Blade Fuse (ATO / Mini / Maxi)
A family of fusible-element fuses with a plastic body and two blade legs, used in vehicles and low-voltage DC systems. They are made in Mini, standard ATO and Maxi sizes; the larger the size, the more current they carry. The amperage is colour-coded on the body: 10 A red, 15 A blue, 20 A yellow, 30 A green.
A blade fuse works by the metal strip inside it melting along a particular current-time curve. It opens after a long period slightly above its rated value, and within milliseconds far above it. This behaviour keeps the short high current at motor start-up from blowing the fuse unnecessarily.
The common current ranges are roughly as follows: Mini 2–30 A, standard ATO 1–40 A, Maxi 20–120 A. The body colour indicates the current rating and is largely standard across manufacturers.
Points to watch when selecting and fitting:
- Selection rule: the fuse protects the cable. The rating must stay below the current that the cable cross-section of that circuit can carry continuously, and above the normal operating current.
- Position: it is fitted as close to the battery terminal as possible; what is protected is the cable after the fuse.
- Holder quality: a loose holder creates contact resistance, heats up, causes voltage drop and can melt the holder. Check it by hand under load.
- Characteristic: because of its fast-blow construction it may trip needlessly on some motor start-ups; in that case a solution with a slow-blow characteristic should be used.
Replacing a fuse that keeps blowing with a larger one hides the fault and leaves the cable unprotected; in a vehicle or RV that means a fire risk. In installations exposed to water and damp, use a sealed fuse box; the oxide layer on the blade legs increases contact resistance over time. Since damp and vibration accelerate this degradation, the holders in the distribution panel should be inspected visually at regular intervals. On lines carrying 30 A and above continuously, a Maxi type or a bolt-down fuse is safer.
Context in which this term is used: Installation, redundancy and field continuity