A fuse box has a series of threaded sockets into which the fuses are screwed in like light bulbs. Each circuit in the home is protected by a fuse, and each fuse must be the correct type and have an appropriate amperage rating for its circuit. Using the wrong type of fuse for a circuit can pose a serious fire hazard, so it’s important to identify the correct fuse for each circuit. The Edison base (Type T) looks like a light bulb base and fits the standard sockets found in old fuse boxes. Rejection base (Type S) fuses will work with Edison-type sockets only when combined with an adapter base that screws and locks into the Edison socket. The Type S fuse then screws into the adapter. Rejection bases are also known as “tamper-proof,” and they were developed to prevent homeowners from using the wrong type of fuse for a circuit. Each Type S fuse of a specific amperage rating has a matching base adapter with a specific size of thread that prevents mismatching the fuses. For example, it stops a person from putting a 20-amp fuse in a 15-amp circuit, a potentially serious mistake. This condition is called over-fusing and can result in the fuse failing to blow before the circuit wiring overheats and potentially catches fire. A 15-amp Type S fits only a 15-amp base adapter. By contrast, a Type T fuse can fit into any Edison socket, regardless of the circuit’s amperage. If you have an old fuse box with Edison sockets, switching to socket adapters and Type S fuses makes the panel much safer. These fuses are designed for use in general lighting and power circuits that do not contain electric motors. Electric motors draw additional current at startup and will blow a Type W fuse if the motor is of any significant size. Because of this, time-delay fuses are used much more commonly than type-W fuses. Type-W fuse rating: 120 volts; up to 30 amps SL and TL fuses contain a plug of heat-absorbing solder that’s attached to the center of the fuse element (the part that burns out, or blows, during a circuit overload). This allows the fuse to absorb a temporary circuit overload, such as that caused by a brief surge in power demand when a motor starts up. Without a time-delay feature, simply starting your garbage disposer or refrigerator would cause a fuse to blow. Type SL and TL fuse rating: 120 volts; up to 30 amps Heavy-duty time-delay fuses contain a spring-loaded metal fuse link attached to a solder plug. If the overloaded circuit condition continues for too long, the solder plug melts and the spring pulls the fuse link free, cutting power to the circuit. This allows the fuse to absorb a longer temporary circuit overload than with other time-delay fuses. Type S and T heavy-duty fuse rating: 120 volts; up to 30 amps Mini-breaker fuse rating: 120 volts; up to 20 amps
