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Innomotics 1PQ8 Compact Motors: 400kW vs 670kW — Choosing the Right VFD-Duty Motor for Heavy Industrial Loads

Some industrial processes don't run at a fixed speed. Cement kilns, large compressors, mining conveyors, and steel processing lines all need precise, variable speed control — and that means the motor driving them needs to be built specifically for converter (VFD) duty, not just a standard fixed-speed design pressed into a role it wasn't optimized for. That's exactly where Innomotics' 1PQ8 Compact Motor series comes in.

This guide compares two models from the 1PQ8 – N Compact Motors IE3 series — a 400kW, 1500 RPM unit and a 670kW, 750 RPM unit — and helps you understand which one fits your application.

What Makes the 1PQ8 Series a "Compact Motor" Built for VFD Duty?

The 1PQ8 – N series is engineered specifically for Converter (VFD) Duty Applications — meaning these motors are designed from the ground up to work with a variable frequency drive, delivering precise speed regulation and optimized torque across a range of operating speeds, rather than just running at a single fixed line speed.

Both motors in this comparison share the same core engineering foundation:

• IE3 Premium Efficiency technology — reducing electricity consumption without compromising performance
• 415V Delta (∆) configuration at 50Hz — standard industrial power supply compatibility
• Heavy-duty industrial construction — built for continuous, demanding operating conditions
• VFD compatibility — enabling precise speed control and improved process efficiency
• Low maintenance design — reducing unplanned downtime over the motor's service life

Where they differ is in power output, pole configuration, speed, and physical frame size — exactly the specifications that determine which motor fits which application.

Innomotics 1PQ8 356-4PB70 — 400kW, 1500 RPM, Frame 355

The Innomotics 1PQ8 356-4PB70 delivers 400kW output through a 4-pole configuration, running at 1500 RPM — a standard synchronous speed well-suited to applications that don't require heavily reduced output shaft speed. Built on Frame Size 355, this motor offers a strong balance of power and speed for a wide range of heavy industrial processes.

Typical applications: cement manufacturing, steel and metal industries, power generation facilities, oil & gas processing, chemical and petrochemical plants, industrial compressors and pumps, water treatment systems, and material handling equipment.

Best suited for: processes that operate efficiently at standard motor speeds (around 1500 RPM) without needing a large mechanical speed reduction between the motor and the driven equipment.

Innomotics 1PQ8 460-8PD00 — 670kW, 750 RPM, Frame 500

The Innomotics 1PQ8 460-8PD00 steps up substantially to 670kW output, but through an 8-pole configuration running at a much lower 750 RPM. Built on the larger Frame Size 500, this motor is purpose-built for applications needing stable low-speed performance with high torque output — exactly the profile needed for heavy, slow-turning industrial equipment where running the motor directly at a lower speed (rather than gearing down a faster motor) is the more efficient and mechanically simpler solution.

Typical applications: steel and metal processing plants, mining and material handling equipment, water treatment facilities, chemical and petrochemical plants, oil & gas processing units, and heavy industrial compressors and pumps.

Best suited for: heavy-duty equipment specifically requiring low-speed, high-torque operation — large mills, crushers, slow conveyors, and similar applications where a high-pole-count, low-RPM motor eliminates the need for extensive mechanical speed reduction.

Quick Comparison

Feature	1PQ8 356-4PB70	1PQ8 460-8PD00
Output Power	400 kW	670 kW
Pole Configuration	4 Pole	8 Pole
Speed	1500 RPM	750 RPM
Frame Size	355	500
Voltage	415V Delta (∆)	415V Delta (∆)
Efficiency Class	IE3	IE3
Duty Type	Converter (VFD) Duty	Converter (VFD) Duty
Best For	Standard-speed heavy industrial loads	Low-speed, high-torque heavy loads

How to Choose Between Them

• Does your driven equipment run efficiently at standard motor speed (around 1500 RPM) without heavy gear reduction? The 1PQ8 356-4PB70 at 400kW is the more directly suited option.
• Does your application demand low-speed, high-torque operation — large mills, crushers, or heavy slow-turning equipment? The 1PQ8 460-8PD00 at 670kW and 750 RPM is built specifically for that profile.
• Either way, confirm your actual load torque and speed requirements against the motor's rated output — pole count and speed matter just as much as raw kW output when matching a motor to mechanical equipment.
• Check your VFD's compatibility and sizing against the selected motor's power and voltage requirements, since both motors are designed specifically for converter duty rather than direct-on-line operation.

Why Converter (VFD) Duty Motors Matter for These Applications

A motor not specifically rated for VFD duty can suffer from issues like reduced cooling at low speeds (since built-in cooling fans often depend on shaft rotation speed) or insulation stress from the switching characteristics of variable frequency drives. The 1PQ8 series is engineered around these considerations from the start, which matters significantly for continuous, heavy-duty industrial processes where motor reliability directly affects plant uptime.

For a broader look at Innomotics motor technologies — including cast iron construction and severe duty options — see our Innomotics Severe Duty Motors guide and Why Cast Iron Motors Are Built for Tough Industrial Applications.

Why Buy Genuine Innomotics 1PQ8 Compact Motors from SB Smart

At this power range, a motor represents a substantial capital investment — getting the pole configuration, speed, and frame size right at the specification stage matters enormously. SB Smart (sbsmart.in), the official e-commerce portal of S.B. Syscon Pvt. Ltd., supplies genuine Innomotics 1PQ8 Compact Motors along with the broader Innomotics motor range, backed by GST invoicing, expert technical guidance, and PAN India delivery.

Frequently Asked Questions (FAQ)

1. What is the difference between the 1PQ8 356-4PB70 and 1PQ8 460-8PD00? The 1PQ8 356-4PB70 delivers 400kW at 1500 RPM through a 4-pole design, while the 1PQ8 460-8PD00 delivers 670kW at 750 RPM through an 8-pole design, making it better suited for low-speed, high-torque applications.

2. What does "Converter (VFD) Duty" mean? It means the motor is specifically engineered to operate with a variable frequency drive, enabling precise speed regulation and optimized torque delivery across a range of speeds, rather than being limited to fixed-speed, direct-on-line operation.

3. Why would I choose a lower RPM motor like the 460-8PD00 over a higher RPM one? Lower RPM, higher-pole-count motors are chosen when the driven equipment needs low-speed, high-torque operation directly, avoiding the need for extensive mechanical gear reduction between motor and equipment.

4. What efficiency class do these motors use? Both the 1PQ8 356-4PB70 and 1PQ8 460-8PD00 are built to IE3 Premium Efficiency standards.

5. What voltage configuration do these motors run on? Both motors operate on 415V Delta (∆) configuration at 50Hz.

6. Which industries typically use these compact motors? They are used in cement manufacturing, steel and metal processing, mining, water treatment, chemical and petrochemical plants, oil and gas processing, and heavy industrial compressors and pumps.

7. How do I know which frame size fits my application? Frame size should be confirmed against your existing mounting and coupling arrangement — the 1PQ8 356-4PB70 uses Frame 355, while the larger 1PQ8 460-8PD00 uses Frame 500.

8. Where can I buy genuine Innomotics 1PQ8 Compact Motors in India? SB Smart (sbsmart.in) supplies genuine Innomotics 1PQ8 Compact Motors with GST invoicing, technical support, and PAN India delivery.

Final Thought

Choosing between the 400kW 1PQ8 356-4PB70 and the 670kW 1PQ8 460-8PD00 isn't simply a matter of picking the higher power rating — it's about matching pole count, speed, and torque characteristics to exactly what your driven equipment needs. Whether your process runs efficiently at standard motor speed or demands the low-speed, high-torque profile of the 8-pole design, both motors bring the same IE3 efficiency and VFD-duty engineering to heavy industrial applications where reliability and precise speed control genuinely matter.