Mercury 5A Quick Blow Fuse 5x20mm - 250V IEC Standard

The Mercury F5A is a 5A quick blow fuse in a standard 5x20mm glass tube body with nickel-plated end caps, rated for 250V AC/DC circuits. Quick blow fuses interrupt current within milliseconds of detecting an overcurrent condition, providing fast protection for sensitive electronics, small appliances and circuit boards where damage occurs rapidly under fault conditions.

Designed for use in mains-powered equipment, audio electronics, lighting controllers, power supplies and test equipment where the protected circuit draws up to 5A under normal operation. The 5x20mm format is one of the most common glass fuse sizes and fits standard panel-mount or PCB-mount fuse holders. The fuse breaks the circuit when current exceeds the 5A rating, preventing damage to downstream components.

The glass body allows visual inspection of the fuse element to confirm whether the fuse has blown without needing a multimeter. The nickel-plated brass end caps provide low contact resistance and resist corrosion in typical indoor environments. Mercury fuses are manufactured to IEC 60127 standards, ensuring consistent breaking capacity and dimensional compatibility with fuse holders from other manufacturers.

What is a quick blow fuse?

A quick blow (also called fast-acting or F-type) fuse interrupts the circuit within milliseconds of detecting overcurrent. This contrasts with slow-blow or time-delay fuses, which tolerate brief current surges before breaking. Quick blow fuses suit circuits with sensitive components that cannot survive even short overcurrent periods.

What's the difference between 5A and other ratings?

The 5A rating means the fuse will carry up to 5 amps continuously under normal conditions and will blow when current exceeds this threshold. Lower-rated fuses (1A, 2A, 3A) protect circuits with lower current draw; higher-rated fuses (10A, 15A) suit circuits with greater power demands. Always match the fuse rating to the protected circuit's maximum expected current.

Can this fuse be used in 230V UK mains circuits?

Yes, the 250V rating covers UK 230V mains. However, this 5A rating is typically too low for directly protecting mains appliances — it suits low-power equipment like LED drivers, audio amplifiers, control circuits and power supplies where the circuit draws under 5A.

How do I know if the fuse has blown?

The glass body allows you to see the thin wire element inside. If the fuse has blown, the wire will be visibly broken or the glass may show scorch marks. For confirmation, use a multimeter in continuity mode across the two end caps — a blown fuse shows no continuity.