0673.800DRT4

FAQFrequently Asked Questions

• Is the Littelfuse 0673.800DRT4 suitable for protecting a power input that has high inrush current at startup? The Littelfuse 0673.800DRT4 is a slow-blow 800 mA fuse, so it can tolerate short inrush events better than a fast-acting fuse of the same rating. It is commonly used where capacitive input charging, transformer magnetizing current, or brief motor startup current would otherwise cause nuisance opening. For the Littelfuse 0673.800DRT4, confirm that the inrush profile stays below the fuse's time-current curve and that repeated surges do not create cumulative thermal stress.
• Can I use the Littelfuse 0673.800DRT4 in a 250 V AC/DC circuit, and what should I check before doing so? The Littelfuse 0673.800DRT4 is rated for 250 V AC and is listed for AC/DC use in its description, but DC applications need more review than AC because arc extinction is harder at higher DC voltages and available fault current can differ. For the Littelfuse 0673.800DRT4, verify that the circuit voltage, prospective short-circuit current, and the downstream protection architecture stay within the fuse's 50 A breaking capacity and system fault conditions.
• What PCB or leaded assembly constraints should I consider when replacing another axial fuse with the Littelfuse 0673.800DRT4? The Littelfuse 0673.800DRT4 uses a non-standard axial cartridge format, so the replacement needs to match lead spacing, body length, and the mechanical support strategy on the PCB. Because the body is about 3.90 mm by 11.00 mm, check clearance to adjacent components, solder joint strain relief, and whether the fuse is exposed to vibration or board flexing. A footprint that fits the part electrically can still fail mechanically if the axial mounting is not supported well.
• Is the Littelfuse 0673.800DRT4 appropriate for replacing a fast-acting 800 mA fuse? The Littelfuse 0673.800DRT4 is a slow-blow device, so it is not a like-for-like replacement for a fast-acting fuse in a circuit where rapid fault isolation is needed. If the original fuse was chosen to protect semiconductors or sensitive downstream traces from short overloads, the slower clearing behavior can change the protection profile. Use the Littelfuse 0673.800DRT4 only when the circuit can tolerate its time-delay response and the coordination with the rest of the protection chain still makes sense.
• How do I decide whether the Littelfuse 0673.800DRT4 is a good fit for transformer secondary protection? The Littelfuse 0673.800DRT4 can be a reasonable choice for transformer secondary protection when startup magnetizing current would otherwise open a fast fuse. The key checks are steady-state secondary current, expected overload duration, ambient temperature inside the enclosure, and whether the fault current available on the secondary side exceeds the fuse's interrupt rating. If the transformer runs hot or the enclosure is poorly ventilated, the effective margin can narrow.
• What are the practical differences between the Littelfuse 0673.800DRT4 and the substitute 0875.800MRET1P? The Littelfuse 0673.800DRT4 and 0875.800MRET1P are both 800 mA class fuses, but they may differ in package style, time-delay behavior, dimensions, approvals, and mounting compatibility. Before swapping one for the other, compare body size, lead form, breaking capacity, resistance, and whether the substitute preserves the same response profile under surge conditions. A part-number match on current rating alone does not guarantee a safe or drop-in replacement.
• Can the Littelfuse 0673.800DRT4 be used in equipment that runs continuously for long periods in a warm enclosure? Yes, but the Littelfuse 0673.800DRT4 should be derated with the actual ambient temperature and enclosure heat rise in mind, because fuse carrying capability shifts as the thermal environment changes. Continuous operation near the 800 mA rating in a warm enclosure can reduce margin, especially if nearby components raise local board temperature. For long-life industrial use, it is common to validate the fuse against worst-case ambient, airflow, and load tolerance rather than nominal room conditions.
• Does the Littelfuse 0673.800DRT4 provide enough interrupting capability for mains-side faults in all designs? Not necessarily. The Littelfuse 0673.800DRT4 has a breaking capacity of 50 A at rated voltage, which may be adequate in lower-energy secondary circuits but may be too low for some mains-fed designs with higher prospective fault current. The actual suitability depends on source impedance, transformer contribution, and the highest short-circuit current the system can deliver. In circuits with robust mains fault current, confirm that upstream protection or impedance limits the fault energy to within the fuse's interruption capability.
• What design changes are usually needed when migrating a board from a fast fuse to the Littelfuse 0673.800DRT4? When migrating to the Littelfuse 0673.800DRT4, engineers usually re-check the startup transient, overload coordination, and fault-clearing time because the slow-blow characteristic can let certain events persist longer. That can affect trace sizing, connector heating, semiconductor survivability, and whether upstream breakers or PTC devices coordinate correctly. It is common to revalidate with worst-case surge and fault tests instead of assuming the old protection margin still applies.
• Is the Littelfuse 0673.800DRT4 suitable for protecting low-voltage electronics, such as control boards or instrumentation? The Littelfuse 0673.800DRT4 can fit low-voltage electronics if the operating current and surge profile align with an 800 mA time-delay fuse, but it is not automatically the best choice for sensitive electronics. If downstream parts can fail from brief overloads, a slower fuse may not react quickly enough to limit damage. It tends to work better where nuisance trips are a bigger issue than ultra-fast fault isolation, such as small power supplies, instrument mains inputs, and some mixed-signal control assemblies.
• What should I verify before approving the Littelfuse 0673.800DRT4 for a production design with UL or CSA requirements? The Littelfuse 0673.800DRT4 already carries UL and CSA approval listings, but the final product still needs system-level compliance verification. Check that the fuse is used within its rated voltage, current, mounting method, and fault conditions, and confirm the completed assembly meets the applicable end-product standard. Approval on the component does not replace enclosure, spacing, thermal, and abnormal-operation testing at the system level.
• Are there reliability concerns if I use the Littelfuse 0673.800DRT4 in a vibration-prone or field-serviceable product? The Littelfuse 0673.800DRT4 is a through-hole axial cartridge, which is generally easier to retain mechanically than some ultra-compact fuse styles, but vibration and repeated handling still matter. In field-serviceable equipment, check lead support, solder joint fatigue, and whether replacement access could encourage incorrect part substitution. For vibration-prone designs, mechanical retention and PCB anchoring are part of the reliability picture, not just the fuse rating itself.