WNB1-63 MCB 6kA Miniature Circuit Breaker

An MCB is an electromechanical device that automatically protects an electrical circuit from damage caused by overload or short circuit. Housed in a compact DIN-rail module, it combines a thermal bimetal strip (slow trip on sustained overcurrent) and an electromagnetic solenoid (instant trip on high fault current). Unlike a fuse, it can be reset manually after the fault is cleared and is reusable indefinitely under normal service conditions.

On a mild overload, current heats a bimetallic strip that bends over seconds or minutes, releasing the mechanical latch to open the contacts. On a short circuit, the very high current energizes a solenoid that plunges an armature into the trip mechanism in 2–3 milliseconds, opening the contacts before damage occurs. An internal arc chute splits and cools the arc between opening contacts, extinguishing it safely.

6 kA is the rated ultimate short-circuit breaking capacity (Icn) — the maximum prospective fault current the MCB can interrupt at its rated voltage without failing. It is a measure of how strong the upstream supply can be while still expecting safe disconnection. Domestic installations typically see 3–6 kA fault levels, so a 6 kA MCB is adequate for most homes and small commercial panels.

Add up the load current on the circuit (e.g., total watts ÷ 230 V), multiply by 1.25 for margin, and choose the next standard MCB rating at or above that figure. Then verify that the downstream cable's current-carrying capacity (after derating for grouping, ambient temperature, and insulation) is at least equal to In. For example, a 2.5 mm² cable typically requires a 20 A or smaller breaker.

Choose Type B (3–5× In) for domestic lighting, heaters, and short cable runs where sensitive fault disconnection is needed. Choose Type C (5–10× In) for sockets, general commercial loads, and small motors. Choose Type D (10–20× In) only for loads with very high inrush, such as transformers, welders, and large direct-on-line motors. Never select D solely to stop nuisance tripping — it reduces protection sensitivity.

The WNB1-63 clips onto a standard 35 mm DIN rail. Connect the supply to the upper terminals marked "LINE" (or 1, 3, 5) and the load to the lower terminals marked "LOAD" (or 2, 4, 6). Strip conductors to the depth marked in the manual, insert fully under the screw clamps, and tighten to the specified torque. Polarity and phase sequence must match the marking on the device.

Common causes are overload (too many appliances on one circuit), a faulty appliance or cable with intermittent short circuit, loose terminals overheating the bimetal, or a wrong trip curve for the load. A short-circuit trip feels almost instantaneous, while an overload trip may take seconds to minutes. Unplug loads one at a time to isolate the faulty appliance, and inspect terminals for heat or discoloration.

IEC 60898-1 is the IEC product standard for AC miniature circuit breakers used in household and similar overcurrent protection. It defines rated voltages up to 440 V, rated currents up to 125 A, and breaking capacities from 1.5 kA upward, and specifies type tests for tripping characteristics, short-circuit performance, mechanical endurance, and temperature rise. A product marked "IEC 60898-1" has been third-party type-tested to these requirements.

No. An MCB only interrupts overcurrents and short-circuit currents; it cannot detect the small residual current (30 mA) that flows through a person to earth during an electric shock. For shock protection you need an RCD/RCBO, or an RCBO that combines both functions in one module. An MCB protects the installation and cables, not the person touching live parts.

They are widely used as branch-circuit protection in residential consumer units, commercial distribution boards, small industrial panels, HVAC control circuits, lighting and socket outlets, solar PV combiner boxes, and OEM equipment. The 6 kA rating is well suited to most low-voltage supplies where the upstream short-circuit level does not exceed 6 kA.