Littelfuse LH250302SR

The following guidelines help simplify the selection of the correct fuse holder:

1. Determine the System Voltage Since fuses are selected based on system voltage, the fuse holder selection should match the voltage rating of the fuse.
2. Determine the Design Short-Circuit Current The available and/or design short-circuit current is an important consideration when determining the class of fuse and fuse holder to use. If the available short-circuit current cannot be determined, or if it varies with equipment location, then for maximum safety, a fuse with a 200,000 ampere interrupting rating (A.I.R.) and a matching fuse holder with a withstand rating of 200,000 amperes should be selected. Class H fuse holders accept Class H or K5 fuses (interrupting rating up to 50,000 amperes) as well as Class R fuses (interrupting rating of 200,000 A.I.R.). To prevent insertion of fuses with incorrect interrupting ratings, it is recommended to use Class R fuse holders with Class R fuses, and Class H fuse holders with Class H or K5 fuses. These fuse holders are identical in size, but Class R fuse holders have a rejection feature that only allows insertion of Class R fuses.
3. Determine the Type and Ampere Rating of the Fuse to Be Used In addition to the voltage and interrupting ratings mentioned above, the ampere rating, time-current characteristics (fast-acting or time-delay), and physical size of the fuse are other important considerations in fuse selection. Once the fuse type has been selected, the matching fuse holder can be chosen. Fuse holders are available in 30, 60, 100, 200, 400, and 600 ampere ratings and can be used with fuses of the corresponding ampere rating or lower. For example, a 30 ampere fuse holder can be used with fuses rated from 0 to 30 amperes.
4. Determine Whether NEC, CSA, UL, or Other Requirements Apply If the fuse holder is to be installed in equipment that requires agency certification, the relevant requirements should be obtained from the certifying agency before selecting the fuse and fuse holder.
5. Select the Wire Termination Type Three wire termination types are available: a) Screw — for use with spade terminals or ring terminals. b) Screw with pressure plate — for use with solid or stranded wire without terminals. Recommended where vibration is a factor. c) Box lug — most durable. For use with all types of solid wire and Class B and Class C stranded wire. Not suitable for welding cable or other rope-stranded conductors. 1/4-inch quick-connect terminals, rated up to 20A, are available for miniature and Class CC fuse holders.
6. Determine the Number of Poles per Fuse Holder The number of poles per fuse group is determined by the circuit characteristics. The option to combine individual fuse holders into ganged configurations will depend on available space and the type of wire used.
7. Determine Whether Reinforced Fuse Clips Are Required Fuse clips may lose some tension over time. This can be prevented by specifying reinforced fuse clips. Reinforced clips are standard on certain fuse holders (see individual product pages).

• Class H and Class R fuse holders feature clip-type design to maximize electrical contact and minimize temperature rise.
• All Class H fuse holders rated 100 amperes and above are standard-equipped with reinforced clips. Note: For reinforced clips on Class H fuse holders rated 30–60 amperes, add the suffix "R" after the connector type.
• All Class R fuse holders are standard-equipped with reinforced clips.