Moulded-case circuit breaker (MCCB) versus miniature circuit breaker (MCB)

In the main distribution board of a large processing hall or horticultural business, two types of breakers are often found side by side: small miniature circuit breakers (MCBs, see the B/C/D characteristics guide) for final circuits, and a larger moulded-case circuit breaker (MCCB) on the main supply or large sub-distribution boards. Although both look like "a breaker," they fall under different standards with a different target group and a different performance rating.

Two different standards, two target groups

• IEC 60898-1 (MCB, miniature circuit breaker) is intended for low-voltage installations operated (in part) by ordinary persons — think of a regular consumer unit. MCBs are standardised up to a maximum rated current of 125A.
• IEC 60947-2 (MCCB and circuit breakers in the broader sense) is intended for low-voltage switchgear and controlgear assemblies that are selected, installed and maintained by instructed or skilled persons — with a rated-current range extending up to 6300A.

Short-circuit withstand: a different rating, not a 1-to-1 comparison

This is a crucial difference that is often overlooked:

• Under IEC 60898-1 (MCB), short-circuit withstand capability is indicated as Icn (rated short-circuit capacity) — a single value, typically in the range of 6 to 10 kA.
• Under IEC 60947-2 (MCCB), short-circuit withstand capability is expressed as a combination of Icu (ultimate short-circuit breaking capacity) and Ics (service short-circuit breaking capacity, a percentage of Icu) — with Icu values that can reach up to 150 kA.

Icn (IEC 60898-1) and Icu/Ics (IEC 60947-2) are not simply interchangeable as comparison figures — they are tested according to different test criteria within their own standard. Two breakers that look visually similar can therefore have substantially different performance guarantees.

Note: the exact Icu/Ics or Icn value for a specific make/type follows from that product's own rating plate/product documentation — this article explains the classification principle, not a universal figure per breaker type.

Why this matters for replacement/inspection

Replacing a moulded-case circuit breaker (MCCB) on a main supply with a miniature circuit breaker (MCB) — or conversely, applying an MCB at a position where the standard requires an MCCB — is problematic: besides the performance difference in short-circuit withstand capability, IEC 60898-1 explicitly does not apply to applications operated by ordinary persons at the moulded-case circuit breaker level. During a NEN 3140 inspection, the breaker used must therefore match both the power/short-circuit current at that position and the intended user group.

Common mistakes

1. Treating Icn (MCB) and Icu (MCCB) as directly comparable figures when assessing whether a breaker is "heavy-duty enough" — these are different test standards with a different meaning.
2. Replacing an MCCB with an MCB "because the rated current matches", without checking whether the short-circuit withstand capability at that position in the installation is still sufficient.
3. Assuming that every breaker in the distribution board falls under the same standard — in practice, the main supply (often MCCB, IEC 60947-2) and final circuits (often MCB, IEC 60898-1) exist side by side in the same installation, each with its own application logic.

Related

• Circuit breaker characteristics B, C and D
• Distribution boards and selectivity