Mercury 5 x 20mm T1A Slow Blow Fuse - 250V IEC Certified

The Mercury T1A is a 5 x 20mm glass tube slow blow fuse rated at 1A continuous current and 250V, carrying IEC certification for use in consumer electronics, audio equipment, test instruments and similar mains-powered devices. The delay-action element inside the glass tube tolerates brief inrush currents during motor startup, capacitor charging and transformer energisation without breaking the circuit, then trips on sustained overcurrent or short-circuit conditions.

Designed for equipment with capacitive or inductive loads where a fast-blow fuse would cause nuisance tripping, the T1A handles transient current peaks that last a few milliseconds to a few hundred milliseconds before the element heats enough to melt. This makes it suitable for protecting power supplies, amplifiers, motors and other devices where normal operation includes short-duration current surges above the 1A steady-state rating.

The 5 x 20mm dimension is a standard metric fuse size found in IEC-compliant fuseholders on equipment sold across Europe and the UK. The glass tube construction allows visual inspection of the element without removing the fuse from the holder — a broken wire or darkened glass indicates a blown fuse. The nickel-plated brass end caps provide corrosion resistance and good electrical contact in standard panel-mount or PCB-mount fuseholders.

What's the difference between slow blow and fast blow?

A slow blow fuse has a thicker element or additional mass that takes longer to heat and melt under overcurrent. This delays tripping during brief startup surges that would immediately blow a fast-acting fuse. For sustained overcurrent or short-circuit conditions, both types eventually trip — the slow blow just gives a few hundred milliseconds of tolerance for transient peaks.

What does T1A mean?

The 'T' prefix indicates a time-delay (slow blow) characteristic. The '1A' is the nominal current rating — the fuse is designed to carry 1A continuously without tripping, and to trip on sustained currents above that threshold.

Can this replace a fast blow 1A fuse?

Only if the equipment is designed to accept a time-delay fuse. Substituting a slow blow for a fast blow reduces the speed of overcurrent protection, which may be unsafe in circuits requiring fast disconnection. Check the equipment manual or the original fuse marking before swapping fuse types.

How many fuses are in a pack?

Pack quantities vary. Check the product specification or contact Niori to confirm the quantity supplied with this SKU.