How are fuses sized?

• A. By material
• B. By current and voltage rating
• C. By length
• D. By color

Answer: (B)

Sizing a fuse means choosing its current rating and its voltage rating. The current rating tells you the maximum continuous current the fuse can carry; you pick one just above the circuit’s normal operating current so the fuse stays closed under normal use but opens if a fault pushes current higher than what the conductors and components can safely handle. The voltage rating indicates the maximum voltage the fuse can interrupt safely; it must be at least the system voltage to prevent arcing or failure to open when a fault occurs. Time behavior matters too in cases with inrush or surge—some loads need a fast-acting fuse, while others work with a slow-blow type to tolerate temporary spikes. Length, color, or material don’t determine the protection level; they relate to construction or appearance, not how the fuse protects the circuit.