VFD Energy Efficiency: IES Classes & How Drives Save Power

VFD system efficiency is now rated under IEC 61800-9-1 with IES classes (IES0, IES1, IES2), which cover the complete drive-motor system – and the real savings come from the application, not the drive alone. On pumps and fans, a VFD typically cuts absorbed power by 20–50% because load power follows the cube of speed, while throttling wastes the same energy. This article explains IES classes, where savings really come from, the hidden losses (harmonics, standby power) that reduce them, and how to get the best system efficiency.

What IES Class Means (IEC 61800-9-1)

IEC 61800-9-1 introduced the IES (International Energy efficiency class for Systems) rating, replacing the older approach of rating only the drive. It evaluates the whole speed-regulated system – motor plus drive – as one unit, with classes IES0 (lowest) up to IES2 and beyond. A higher IES class means lower system losses for the same output. Related parts of the IEC 61800 family cover general requirements (IEC 61800-4) and safety (IEC 61800-5), so a specification that asks for "IES2" is asking for a measurable, standardised efficiency level rather than a marketing claim.

Where VFD Savings Really Come From

For centrifugal pumps and fans, absorbed power is roughly proportional to the cube of speed: running at 80% speed uses about 51% of full-speed power. Compared with throttling a fixed-speed machine – where the motor keeps drawing nearly full power – a VFD converts that difference into real savings. Typical results: 20–50% reduction in absorbed power for pumps and fans with variable demand; constant-torque loads (conveyors, mixers) save less energy but still gain soft start and process control. See our energy savings guide for the calculation method.

Hidden Losses That Eat Into Savings

• Harmonics: drive-generated harmonics add losses to transformers, cables and motors; line reactors or multi-pulse/active-front-end drives reduce them
• Standby power: a typical drive draws tens of watts in standby – 20–50 W on mid-size units – which matters for 24/7 installations
• Carrier frequency: higher switching frequency reduces motor noise but increases drive losses; match it to the application
• Oversizing: a drive sized far above the motor runs inefficiently at low load; size for the actual duty
• Poor voltage quality: input unbalance and low voltage increase motor losses and drive stress

Real-World Savings Ranges

How to Maximize System Efficiency

• Size correctly: match the drive to the motor's actual full-load current, not an inflated margin – see our sizing guide
• Control by the process: close the loop (DO, level, pressure, temperature) so the drive only produces the energy actually needed
• Manage harmonics: add line reactors where the supply is weak; consider active front ends on large plants
• Use energy-optimising modes: many drives offer efficiency-optimising control that reduces magnetising current at light load
• Choose an IES2-rated system for new installations where the extra efficiency pays back over years of operation

Frequently Asked Questions

Does a VFD itself waste more energy than it saves? No. A drive's own losses are a few percent of rated power; on variable-demand pumps and fans, the cube-law saving is many times larger. The drive losses matter mainly in low-load, 24/7 cases.

What does "IES2" mean on a VFD datasheet? It is the IEC 61800-9-1 system efficiency class – the higher the class, the lower the motor+drive system losses. See our VFD FAQs for more on ratings and where efficiency matters most.

Want a realistic savings estimate for your plant? Our engineers can size, model and quantify the payback. Explore the medium-voltage VFD range for larger drives.