limiting and are able to be so labeled per UL , which prescribes the maximum peak let-through and I2t let-through values permitted for this class of fuse. The time delay test feature is optional. Class H fuses. This is a cartridge fuse and is intended for general purpose branch circuit, lighting circuit, and the protection of non-inductive equipment like electric ovens and resistance heaters.

You can select from renewable and non-renewable Class H fuses. The renewable fuses allow the user to replace the internal fusible link after the fuse operates. All Class H units are tested for short-circuit requirements and are available with DC ratings. The short-circuit power factors are relatively high: 0. The actual short-circuit power factors encountered in typical installations are on the order of the above test values, when the available short-circuit current is 10kA rms symmetrical or less.

With respect to the time delay feature of fuses, the renewable types cannot perform the time delay but the non-renewable can. Class H fuses, both non-renewable and renewable, are often misapplied in the electrical industry for a couple reasons. First, their minimal 10kA interrupting rating is easy to exceed in an industrial plant or commercial building.

Second, workers unfamiliar with the differences between devices might be tempted to install more than one link in a renewable fuse. Class J fuses.

These non-renewable fuses are current-limiting and conform to Class J fuses are available with DC ratings. Power fuse safety and test procedures have been established by the U. S, Europe and Asia as performance standards. Power fuses standards of low-voltage volts or less have evolved into distinct classes. Not only when you first specify them, but also when you replace them. To aid in selection, manufacturers produce fuses designated by class.

Many are dual rated and can be used in dc applications. All are current limiting and carry a kA interrupting rating. Some are self-certified up to kA IR. Most RK fuses are time-delay dual element design. Fast acting RK fuses are also available for sensitive or critical component protection applications. Class RK fuses are commonly used in mains, feeder and branch circuits, motors, transformers, solenoids and general purpose circuits.

This means Class RK1 allow less damaging energy to pass through them while opening blowing. Recommended applications for RK1 fuses are the same as RK5 in most cases and as mentioned above, they offer greater current limitation.