What Is a Fuse?
A fuse is a single-use protection element that permanently cuts the circuit by melting when the current through it exceeds a certain value.
How Does It Work?
The thin metal wire inside it heats up above the rated current. If the current is excessive the wire melts and the circuit opens; so cables and components are protected from the fire or damage overcurrent would cause.
Rated Current and Voltage
Every fuse is referred to by a rated current (e.g. 1A, 5A) and voltage. It conducts continuously below the rated current; above it, it blows within a certain time. A value slightly above the circuit's normal current is chosen.
| Class | Behavior |
|---|---|
| Fast (F) | Blows immediately on a sudden overcurrent |
| Slow (T) | Withstands short pulses |
| Breaking cap. | Max current it safely interrupts |
Fast and Slow
A fast (F) fuse protects sensitive circuits against sudden current. A slow (T, slow-blow) fuse withstands, without blowing, the short current pulses at motor/capacitor startup.
Where Is It Used?
Power inputs, adapters, automotive, home appliances and the supply line of almost every electronic device as the first protection layer.
Other Protection Elements
A fuse doesn't work alone; there are complementary protection elements: the reusable circuit breaker against overcurrent, the thermal fuse against overtemperature, the gas discharge tube against high-energy surges and ESD protection against static discharge.
Common Mistakes
- Too high a value: a fuse larger than needed makes the protection useless.
- Breaking capacity: a fuse with low breaking capacity can explode at high fault current.
- Bridging: bridging a blown fuse with wire creates a fire risk.
Frequently Asked Questions
Why does a fuse blow?+
Can a blown fuse be reused?+
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