Glass tube · 5 × 20 mmNickel-plated end capsFuse wire (melts) · T2A: slow-blow 2 AT2AL250V marking

Transparent glass tube, two metal caps and a thin fuse wire inside
Tube and caps ≈ Ø 5 × 20 mm; with a matching fuse holder

Protection parts

Glass fuse (5×20 mm)

In simple terms

What is this?

The deliberately weak link of the circuit. When too much current arrives, its thin wire melts and breaks the chain; the remaining parts are saved.

What is it for?

Opens the circuit on overcurrent and protects the wire and parts from burning; single use.

Where do you see it?

In the current input of a multimeter, and inside some adapters and devices.

How do you spot it?

Clear glass tube with a metal cap at each end and a thin wire inside; its current and voltage ratings are printed on it.

Caution:

Never replace a blown fuse with one for a higher current; nothing would protect the wire anymore.

Technical definition

The thin metal wire inside the glass tube melts and opens the circuit when enough overcurrent flows for a certain time. It is single-use and is connected in series with the line to be protected. F is fast, T is time-delay; the choice depends not only on the current but also on the trip time, voltage and breaking capacity.

Size5 × 20 mm

Example current1 A

TypeF fast · T time-delay

Schematic symbol IEC and ANSI differ

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2

1Cap 1Series input on the line to protect; non-polarized1

2Cap 2Series output to the load; non-polarized2

Features typical

Size: 5 × 20 mm
Rated current: 1 A example; chosen by the load
Speed: F fast · T time-delay
Voltage: Example marked 250 V; the DC rating is verified separately
I²t: Integral of the current squared over time, A²s; depends on the series
Breaking capacity: Depends on the series and the AC/DC condition
Replacement: When it blows, replace it with the same value and type
Example part: F1A 250 V or T1A 250 V, 5×20 mm glass fuse

Common mistakes

Fitting a larger fuseFitting a larger value without finding the fault removes the protection; never bridge it with wire.

Expecting it to open instantly at the rated currentThe time-current curve sets the trip time. A T type tolerates inrush surges longer.

Looking only at the ampere ratingThe F/T type, I²t, voltage and breaking capacity must also be suitable. The Lab uses low-voltage circuits only.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

Protecting the supply lineMultimeter current inputChoosing F/T by the inrush surge

Try it in the Lab