Slow-blow fuses, also known as time-delay fuses or time-lag fuses, are a type of electrical protection device designed to withstand temporary overcurrent conditions without immediately blowing or opening the circuit. They are different from fast-acting (fast-blow) fuses, which will quickly open the circuit in response to any overcurrent.

Slow-blow fuses are typically identified by a special marking or colour code to distinguish them from fast-blow fuses. It's crucial to use the correct type of fuse for your specific application to ensure safety and proper circuit protection.

Key Features of Slow-Blow fuses include:

• Time Delay - slow-blow fuses are engineered to tolerate short-term overcurrent conditions that can occur during power-up or when certain electrical devices, such as motors or transformers, start. They allow these temporary surges to pass without immediately interrupting the circuit.
• High Inrush Current - some electrical devices, when powered on, can draw a high inrush current for a moment before settling into their normal operating current. Slow-blow fuses are designed to handle this inrush current without blowing.
• Overcurrent Protection - while slow-blow fuses offer time delay, they still provide protection against prolonged overcurrent conditions, such as a sustained short circuit. If the overcurrent persists for an extended period, the fuse will eventually open to protect the circuit.

These fuses are commonly used in applications where momentary overcurrent’s are expected but should not cause nuisance tripping or unnecessary interruptions. Some examples of applications that may use slow-blow fuses include electric motors, transformers, power supplies, and electronic devices with capacitors that require time to charge during startup.