Frequently Asked Questions

Education Center

Find the answers to your questions by clicking on one of FAQs below. As always, if you do not find what you are looking for a Littelfuse associate will be happy to assist you. Just click here to access our "Support" section. Once there, you'll be required to select a region so we may route your inquiry to the appropriate associate. Be sure to ask one of our technical support associates to add your question to our FAQ database.

 


Can fuses with an AC voltage rating be used in a DC applications?

Fuses must be rated for the voltage AC or DC in which they will be used. Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating. (Example: LLSRK_ID - 600 VAC, 300VDC) Consult the factory for specific DC voltage ratings.



Does Littelfuse have an Environmental Health and Safety Policy?

Yes, Please see the attached PDF

Littelfuse Environmental, Health and Safety Policy

Environmental Health and SafetyEHSPolicy.pdf


Do you have to derate a fuse to account for the operating temperature?

Yes, This information is in a table on page 4 in the Electronic Designers Guide in the Fuseology section but there is no mention of its existence anywhere outside of this section. A pdf of the page is attached for your convenience.

Temperature Derating For Electronic Fuses

Environmental Health and SafetyELEC_FUSE_TEMP_DERATING.pdf


What is the fuse marking according to IEC standard 127 and how does this translates to Littelfuse's 5x20mm fuse offerings?

Please see the attached file.

5x20mm IEC Fuse Marking

Environmental Health and SafetyLittelfuse_5x20mm-IEC-Fuse-Cap-Marking_guide.pdf


Can the fuse voltage exceed the application voltage?

Yes - Fuses are designed for use in circuits at any voltage as long as they don't exceed the fuse's maximum voltage rating. (Exception - medium-voltage fuses from 2,400 to 38,000 volts may only be used at the voltages designated on the fuse's label) The voltage rating of a fuse is a safety rating that should never be exceeded.


How should I select the proper fuse amperage when I know the circuit amperage?

Always follow NEC guidelines for applying low-voltage fuses. Generally, the MINIMUM fuse size should be based on 125% of the circuits full load current. 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.


Why is the interrupting rating important?

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.


Do fuseholders require derating?

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.

Fuseholder Rerating

Fuseholder Reratingfuseholder_rerating.pdf


Does Littelfuse offer Class L fuseblocks?

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.


What is the purpose of fuseblock's rejection feature?

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.


Will Class CC fuses fit in Midget fuseholders?

Yes - Class CC fuses will fit into Midget fuseholders however Midget fuses will NOT fit into a Class CC holder due to the block's rejection feature.


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.

Fuseholder Cross ReferenceLittelfuse_fuseholder_cross-reference.pdf


Does Littelfuse have any legal disclaimers or notices about information on www.littelfuse.com?

Yes, Please read the following Legal Disclaimer for www.littelfuse.com.

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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.


What is the meaning for the different color bands around the PICO II 255/266 Series?

The PICO II 256/266 series was originally introduced with color coded bands on the part to denote current rating but has been replaced with the 251/253 series which has the amp rating laser marked on the epoxy. Littelfuse still offers the color coded 256/266 series for those customers that either cannot afford to design in the replacement part or prefer to use the banded product. The attached datasheet explains the color coding system.

PICO II (R) Very Fast-Acting 255/256 Series

PICO II255catalog.pdf


Do you have an explanation for your part number nomenclature?

Please See attached document for explanation of fuse part numbers.

PICO IILittelfuse Part Number Explanation


Does Littelfuse offer an In-Line fuseholder rated at 120VAC?

The only 120VAC In-Line Fuseholder we offer is the LEB series that holds a Midget or CC class fuse. 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 155 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.


Does Littelfuse offer fuse dummies?

Yes - Littelfuse offers dummy fuses for Midget style fuses (LNNB series).


Are fuse reducers available for Class T fuses?

No, fuse reducers are not available for Class T fuses.


What is the difference between Littelfuse's IDSR and FLSR ID Class RK5 fuses?

The difference is that the IDSR fuse series is the only Indicating Class RK5 fuse that is rated for 600VDC and 600VAC operation. The FLSR_ID fuse has a DC rating of 300VDC. Both the IDSR and FLSR_ID are also MSHA approved.


What is the difference between UL Class RK1 and RK5 fuses?

Class RK1 and RK5 fuses are the same physical size but Class RK1 fuses are more current-limiting than Class RK5 fuses. RK1 fuses can provide better protection because they allow less damaging energy to pass through them while opening (blowing).


Which fuse class offers better time delay?

Class RK5, RK1, and J fuses offer the most amount of time-delay. These fuses are required by UL (Underwriters Laboratories) to have a minimum of 10 seconds time delay at 500% of the fuse's rating.


Does Littelfuse have a privacy policy for www.littelfuse.com?

Yes. Please read the following:

This web site is the responsibility of Littelfuse, Inc. ("Littelfuse"). Littelfuse can be contacted by mail at 8755 West Higgins Road Suite 500, Chicago, IL, 60631 USA, by phone at 773-628-1000 or by e-mail at legal@littelfuse.com. The web server on which this web site is housed, owned and maintained by Littelfuse, Inc. The following policies apply to www.littelfuse.com.

1. Collection of Personal Information from Site Users

Littelfuse automatically collects and/or tracks (1) the home server domain names, type of computer and type of web browser of users of Littelfuse's web site, (2) the e-mail addresses of users that communicate with Littelfuse via e-mail, (3) information knowingly provided by the user in online forms, registration forms and surveys and (4) user-specific information on what pages users access.

Littelfuse collects information you voluntarily agree to provide us through the forms provided on the web site. Information collected includes limited personal data: your name, company name, address, telephone number, facsimile number and e-mail address.

Littelfuse does not place Internet cookies on users' hard drives.

When a user performs a search on Littelfuse's search engine, Littelfuse records information identifying the user or linking the user to the search performed. As necessary to provide services, Littelfuse does record limited information for every search request.

2. Use of Personal Data Collected

If you contact Littelfuse or voluntarily provide information to us, personal data collected by Littelfuse may be used by Littelfuse for editorial and feedback purposes, for marketing and promotional purposes, for a statistical analysis of users' behavior, for product development, for content improvement, to inform advertisers as to how many users have seen or clicked on their advertisements, and to customize content and layout of Littelfuse's site. Data on users' home servers is aggregated for internal review and then discarded. Names, postal and e-mail addresses, and phone numbers collected may be added to Littelfuse's databases and used for future calls and mailings regarding site updates, new products and services, upcoming events.

3. Disclosure of Personal Data to Third Parties

No personally identifying information will be shared with third parties. We do not sell, trade, or rent the personal information that you provide.

4. Opt-Out Page

Users may opt out of having their personal information collected by Littelfuse, used by Littelfuse for secondary purposes or used by Littelfuse to send promotional communications to the user, by contacting legal@littelfuse.com.

5. Access to and Ability to Correct Personal Data

Upon request via e-mail to legal@littelfuse.com, Littelfuse will provide to users a summary of any personal information retained by Littelfuse regarding the user. Users may modify, correct, change, or update their personal record or cause their personal record to be removed from Littelfuse's database. Littelfuse will only send personal records to the e-mail address on file for the user name associated with it.

6. Collection of Personal Data from Children

Littelfuse's web site is not intended for or marketed to persons under the age of 13.

7. Littelfuse's Right to Contact User

Littelfuse reserves the right to contact site users regarding its privacy policy, or any other policies or agreements relevant to site users.

8. Littelfuse's Right to Change Privacy Policy

Littelfuse reserves the right to change this policy at any time by posting a new privacy policy at this location. Please check this policy from time to time for changes.

 

Does Littelfuse have a quality policy?

Yes, Littelfuse strives to continuously improve quality and deliver world class products to our customers around the globe. Please see the attached pdf that contains the Littelfuse Quality Policy.

Littelfuse Quality Policy

Quality PolicyQuality_Policy.pdf


How can you find out what the UL rating would be for an IEC rated fuse (i.e. How can you convert the IEC rating to UL)?

The standard way to do this is to multiply the IEC rating by 1.43 times. This is a good approximation to the UL rating. It gets the customer in the ballpark. The conversion factor is applied to either the UL or IEC fuse rating to arrive at the other rating. The formula is 1.43 X (IEC rating) = (UL rating)


Do you have fuses that can be used in "NEC Class 1 Division 2"?

In regards to fuse protection of motors, appliances and lamps in Class 1 Div 2 Locations (Groups A-D), Section 501.115(B)(3) of the 2005 National Electrical Code states that fuses can be used within general-purpose enclosures if they are a nonindicating, filled, current limiting type. This letter is to inform you that the following fuses are a nonindicating, filled and current limiting type, which meets the requirements of NEC section 501.115(B)(3).

Class CC
CCMR 2/10 through 30A
KLKR 1-½ through 30A
KLDR 1/10 through 30A

Class RK1
LLNRK 1/10 through 600A
LLSRK 35 through 600A
KLNR 1 through 600A
KLSR 1 through 600A

Class RK5
FLNR 1/10 through 600A
FLSR 1/10 through 600A

Class L
KLPC 601 through 6000A
KLLU 601 through 4000A

Class T
JLLN 1 through 1200A
JLLS 1 through 800A

Class J
JLS 1 through 600A
JTD 1 through 600A

Class G
SLC ½ through 60A

The attached document provides additional information for your reference.

NEC Class 1 Div 2 Fuses

NEC Class 1 Div 2 FusesLittelfuse Fuses NEC Class 1 Division 2 c.pdf


What are the Littelfuse Terms and Conditions?

See the attached PDFs.

Littelfuse Terms and Conditions of Sale

Terms and Conditions of SaleLittelfuse-Standard-Terms-and-Conditions-of-Sales.pdf


What are the recommended storage conditions for fuses?

Littelfuse circuit protection components, their manufacturing processes and their packaging are designed for very long life.  There is no defined shelf life for our electrical products provided they have not been subjected to abnormal storage environments.  In order to minimize the aging process, it is important that the components are stored in their original packaging in proper storage conditions.  Littelfuse recommends storing products at <35°C and <65% relative humidity.  Under typical storage conditions, the product performance does not deteriorate.

Storage and Shelf LifeStorage-and-Shelf-Life.pdf


Do fuses have a shelf life?

Littelfuse circuit protection components, their manufacturing processes and their packaging are designed for very long life. There is no defined shelf life for our electrical products provided they have not been subjected to abnormal storage environments. In order to minimize the aging process, it is important that the components are stored in their original packaging in proper storage conditions. Littelfuse recommends storing products at <35°C and <65% relative humidity. Under typical storage conditions, the product performance does not deteriorate.

Storage and Shelf LifeStorage-and-Shelf-Life.pdf

Does altitude affect fuse performance?

Please see the attached file.

Altitude DeratingAltitude-Derating.pdf


Do high frequency applications affect fuse performance?

Please see the attached file.

High-Speed Fuse Applications - Frequency ConsiderationHigh-Speed-Fuse-Applications-Frequency-Consideration.pdf


Can you explain your date code format?

Please see the attached file.

Date Code Format IBUDate-Code-Format-IBU.pdf


What are UL fuse class and standards?

Please see the attached file.

UL Class Descriptions & ApplicationsUL-Class-Descriptions-&-Applications.pdf


Is the voltage rating that is printed on a fuseblock or fuseholder applicable for AC or DC voltage?

Per UL 4248-1 section 5.1.3.1, the voltage and current rating of a fuseholder are equal to or greater than the rating of the fuse that it accepts. AC testing is required and is also considered to cover the DC rating of the same value.


Why is voltage present in the indicating fuse holder when no fuse is installed?

Please see the attached file.

Voltage Present with Empty Indicating FuseblockVoltage-Present-with-Empty-Indicating-Fuseblock.pdf