A CMC-MX series built-in bypass soft starter (380 V, 7.5–280 kW) is a modern motor starting and protection device that combines power electronics, a microprocessor and automatic control into one compact unit. The current transformer and bypass contactor are integrated inside the enclosure, so no external bypass components or separate current transformer are required — installation is simpler and panel space is saved.
Core Functions
1. Stepless smooth start and stop
The unit ramps the motor voltage continuously from standstill to full speed and ramps down on stop, with no step or jump in torque or current. Acceleration and deceleration are controlled smoothly rather than switched in stages.
2. Avoids mechanical and electrical shock of traditional starting
Direct-on-line (DOL), star-delta and autotransformer reduced-voltage starting all produce a sudden current inrush and a mechanical step when the starter switches state. A soft starter removes these shocks: there is no torque transient on engagement, no voltage dip on the supply network, and less stress on motor windings, couplings, belts, bearings and ductwork.
3. Reduces starting current and distribution capacity
By limiting and controlling starting current, the soft starter lowers the demand placed on the distribution network. This reduces the required installed capacity of the supply and avoids premature investment in capacity upgrades, while protecting the supply from large inrush peaks.
Why the Built-in Bypass Design Matters
Once the motor reaches full speed, the internal bypass contactor closes and carries the running current directly, bypassing the thyristors. The semiconductors only conduct during the ramp-up and ramp-down phases, which cuts continuous heat generation and conduction losses, removes the need for an external bypass contactor, and shortens the wiring list.
Field reference: for a real installation outcome, see the case study of a CMC-MX built-in bypass soft starter on process fans at a Zhejiang environmental plant — 350% Ie current limit, 15 s ramp and 40% initial voltage.
