The three families at a glance
| MCB | MCCB | ACB | |
|---|---|---|---|
| Typical rated current | up to 125 A | about 16 A to 1600 A | about 630 A to 6300 A |
| Breaking capacity | usually 6 or 10 kA (some higher) | usually 25 to 150 kA | very high, with a short-time withstand rating (Icw) |
| Trip settings | fixed (curve B, C or D) | fixed or adjustable; thermal-magnetic or electronic | electronic, fully adjustable (long time, short time, instantaneous, earth fault) |
| Where it is used | final circuits: lighting, sockets, small loads | feeders, sub-main boards, motor feeders | main incomers and large feeders in LV switchboards |
| Standard | IEC 60898-1 (household and similar) or IEC 60947-2 | IEC 60947-2 | IEC 60947-2 |
Step 1: the rated current (In)
Start from the design current of the circuit (Ib). The breaker rating must sit between the load and what the cable can carry: Ib ≤ In ≤ Iz, where Iz is the cable's current-carrying capacity after correction for installation method, grouping and ambient temperature (IEC 60364-4-43).
In Saudi Arabia, ambient temperature matters. MCBs are calibrated at 30 °C under IEC 60898-1 and MCCBs usually at 40 °C; inside a hot panel or an outdoor enclosure in summer, check the maker's derating table, or the breaker can trip below its nameplate rating.
Step 2: the breaking capacity
The breaker must interrupt the largest fault current that can flow where it is installed. Its breaking capacity (Icn for IEC 60898-1, Icu for IEC 60947-2) must be at least the prospective short-circuit current at that point. Close to a large transformer this can be tens of kiloamperes, so a 6 kA MCB that is fine in a villa may be unsafe in a factory main board. Ask your designer for the fault level, or send us the transformer size and cable lengths with your enquiry.
Step 3: the trip curve (MCB)
- Curve B (instant trip at 3 to 5 × In): resistive loads and long cable runs, where fault currents are low.
- Curve C (5 to 10 × In): general circuits, lighting with drivers, small motors. The most common choice.
- Curve D (10 to 20 × In): high inrush loads such as transformers, welding sets and motors that start direct on line.
For motors, a motor protection circuit breaker or an MCCB with a motor trip unit usually protects better than a plain MCB.
Step 4: poles and earth leakage
Choose 1P, 1P+N, 2P, 3P or 4P from the supply system and whether the neutral must be switched. For protection against electric shock, add residual current protection: 30 mA RCDs or RCBOs for socket circuits and wet areas, and 100 or 300 mA devices where fire protection is the aim (IEC 61008-1 and IEC 61009-1).
Step 5: selectivity with the upstream breaker
When a fault happens, only the breaker nearest to it should trip. Makers publish selectivity (discrimination) tables between their own breakers; use them when you mix MCBs under an MCCB, or MCCBs under an ACB. Buying both levels from the same range makes this easier to guarantee.
What to send us for a quotation
Rated current, number of poles, breaking capacity (kA), trip curve or trip unit, voltage, mounting (DIN rail, plug-in, fixed or draw-out) and the preferred brand. If you only have an old breaker, a clear photo of its nameplate is enough: we identify it and offer the same model or an approved equivalent.
Common questions
Can I use an MCB instead of an MCCB?
Only when the circuit needs 125 A or less and the MCB breaking capacity is at least the fault current where it will be installed. Above that, or where adjustable settings and selectivity matter, use an MCCB.
What does 10 kA on a breaker mean?
It is the breaking capacity: the largest short-circuit current the breaker can interrupt safely. It must be equal to or higher than the prospective fault current at the point of installation.
What is the difference between curves B, C and D?
They set how quickly the breaker trips on high current: B at 3 to 5 times the rating, C at 5 to 10 times, D at 10 to 20 times. Use C for general circuits and D for loads with a high starting current.
Need these items? Send your list or a nameplate photo; your quotation arrives within 24 hours.
This guide is general information. Final selection must follow the project design, the applicable standards and the maker's data.