How to choose a miniature circuit breaker: tripping curve B/C/D, rated current, breaking capacity (kA), number of poles, and how to size an MCB for a lighting or motor circuit to IEC 60898.
A miniature circuit breaker (MCB) is the default overcurrent protector in every low-voltage distribution board: it carries the load continuously and trips automatically on overload or short circuit, then resets by hand instead of being discarded like a fuse. For panel builders, distributors and importers, the catalogue number is fixed by four choices — curve, rated current, breaking capacity and pole count — and getting them wrong means either nuisance trips or a board that cannot survive a fault. This guide walks the choices.
The letter is the magnetic trip threshold in multiples of rated current (In):
| Curve | Magnetic trip | Use |
|---|---|---|
| B | 3–5 × In | Resistive loads, lighting, low inrush — homes and offices |
| C | 5–10 × In | General mix of lighting + sockets; the common commercial default |
| D | 10–20 × In | Transformers, motors, capacitive loads with high inrush |
Curve C suits most panels; pick D for anything with a hard start (motor, welding transformer, large LED driver) and B only where inrush is genuinely tiny. A D-curve on a plain lighting circuit will not nuisance-trip but also masks a fault longer than it should.
In is the current the MCB carries forever without tripping. Size it from the circuit load with headroom, not to the cable's limit:
This is the fault current the MCB can safely interrupt once. A 6 kA device is fine for a final sub-circuit fed from a limiting upstream breaker, but the main incomer or a board close to a transformer may see tens of kA, where you need 10 kA or higher. Match the kA rating to the prospective short-circuit current at that point in the board, confirmed by the upstream protective device.
In TN-C-S and TT systems the neutral-handling rule varies; size poles to the circuit topology and local wiring code, not habit.
Domestic and similar boards use IEC 60898 (rated up to 125 A, 440 V); industrial assemblies reference IEC 60947-2. Confirm the MCB matches the busbar and DIN rail of the board you are building, the trip characteristics your code expects, and any required markings (CE, ROHS). Mixing a 60898 device into a 60947-2 assembly changes the standards basis of the whole board.
ELEHPD manufactures DIN-rail MCBs in curves B, C and D, from 1 A to 63 A, in 6 kA and 10 kA breaking capacities, 1P–4P, built to IEC 60898 and made to drop straight onto standard 35 mm rails alongside RCCBs, contactors and din-rail power supplies.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.