How do I select a soft starter for a custom engineered panel under IEC 61439?

Start with motor full-load current, starting frequency, load inertia, and required ramp time. Then verify the soft starter’s rated operational current, ambient derating, and duty class against the actual enclosure conditions. Under IEC 61439-2, the assembly designer must also confirm temperature-rise performance, busbar loading, protective device coordination, and short-circuit withstand. In practice, the soft starter must be matched with an MCCB, fuse, or ACB upstream according to the manufacturer’s coordination data. For PLC-integrated panels, choose models with Modbus, PROFINET, or EtherNet/IP if status and diagnostics are needed in SCADA or BMS.

What short-circuit protection is required for soft starters in industrial panels?

Soft starters usually require upstream short-circuit protective devices such as gG fuses, a motor-protective MCCB, or an ACB feeder, depending on the manufacturer’s Type 1 or Type 2 coordination data. The target is to ensure the soft starter survives or is safely isolated during a fault while maintaining the panel’s declared short-circuit rating. IEC 60947-4-2 governs motor controllers and soft starters, while IEC 61439 requires the assembly builder to verify the complete feeder arrangement. Always use the manufacturer’s coordination tables for the exact device combination, prospective fault current, and installed line voltage.

Can soft starters be used instead of VFDs in custom engineered panels?

Yes, when the application only needs reduced-voltage starting and stopping, not variable speed control. Soft starters are commonly used on pumps, fans, compressors, and conveyors where the objective is to reduce mechanical shock and inrush current. If the process requires speed regulation, torque control over a wide range, or energy optimization through variable flow, a VFD is typically the better choice. In custom engineered panels, the choice should be based on process requirements, harmonic constraints, heat dissipation, and cost. Soft starters also tend to generate less EMI and have simpler installation than VFDs.

How much heat do soft starters add to a panel enclosure?

Soft starters add measurable thermal losses because their thyristors dissipate power during ramping and, in some models, during bypass transition. The heat load depends on motor current, start duration, and whether the device uses an internal or external bypass contactor. In IEC 61439-2 assemblies, this heat contribution must be included in the enclosure temperature-rise assessment. For high-duty applications or multiple starters in one section, panel builders often need ventilation, air conditioning, or compartmentalization. Manufacturer data sheets usually provide power dissipation in watts at rated current, which should be used in the thermal calculation.

What is the difference between direct-on-line and inside-delta soft starter wiring?

Direct-on-line wiring places the soft starter in series with the motor feeder and is simpler to design, wire, and commission. Inside-delta wiring connects the starter to the motor winding delta circuit and reduces the current through the soft starter by roughly 58%, which can allow a smaller device for the same motor. However, inside-delta configuration is more complex and requires a motor with six accessible terminals, correct wiring, and careful coordination of protection. In custom engineered panels, this option is often chosen for larger motors where enclosure space or device cost is a concern.

Do soft starters support SCADA or BMS integration in panel assemblies?

Yes, many modern soft starters support industrial communication for diagnostics and remote control. Common protocols include Modbus RTU, Modbus TCP, PROFINET, EtherNet/IP, and in some HVAC-oriented designs, BACnet integration via gateway. Typical data points include start/stop status, current, fault codes, bypass status, thermal utilization, and event history. In an IEC 61439 custom engineered panel, the comms interface should be planned alongside the control voltage, PLC I/O, and network architecture so that wiring segregation, EMC practices, and maintenance access are preserved.

What enclosure and cooling considerations apply to soft starters in panels?

Soft starters should be installed with enough clearance for airflow, cable bending radius, and maintenance access. Because semiconductor losses raise internal temperature, the enclosure may need natural convection, forced ventilation, a panel cooler, or segregation into a dedicated motor control section. Under IEC 61439-1/2, the assembly designer must verify temperature rise, especially when multiple power electronics devices are grouped together. Cooling selection depends on ambient temperature, IP rating, pollution level, and continuous load profile. If the panel is in a hot plant room or outdoor kiosk, derating is often necessary.

Which IEC standards apply to soft starters in custom engineered panels?

The core standards are IEC 61439-1 and IEC 61439-2 for low-voltage switchgear and controlgear assemblies, and IEC 60947-4-2 for semiconductor motor controllers and soft starters. Device coordination and protective behavior also rely on IEC 60947 principles. If the panel is located in a hazardous area, IEC 60079 requirements may apply to the surrounding installation. Where internal arc classification is specified, IEC 61641 becomes relevant for the panel enclosure. In practice, the panel builder must verify thermal performance, short-circuit withstand, clearances, creepage, and protective bonding for the complete assembly.

Panel + Component

Soft Starters in Custom Engineered Panel

Soft Starters selection, integration, and best practices for Custom Engineered Panel assemblies compliant with IEC 61439.

Overview

Soft starters in custom engineered panel assemblies are used to limit inrush current, reduce mechanical stress on driven equipment, and provide controlled acceleration and deceleration for induction motors in pumps, fans, compressors, conveyors, crushers, and HVAC plant. In IEC 61439-2 custom engineered panels, the soft starter must be selected as part of the assembly verification process, not as a standalone device. That means its rated operational current, heat dissipation, control supply, bypass arrangement, and short-circuit protection must be coordinated with the panel busbars, feeder devices, enclosure ventilation, and the declared assembly rating. Typical devices include motor soft starters with integrated semiconductor firing control, built-in overload protection, internal bypass contactors, and communication options such as Modbus RTU, Modbus TCP, PROFINET, EtherNet/IP, or BACnet gateway integration. Common product families used in industrial panel design include ABB PSTX, Schneider Electric Altistart, Siemens 3RW, and Danfoss soft starter ranges. For demanding duty cycles, external line contactors, semiconductor coordination fuses, or molded case circuit breakers (MCCBs) are often required to achieve the required SCCR and Type 2 coordination. In larger feeder sections, the soft starter is typically installed downstream of an ACB or MCCB incomer, with separate control power protection and an upstream short-circuit protective device sized per the manufacturer’s coordination tables. Selection for a custom engineered panel should start with motor FLA, starting duty, load inertia, starts per hour, and ambient temperature inside the enclosure. A soft starter rated at 100 A may not be suitable at 40 °C if derating applies, especially when multiple feeders are grouped in one section. Thermal management is critical because thyristor losses can materially increase internal temperature rise; panel builders often need forced ventilation, heat exchangers, or segregated cubicles to stay within IEC 61439 temperature-rise limits. When harmonic performance and energy savings are priorities, a soft starter may be preferred over a VFD if speed control is not required; however, a VFD is still the better option for variable torque or closed-loop process control. From a panel architecture perspective, the soft starter can be integrated in direct-on-line, inline, or inside-delta configurations, depending on current reduction targets and equipment topology. Inside-delta arrangements reduce device current but require careful wiring and coordination. For critical plant, soft starters are frequently paired with bypass contactors to minimize heat after ramp-up and improve efficiency. The complete feeder must also satisfy IEC 60947 device coordination rules, and the assembly must be checked for short-circuit withstand, dielectric performance, and protective bonding. In hazardous areas, adjacent equipment interfaces may also need consideration of IEC 60079 requirements, while arc fault containment or internal arc robustness may be relevant where IEC 61641 panels are specified. For facility managers and EPC contractors, the practical value is reduced motor stress, improved process reliability, and easier integration into SCADA or BMS systems for alarms, trips, motor current, and bypass status. In custom engineered panels, the soft starter is therefore not just a motor control device; it is a coordinated component whose electrical ratings, heat load, protection strategy, and communications must align with the overall IEC 61439 assembly design and the real operating profile of the installation.

Key Features

Soft Starters rated for Custom Engineered Panel 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

Panel Type	Custom Engineered Panel
Component	Soft Starters
Standard	IEC 61439-2
Integration	Type-tested coordination

Back to Hubs

Custom Engineered Panel

Soft Starters

Frequently Asked Questions

Need a Custom Panel Built to Spec?

Patrion's engineering team designs and manufactures IEC 61439 compliant panels. Get a design review or quote.

Contact Patrion Call +90 232 332 22 78