WNB1-63 3P MCB 6kA Three Pole Circuit Breaker

A three-pole MCB is a DIN-rail breaker that switches and protects the three phase conductors (L1, L2, L3) of a three-phase circuit on a single handle. It is used to protect three-phase loads such as motors, heaters, three-phase sockets, and branch feeders in commercial and industrial distribution boards.

The 6 kA rating means the breaker can safely interrupt a prospective short-circuit current of up to 6000 A. In a three-phase system a bolted fault can reach very high currents near the transformer, so the 6 kA rating must be at least the calculated fault level at the breaker's position; otherwise the breaker may be destroyed on a major fault.

Inside, a thermal bimetallic strip provides delayed overload protection, and an electromagnetic solenoid provides instantaneous short-circuit tripping. All three poles are mechanically coupled so that an overload or short on any phase opens all three phases simultaneously, with the arc contained and cooled in internal arc chutes.

For direct motor starting with high locked-rotor current, a Type C or D curve is normally used to tolerate the starting inrush without nuisance tripping. Type D trips at a higher multiple (roughly 10–20× In) for the heaviest inrush, while Type C (roughly 5–10× In) suits lighter motor and general three-phase loads — match the curve to the actual starting current.

A 3P MCB does not switch or protect the neutral; the neutral is connected directly to the neutral busbar, and the protective earth goes to the earth bar. Only the three phases pass through the breaker, which is why this device is used when the neutral should remain continuous and unswitched.

Work out the three-phase load's full-load current, size the phase conductors to carry it, and choose an In above the design current but within the cable ampacity. Add derating for ambient temperature and grouping, and select the B/C/D curve according to the load's inrush characteristics.

Snap the WNB1-63 onto a standard 35 mm DIN rail in the board, connect the three incoming phases to the line terminals and the outgoing phases to the load terminals (observing the marked direction), and tighten each terminal to the datasheet torque. Leave the supply isolated until wiring is complete and polarity/phase labels are checked.

Available short-circuit current rises sharply close to a large transformer and short, low-impedance cables. A 6 kA breaker must not be used where the calculated fault current exceeds 6 kA, or it may fail to clear — for very high-fault locations you need a higher kA rating or upstream discrimination/coordination.

If the breaker trips, first determine whether it was an overload (thermal trip, delayed) or a short circuit (instantaneous trip). Remove loads to test for overloading, inspect for a faulted three-phase appliance or damaged cables, and check loose or overheated terminals. Do not reclose repeatedly if a fault remains.

As a low-voltage MCB, the WNB1-63 3P unit is designed to IEC 60898-1 and typically carries CE marking. Refer to the product datasheet for its exact rated current, breaking capacity (6 kA), and trip-curve options to confirm they match the intended three-phase application.