MCC Panels

Soft Starters in Motor Control Center (MCC)

Soft Starters selection, integration, and best practices for Motor Control Center (MCC) assemblies compliant with IEC 61439.

Soft Starters in Motor Control Center (MCC)

Overview

Soft starters in Motor Control Center (MCC) assemblies are used to limit inrush current, reduce mechanical stress on the driven load, and improve process continuity during motor starting. In IEC 61439-2 low-voltage switchgear and controlgear assemblies, the soft starter must be selected not only for motor duty, but also for its contribution to assembly temperature rise, short-circuit coordination, and functional segregation within the MCC lineup. Typical applications include pumps, fans, compressors, conveyors, crushers, mixers, and HVAC systems where controlled acceleration and deceleration are preferred over direct-on-line starting. In an MCC, a soft starter is commonly paired with a line isolator or MCCB, semiconductor or thermal overload protection as applicable, and a bypass contactor for reduced losses during run mode. The upstream protective device may be an MCCB, fuse switch disconnector, or ACB, sized in accordance with IEC 60947-2 and IEC 60947-4-1 coordination requirements. Downstream motor protection should consider motor full-load current, starting duty, acceleration time, number of starts per hour, and the load torque curve. For larger motors, selection may extend to 200 A, 320 A, 630 A, or higher current classes, while the MCC busbar system must be verified for the total diversity of all feeders and the prospective short-circuit current, often 25 kA, 36 kA, 50 kA, 65 kA, or higher depending on site fault level. Thermal management is critical because soft starters dissipate heat during ramp-up and, if bypass is not used, during continuous operation. The assembly must be evaluated for internal temperature rise, ventilation strategy, derating due to altitude or ambient temperature, and the heat contribution of neighboring devices such as VFDs, protection relays, and PLC I/O modules. IEC 61439-1 and IEC 61439-2 require verification of temperature-rise limits, dielectric properties, clearances, creepage distances, and short-circuit withstand. For industrial MCCs, form of separation often ranges from Form 2b to Form 4b, depending on required maintainability and fault containment between functional units. Soft starters integrated in intelligent MCC panels are frequently equipped with Modbus RTU, Modbus TCP, Profibus, Profinet, EtherNet/IP, or Ethernet-based gateway modules for SCADA and BMS monitoring. Common data points include start/stop status, current, voltage, power, fault history, phase loss, overload, thyristor bypass status, and number of starts. In process facilities, this enables predictive maintenance and better coordination with upstream relays and downstream motor loads. Where the MCC is installed in hazardous areas or adjacent to classified zones, equipment selection should also consider IEC 60079 requirements for explosion-protection interfaces, and where arc-flash mitigation is a concern, assembly design may be validated against IEC 61641 for internal arc effects. Practical configuration in an MCC typically includes draw-out or fixed feeders, branch circuit grouping by process area, a terminal compartment for field wiring, and clearly defined separation between control, power, and communication circuits. For motors with high inertia loads, the soft starter must support adjustable current limit, kick-start, ramp profiles, and soft stop. For fans and pumps, reducing hydraulic shock and belt stress is a key benefit. In engineered MCC panels from Patrion, soft starters are integrated with IEC 61439-2 verified busbar systems, coordinated protection devices, and thermally managed enclosures to deliver reliable motor control in compact, maintainable, and standards-compliant assemblies.

Key Features

  • Soft Starters rated for Motor Control Center (MCC) operating conditions
  • IEC 61439 compliant integration and coordination
  • Thermal management within panel enclosure limits
  • Communication-ready for SCADA/BMS integration
  • Coordination with upstream and downstream protection devices

Specifications

PropertyValue
Panel TypeMotor Control Center (MCC)
ComponentSoft Starters
StandardIEC 61439-2
IntegrationType-tested coordination

Other Components for Motor Control Center (MCC)

Moulded Case Circuit Breakers (MCCB)

Branch protection 16A–1600A, thermal-magnetic or electronic trip

Variable Frequency Drives (VFD)

Motor speed control, energy savings, 0.37kW–500kW+

Contactors & Motor Starters

DOL/star-delta/reversing starters, overload relays, Type 2 coordination

Protection Relays

Overcurrent, earth fault, differential, generator protection relays

Busbar Systems

Copper/aluminum busbars, busbar supports, tap-off units

PLCs & I/O Modules

Programmable logic controllers, remote I/O, fieldbus communication

Other Panels Using Soft Starters

Custom Engineered Panel

Bespoke panel assemblies for non-standard requirements — special ratings, unusual form factors, multi-function combinations.

Soft Starter Panel

Enclosed soft starter assemblies for reduced voltage motor starting with torque control, ramp-up/down profiles, and bypass contactor options.

Frequently Asked Questions

Selection starts with motor full-load current, starting torque requirement, starts per hour, and load inertia, then checks assembly constraints under IEC 61439-1 and IEC 61439-2. The soft starter’s current rating must match the motor duty and ambient derating, while the MCC busbar and feeder protection must withstand the prospective short-circuit current. In practice, the feeder often uses an MCCB or fuse protection coordinated to IEC 60947-2, with the soft starter sized for the application category and bypass arrangement. You also need to verify enclosure ventilation, cable compartment space, and temperature-rise contribution from adjacent devices.
A bypass contactor is strongly recommended in most MCC applications because it removes semiconductor losses after motor acceleration, reducing heat inside the enclosure and improving efficiency. This is especially important in compact MCC sections with multiple feeders, VFDs, and relays. Under IEC 61439 verification, the thermal profile of the complete assembly must be assessed, so bypassing can materially improve compliance margins. In continuous-duty or high-cycle applications, bypass also extends the life of the soft starter. Some compact soft starter designs integrate an internal bypass, while larger industrial feeders use an external IEC 60947-4-1 contactor.
The feeder short-circuit rating must be coordinated with the MCC’s declared assembly short-circuit withstand current, which is verified under IEC 61439-1/2. Typical industrial values may be 25 kA, 36 kA, 50 kA, 65 kA, or more, depending on the site fault level and upstream transformer capacity. The soft starter itself is not usually the sole protective device, so its SCCR or conditional short-circuit current rating must be checked together with the upstream MCCB, fuses, or ACB. Correct coordination ensures the feeder survives a fault without damaging busbars, terminals, or adjacent functional units.
Yes. Most modern soft starters support communications such as Modbus RTU, Modbus TCP, Profibus, Profinet, or EtherNet/IP, allowing integration into SCADA and BMS systems. In MCC panels, this is used for remote start/stop, status feedback, fault logs, current monitoring, and maintenance diagnostics. The communication architecture should be segregated from power wiring and designed to the panel’s wiring practices under IEC 61439. For larger facilities, integration with protection relays, PLCs, and energy meters gives a complete operational picture and supports predictive maintenance.
Soft starters generate heat during motor ramp-up and, if no bypass is used, during steady-state operation. The MCC designer must check internal temperature rise per IEC 61439-1 and ensure that adjacent devices do not exceed their allowable thermal limits. Key variables include enclosure size, ambient temperature, ventilation, mounting spacing, cable duct loading, and simultaneous load diversity. If the MCC includes ACBs, MCCBs, VFDs, and protection relays in the same lineup, thermal stacking can become significant. Derating may be required for altitude, high ambient conditions, or sealed IP-rated enclosures.
The MCC assembly is primarily governed by IEC 61439-1 and IEC 61439-2, while the soft starter and associated switching/protection devices fall under IEC 60947-4-2 and related parts of IEC 60947. If the installation is in a hazardous area, IEC 60079 must be considered for explosion protection interfaces. Where arc containment or operator protection is a design objective, IEC 61641 is relevant for internal arc effects. For an engineered MCC, compliance is achieved by verifying the entire assembly, not just the component nameplate ratings.
Soft starter feeders are commonly arranged in Form 2b, Form 3b, or Form 4b depending on the required level of segregation and maintainability. Form 2b typically separates busbars from functional units, while Form 3 and Form 4 introduce additional separation for terminals and adjacent feeders. In MCCs with frequent maintenance or critical process uptime, higher forms of separation are preferred because they help isolate faults and allow safer servicing. The chosen form must be consistent with the assembly design, cabling layout, and verified IEC 61439 construction approach.
Use a soft starter when the primary need is reduced inrush current, smoother acceleration, and lower mechanical stress, but not full speed control during operation. This suits pumps, fans, conveyors, and compressors where the motor normally runs at line frequency. A VFD is better when speed regulation, torque control across the full operating range, or energy savings from variable flow are required. In MCC design, soft starters are usually simpler, cooler, and less demanding on harmonics than VFDs, which can be advantageous in compact IEC 61439 assemblies with limited thermal headroom.

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