The **FNQ-R-20** is a specific type of high-performance industrial fuse. It belongs to the **Limitron™** family manufactured by Bussmann (a division of Eaton). Below is a detailed breakdown of its electronic and mechanical specifications. --- ## 1. Core Specifications The FNQ-R-20 is a **Class CC** current-limiting fuse. These are designed specifically for branch circuit protection and are physically rejected by non-Class CC fuse holders to ensure safety. | Feature | Specification | | :--- | :--- | | **Model Number** | FNQ-R-20 | | **Amperage Rating** | 20 Amps | | **Voltage Rating (AC)** | 600 Vac | | **Interrupting Rating** | 200,000 Amps RMS Symmetrical | | **Fuse Class** | Class CC | | **Response Characteristic** | Time-Delay (Slow-Blow) | | **Dimensions** | 13/32" x 1-1/2" (10.3 x 38.1 mm) | --- ## 2. Key Electronic Characteristics ### A. Time-Delay Functionality The FNQ-R-20 is a **Time-Delay** fuse. This means it can withstand temporary "inrush currents" (spikes) without blowing. * **Application:** Ideal for inductive loads like small motors and transformers that pull high current for a fraction of a second when starting up. * **Behavior:** It will hold at 200% of its rated load for a minimum of 12 seconds. ### B. Current Limiting As a Class CC fuse, it is "Current Limiting." In the event of a massive short circuit, the fuse reacts so quickly that it interrupts the current before it reaches its full peak magnitude. This protects downstream sensitive electronic components from thermal and magnetic stress. ### C. Rejection Feature The "R" in the model name stands for **Rejection**. The fuse has a unique physical "groove" on one end. * **Safety:** This prevents a user from accidentally replacing it with a lower-rated or non-current-limiting fuse (like a standard midget fuse), ensuring the circuit remains protected at the 200kA interrupting level. --- ## 3. Physical Construction The fuse is built to withstand harsh industrial environments: * **Body Material:** High-grade Melamine (fiberglass) tube for superior heat resistance and structural integrity. * **End Caps:** Nickel-plated brass for high conductivity and corrosion resistance. * **Internal Element:** A dual-element design that allows for the time-delay characteristic. --- ## 4. Typical Applications The FNQ-R-20 is most commonly found in: 1. **Control Transformers:** Protecting the primary side of the transformer. 2. **Motor Branch Circuits:** Providing short-circuit protection for small horsepower motors. 3. **Solenoids:** Handling the high-draw engagement phase of electromagnetic coils.