Overview
The Littelfuse FLSR-4-ID is a Class RK5 dual-element time-delay indicator fuse rated for 600VAC (300VDC) at 4 amps. Part of Littelfuse’s FLSR_ID series, this fuse combines proven overload and short-circuit protection with a patented visual indicator that signals blown-fuse status at a glance—critical for minimizing production downtime in industrial control cabinets, motor branch circuits, and switchboard applications.
Key Features
- Dual-Element Design: Provides advanced protection against both short circuits and overload conditions with precision time-delay characteristics suitable for inductive loads and motors.
- Visual Blown-Fuse Indicator: Patented solid-state indicator shows fuse status instantly, eliminating guesswork and reducing troubleshooting time on the plant floor.
- Class RK5 Rating: UL-listed Class RK5 rejection fuse; meets ANSI Standard 248-12, CSA certification, and Federal Specification WF-1814 (QPL-W-F-1814).
- High Interrupting Capacity: 200 kA at 600VAC (symmetrical) breaks faults cleanly and safely without nuisance interruptions on transient inrush currents.
- Cartridge Terminal: 13/16″ diameter × 5″ length ferrule-type terminals fit standard RK5 fuse holders; reliable contact and secure installation.
Technical Specifications
| Voltage Rating | 600VAC / 300VDC |
| Ampere Rating | 4 A |
| Fuse Class | Class RK5 |
| Time Delay Type | Dual Element, Slo-Blo (T-Type) |
| Interrupting Rating | 200 kA at 600VAC (symmetrical), 20 kA at 300VDC |
| Indicator Feature | Visual blown-fuse indicator (Indicator™ series) |
| Terminal Type | Cartridge, Ferrule (13/16″ × 5″) |
| UL Classification | Class RK5, UL Listed |
| Standards | ANSI 248-12, CSA Certified, Federal Specification WF-1814 |
| Application Types | Motors, transformers, switchboard feeders, motor control centers, general-purpose circuits |
| Series | POWR-PRO FLSR_ID |
Typical Applications
- Motor Protection: Branch circuits feeding 1–3 HP AC induction motors with soft-start or VFD devices; time-delay characteristic tolerates motor inrush without nuisance trips.
- Transformer Primary/Secondary: Feed protection for control transformers, distribution transformers, and UPS systems rated 600V.
- Switchboard & Panelboard Mains: Service entrance and main feeder protection in industrial control cabinets and MCC (Motor Control Center) applications.
- Maintenance Efficiency: Visual indicator eliminates need to meter or replace suspected fuses blindly, reducing maintenance time and improving safety compliance.
Compatibility & Replacements
Compatible With
- Standard Class RK5 fuse holders and rejection-type fuse blocks rated for 600VAC/300VDC.
- Industrial control panels, motor control centers (MCC), and disconnect switches with ferrule-cartridge fuse sockets.
- Power distribution equipment, transformers, and switchgear requiring Class RK5 dual-element time-delay protection.
- Motor branch circuits and feeder protection in industrial automation systems.
Replaces / Drop-In Replacement For
- Littelfuse FLSR-4 (non-indicator version) — upgrade to FLSR-4-ID for visual status indication.
- Other Class RK5 4A fuses rated 600VAC — confirm your holder is a rejection-type RK5 socket before substitution.
Works With
- Class RK5 rejection fuse holders and clips (ferrule cartridge sockets).
- 600VAC/300VDC industrial distribution systems and control circuits.
- Time-delay protective schemes for motors, transformers, and inductive loads.
- Safety interlocks and maintenance protocols requiring visible blown-fuse indication.
