## FNQ-R-7: Technical Overview The **FNQ-R-7** is a high-performance, time-delay fuse belonging to the **Limitron™** family, manufactured by **Bussmann (Eaton)**. It is specifically designed as a "CC Class" fuse, which is one of the most common standards for branch circuit protection in industrial environments. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Model Number** | FNQ-R-7 | | **Amperage Rating** | 7 Amps | | **Voltage Rating (AC)** | 600 Vac (or less) | | **Interrupting Rating** | 200,000 Amps RMS Symmetrical | | **Fuse Class** | Class CC | | **Response Characteristic** | Time-Delay (Slow Blow) | | **Physical Dimensions** | 13/32" x 1-1/2" (10.3 x 38.1 mm) | | **Material** | Melamine tube with nickel-plated brass endcaps | --- ### 2. Electronic Characteristics & Functionality #### A. Rejection Feature The "R" in the part number denotes a **rejection tip**. Class CC fuses have a unique physical groove on one end. This ensures that: * Standard non-rejection fuses cannot be inserted into a Class CC holder. * The circuit is guaranteed the high interrupting rating and protection level intended by the design. #### B. Time-Delay Mechanism Unlike "Fast-Acting" fuses, the FNQ-R-7 is engineered to withstand short-duration **inrush currents**. * **Inductive Loads:** It is ideal for small motors and transformers that pull a high surge of current upon startup. * **Nuisance Tripping:** It prevents the fuse from blowing during normal operational spikes while still protecting against sustained overloads and short circuits. #### C. High Current Limitation The FNQ-R-7 is highly current-limiting. In the event of a catastrophic short circuit, it reacts in less than half a cycle to "cut off" the peak current, protecting sensitive downstream components like contactors or solid-state relays. --- ### 3. Common Applications The FNQ-R-7 is typically found in industrial control panels and machinery. Primary use cases include: 1. **Control Transformers:** Protecting the primary side of industrial control transformers. 2. **Solanoids:** Handling the inductive kickback and startup draw. 3. **Small Motor Branch Circuits:** Providing specialized protection where space is limited but high interrupting capacity is required. --- ### 4. Comparison to Similar Fuses | Fuse Type | Characteristic | Best For | | :--- | :--- | :--- | | **FNQ (Midget)** | Supplemental, Time-Delay | General purpose, no rejection tip. | | **FNQ-R (Class CC)** | Branch Circuit, Time-Delay | High safety requirements, motor/transformer protection. | | **KTK-R (Class CC)** | Fast-Acting | Resistive loads, lighting, no inrush current. |