For three-phase industrial motors, the industry-recognized rule of thumb is that when the motor power rating is equal to or above 22KW, it is highly recommended—and in many facilities, mandatory—to use a Star-Delta (Wye-Delta) starting electric box.

Here is a detailed breakdown of why this threshold exists, the specific situations it applies to, and how XINYI MACHINERY implements this standard.

Why the 22KW Threshold?

Above 22KW, Direct-On-Line (DOL) starting generates an inrush current that is 6 to 7 times the motor's full-load current. This massive surge can cause significant voltage drops across the power grid, tripping circuit breakers, damaging contactors, and interfering with other sensitive equipment on the same line. The Star-Delta starter reduces this starting current to approximately 1/3 of the DOL current (about 2 to 2.5 times the full-load current), ensuring a much safer, smoother ramp-up while protecting both the motor windings and the electrical infrastructure.

Specific Situations for Plastic Recycling Equipment

For your equipment lines, the Star-Delta starting box is specifically suggested in the following scenarios:

1. High-Inertia Plastic Crushers – When processing thick-walled purgings, lump materials, or hard engineering plastics, the rotor and flywheel create massive inertia. Star-Delta ensures these heavy rotors accelerate gradually without overheating the stator.

2. Heavy-Duty Single-Shaft & Dual-Shaft Shredders – Shredders often start under heavy load (especially when "spike" or "head" materials get lodged). In these cases, we pair the Star-Delta box with a PLC-controlled auto-reverse function. If the motor stalls due to jamming, the system instantly switches the sequence to reverse the motor, clears the blockage, and reverts to forward rotation—all handled safely under the reduced-current Star-Delta logic.

3. Plastic Granulators / Agglomerators – The main extruder screw motors frequently exceed 22KW. Using Star-Delta starting protects the expensive gearbox from sudden torque shocks and prevents the screw from seizing during cold starts.

⚠️ Critical Prerequisites

While we suggest Star-Delta for ≥22KW, please ensure these conditions are met before applying it:

· Motor Wiring: The motor must have 6 terminals (both ends of each winding accessible) and be rated for Delta (Δ) operation at the supply voltage.

· Torque Limitation: Starting torque is also reduced to ~33%. Therefore, do not use Star-Delta if your machine requires 100% full-load torque right at the moment of start-up (e.g., if the shredder chamber is completely filled with solid metal).

· Duty Cycle: This starter is designed for infrequent starting (e.g., 5-10 starts per hour). If your automation requires constant on/off cycling, a soft starter or VFD is the better alternative.

About XINYI MACHINERY – Your Comprehensive Partner

As a leading Chinese manufacturer with decades of experience in the plastics recycling industry, XINYI MACHINERY integrates this electrical standard into all our heavy-duty machinery.

We pride ourselves on being a one-stop solution provider, manufacturing a full spectrum of equipment, including:

· Plastic Crushers & Granulators (from small beside-the-press units to large 150HP central granulators).

· Heavy-Duty Plastic Shredders (single-shaft, double-shaft, and four-shaft configurations).

· Plastic Granulator Machines & Agglomerators for reprocessing film, fibers, and rigid plastics.

· Plastic Recycling Machines (complete washing and pelletizing lines).

· Blade Grinding Machines to keep your cutting tools sharp and efficient.

· Industrial Balers for compressing waste film, bottles, and rigid plastics.

· High-Speed Plastic Mixers for color masterbatch and compounding.

For all our machinery equipped with main motors ≥ 22KW, we factory-configure the Star-Delta starting electric box as a standard feature. This ensures our global clients receive equipment that not only delivers high throughput but also complies with international electrical safety standards, particularly in regions with unstable voltage grids.

If your specific application requires a custom solution (e.g., explosion-proof boxes or integration with VFDs for energy saving), our engineering team is ready to tailor the electrical panel to your precise workshop conditions.