Circuit breaker / MCB (C0,5, 1 pole) · Exterior view
Input screw (line)Operating lever (I on / O off)Curve and current: C0,5 (Lab) · 0.5 A, C curveOutput screw (load)
DIN rail housing, trip lever, C curve and rated current marking, and two screw terminals
DIN rail module ≈ 18 × 80 × 70 mm (depends on the series)
Protection parts

Circuit breaker / MCB (C0,5, 1 pole)

In simple terms
What is this?

A fuse that switches itself off and can be reset. When the load is too high the breaker trips, and you lift the lever.

What is it for?

Opens the circuit on overload or a short circuit; works again without a new part.

Where do you see it?

The rows of small breakers in the fuse box of a house.

How do you spot it?

Narrow rectangular body with a lever on the front; a current rating code made of letters and a number is printed on top.

Caution:

It does not protect against electric shock; do not experiment on the mains, examine it only at low voltage.

Technical definition

A single-pole miniature circuit breaker: it opens with a bimetal that heats up on overload and with an electromagnet on a high short-circuit current. A marking such as C0,5 means C curve and 0.5 A rated current; a common real-world example is C6 (6 A). The Lab uses low voltage only; real mains installation and wiring are outside the scope of this app.

Rated current (Lab)0,5 A (C0,5)
Polarity1P
Magnetic tripping5–10 × In
Schematic symbol IEC and ANSI differ
I>

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

Pins 2
1Line terminal 1Follow the manufacturer’s input direction; low voltage in the Lab1
2Load terminal 2Output of the protected line; series connection2
Features typical
Rated current (Lab)
0,5 A (C0,5)
Selectable rated current (Lab)
0.1 / 0.25 / 0.5 / 1 / 6 A
Magnetic tripping
5–10 × In; in the Lab model 5 × In and above (for C0,5: 2.5 A)
Thermal test
No tripping at 1.13 × In, tripping at 1.45 × In; 1-hour test
Thermal behavior
Depends on time, ambient temperature and preload
Real example: C6
6 A rated, magnetic tripping 30–60 A
Real example: voltage / breaking
230/400 V AC, 6 kA; depends on the series
DC use
Only with the manufacturer’s DC rating and wiring
Protection type
Overcurrent only; not residual-current (earth-leakage) protection
Re-arming
After the fault is cleared and the mechanism has cooled
Example part
Lab: C0,5, 1P; real example: C6, 1P, IEC 60898-1 class MCB
Common mistakes
Expecting it to trip instantly as soon as the rated current is exceededThermal tripping takes time on a small overload. The fast region of the C curve is 5–10 × In.
Mistaking it for residual-current protectionAn MCB does not replace a residual-current device against electric shock.
Trying it on the mainsLab uses only a low-voltage model. Do not work on a real 230 V installation; never re-arm before fixing the fault.

Test with a multimeter

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

Take a measurement
Where it is used
Comparing thermal and magnetic trippingLow-voltage protection modelComparing a fuse with a breaker
Related lessons
Find the short circuit
Module 6 · TroubleshootingsoonMeasuring current and the fuse
Module 2 · Measuring with a multimetersoon
Try it in the Lab