Westhomes Factory Wsb9sz-125 Air AC Electrical Miniature Circuit Breaker 6-100A MCB 3p

A 3-pole MCB opens all three phase conductors (L1, L2, L3) simultaneously. This guarantees that no phase remains live through a fault and that three-phase motors or three-pole loads are fully disconnected. It is the standard protective device for 400 V three-phase distribution, motor circuits, and three-phase sub-boards.

"Air" indicates that arc extinction takes place in air rather than in oil, vacuum, or SF6. When the contacts open, the resulting arc is forced into a stack of metal grids (an arc chute) that splits, cools, and extinguishes it using the surrounding air as the insulating medium. This is the standard technology for miniature and moulded-case breakers up to 1000 V.

Motor circuits normally use Curve D, which trips magnetically at 10–20 × In and tolerates the 5–7 × inrush of direct-on-line starting without nuisance tripping. Curve C is fine for static three-phase loads such as rectifiers, heaters, and distribution boards, while Curve B is reserved for low-inrush resistive circuits.

Compute the full-load current Ib from the rated power, voltage, and power factor, then pick the next standard rating such that Ib ≤ In ≤ Iz. For motor loads, also add allowance for starting: set In around 1.1–1.25 × Ib, and rely on a D-curve to absorb starting inrush rather than over-sizing the breaker.

Yes. The breaker is marked with line (mains supply) on one end and load (downstream circuit) on the other. Reverse wiring can degrade arc extinction because the arc chute geometry and magnetic blow-out are designed for current flowing in the declared direction. Always wire supply in on the top terminals and load out on the bottom, unless the datasheet explicitly permits back-fed wiring.

Overload protection is provided by the thermal bimetal, which trips in seconds to minutes depending on how far the current exceeds In, protecting cables from overheating. Short-circuit protection is provided by the magnetic solenoid, which trips in milliseconds when the fault current exceeds the curve threshold, clearing the fault before cables or equipment suffer thermal damage.

The WSB9SZ-125 3P is rated to a declared short-circuit breaking capacity (commonly 6 kA or 10 kA) shown on the nameplate as Icn/Icu. Before installation, calculate the prospective short-circuit current at the panel based on transformer kVA, upstream impedance, and cable length; if it exceeds the breaker rating, upstream coordination or a higher-rated breaker is required.

Yes, the 3-pole body is designed for standard 35 mm DIN rail mounting in industrial or consumer distribution boxes. Snap the top hook over the rail and press the bottom until it latches. Allow adequate wiring bend radius above and below, and group it with upstream and downstream breakers so selectivity (discrimination) can be achieved.

Instantaneous (magnetic) trips on energisation point to a bolted short circuit downstream rather than an overload. Isolate the load, inspect the wiring for damaged insulation or a bridged terminal, and megger the circuit before re-energising. If no fault is found on the wiring, suspect a failed device on the load side or an incorrectly selected curve that is too sensitive for a high-inrush motor.

As a low-voltage AC miniature circuit breaker in the 6–100A range, it is built to IEC 60898-1 and affixed with the CE mark. The nameplate carries the rated voltage (Ue), rated current (In), tripping curve, short-circuit breaking capacity, and the relevant standard number; retain the datasheet for compliance records in commercial and industrial installations.