Fuse Classes, Markings and Holder Compatibility
Compare common North American fuse classes and read voltage, current, interrupting, and time-response markings before checking the exact fuse and holder.
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Common class families
A fuse class identifies a standardized family with particular rating and construction requirements. It does not by itself supply every application limit or make all members of that class identical. Use the exact fuse and holder documentation.
| Class | Recognition context | What must still be checked |
|---|---|---|
| CC | Compact rejection-type branch-circuit fuse family | Voltage, current, holder, and the particular time-response characteristic. |
| J | A branch-circuit family with its own dimensions and performance requirements | Product time response and the correct Class J holder. |
| RK1 | A Class R rejection family | The manufacturer’s current-limiting and time-current data for the exact product. |
| RK5 | Another Class R rejection family | Do not assume performance identical to RK1 just because a holder arrangement appears similar. |
| T | Compact current-limiting branch-circuit family | Correct voltage version, dimensions, holder, and documented response. |
| L | A large-ampere low-voltage fuse family | Application voltage, mounting, equipment instructions, and specified rating. |
| G | A distinct branch-circuit fuse family | Specified holder, size/rating range, and application. |
| H / legacy installations | An identification requiring care with older equipment | Do not infer modern current-limiting performance or approve an upgrade without equipment review. |
This is an identification table, not a replacement matrix. Specialty semiconductor, photovoltaic, medium-voltage, automotive, and other fuse systems need their own documented criteria.
Read the complete fuse marking
- Ampere rating
- The marked current rating, not an automatic conductor or motor protection selection.
- AC / DC voltage rating
- A stated voltage application. An AC marking does not establish a DC rating.
- Interrupting rating
- The stated capability under the documented conditions; separate from normal load current.
- Time response and product series
- Use the actual time-current and let-through information. A class name alone is not a complete delay specification.
- Class and dimensions
- Identify the correct physical and listed family. Physical fit does not settle the electrical application.
Record all these fields with the complete catalog number and manufacturer. When coordination or equipment protection matters, retain the referenced curve and the conditions used to interpret it.
Check the holder and application
- Read the equipment’s specified fuse requirements and the holder’s class, voltage, and current information.
- Identify the installed fuse and proposed replacement by full catalog number.
- Compare voltage application, interrupting requirements, dimensions, time response, and any equipment-specific series/coordination conditions.
- Resolve a missing label or conflicting requirement before replacement; do not treat an available fuse as an approved substitute.
Use the standard ampere-rating reference for its separate lookup task and the breaker marking guide for breaker-specific information. This page does not select a fuse, establish selective coordination, or determine an assembly SCCR.