How to Choose an MCB: Rating, Tripping Curve, and Brand

In brief: the MCB rating is selected based on the line's cable cross-section rather than the appliance power rating – 10 A for 1.5 mm², 16 A for 2.5 mm², 25 A for 4 mm², 32 A for 6 mm², and 50 A for 10 mm². For residential applications, a Type C tripping characteristic is typically used, while Type B is suitable for lighting circuits and socket circuits without high inrush currents. The breaking capacity should be at least 6 kA for residential sectors, or higher depending on the calculated short-circuit current near the substation. You can select the appropriate rating for your circuit using the online calculator provided in this article.

Brand selection should be based on these technical parameters rather than brand recognition: two MCBs with identical ratings, tripping characteristics, and breaking capacities provide identical circuit protection. When choosing equipment, consider premium brands such as ABB, Schneider Electric, Legrand, Eaton, Hager, Siemens, or Schrack, which offer high-quality components meeting all EU standards.

Why do you need a miniature circuit breaker?

A miniature circuit breaker (MCB) is the primary device used to protect electrical circuits from overloads and short circuits. Selecting the correct MCB ensures the safety of the electrical installation and prevents damage to the wiring and connected equipment.

Rated current: how to determine it

The rated current of the MCB must correspond to the cable cross-section and the allowable load of the circuit. The fundamental rule is: the MCB protects the cable, not the consumers.

Cable cross-section, mm²	Allowable current, A	Recommended MCB
1.5	23	10 A
2.5	30	16 A
4.0	41	25 A
6.0	50	32 A
10.0	80	50 A

The allowable currents are provided for single copper conductors with PVC insulation installed in open air, in accordance with HD 60364-5-52. When installed in a conduit or concealed, the allowable current decreases (for example, for 1.5 mm² in a conduit, it is 19 A; for 2.5 mm², it is 25 A). The recommendations in the table include a safety margin and are suitable for various installation conditions. A higher rating (e.g., 16 A for a 1.5 mm² cable) is only permissible for open installation and only after verifying the allowable current for the actual installation conditions according to HD 60364-5-52.

You can select the required cross-section and MCB rating for your circuit using the calculator below.

Tripping characteristic: B, C, or D

The characteristic determines the level of short-term current excess at which the MCB will trip instantaneously:

• Type B (3–5 In) – for circuits without high inrush currents: lighting and socket circuits in residential dwellings. This is the most sensitive type, providing maximum protection for the wiring.
• Type C (5–10 In) – universal, for circuits with moderate inrush currents: air conditioners, pumps, and mixed loads. This is the most common choice.
• Type D (10–20 In) – for electric motors, transformers, and other equipment with high inrush currents.

For apartments and houses, Type C is suitable in most cases. Type B should be considered for lighting and socket lines if there are no heavy loads with significant inrush currents.

Types A, K, and Z are standardised for industrial devices under IEC 60947-2, but they can also be found in modular series—for example, in premium ranges like ABB S200. Types A and Z are used for protecting semiconductor circuits, measuring transformers, and electronics, while Type K is for motors with very high inrush currents. These are not used in typical residential distribution boards.

Breaking Capacity

This parameter indicates the maximum short-circuit current that the MCB can safely interrupt:

• 4.5 kA – the minimum level, acceptable for detached houses with a remote transformer.
• 6 kA – the most common value for the residential sector.
• 10 kA – for commercial buildings and premises located near a transformer substation.

The required value is determined by the calculated short-circuit current at the point of installation, rather than the type of building. According to EN/IEC 60898-1, the standard range includes 1500, 3000, 4500, 6000, and 10,000 A; for values exceeding 10,000 A, 20,000 A is the preferred value.

Number of Poles

• 1P (single-pole) – protects the phase conductor. Used in single-phase networks for individual lines.
• 2P (double-pole) – disconnects both the phase and the neutral simultaneously. Used as an incoming device in single-phase networks.
• 3P (triple-pole) – for three-phase loads (electric motors, three-phase cookers).
• 4P (four-pole) – an incoming device in a three-phase network, disconnecting all three phases and the neutral.

Coordination with RCDs and the Incoming MCB

There are two rules that are often overlooked. First: the rated current of an RCD installed downstream of an MCB must be equal to or greater than the rated current of that MCB (e.g., if the MCB is 25 A, the RCD should be 25 A or higher). Second is selectivity: branch MCBs should have a lower rating than the incoming MCB by at least one step. This ensures that in the event of a short circuit on a single line, only the branch device trips, rather than the main incoming device, which would de-energise the entire board.

Comparison of Popular Brands

Parameter	Generic Budget MCB	ABB S200	Schneider Electric iC60N	Legrand TX3
Breaking capacity (Icn)	4.5 kA	6 kA (S200M – 10 kA)	6 kA	6 kA at 400 V; 10 kA for 2P–4P at 230 V
Tripping characteristic	Not specified by manufacturer	Type C (Class 3)	Type C (Class 3)	Type C (Class 3) (for B and C up to 40 A)
Price segment	Budget	Premium	Premium	Mid-range

Selection Recommendations

• For apartments: 16 A Type C MCBs for socket circuits, 10 A for lighting, and a 32–40 A main switch.
• For residential houses: Type B or C characteristics, with a breaking capacity of at least 6 kA.
• For commercial premises: Selection based on specific technical requirements (e.g., 10 kA breaking capacity and required tripping characteristic); premium ranges from manufacturers such as ABB, Schneider Electric, Legrand, or Eaton are recommended.
• Budget options: Basic MCB series.