Motor Fundamentals & Efficiency2 / 13
Efficiency Classes & Losses
IE1/IE2/IE3/IE4 standards, where energy is lost (friction, heat, slip), and payback for upgrades.
10 min read · Jacob Willis, Net Zero Lead · Last reviewed July 2026
Motor efficiency is standardised into internationally agreed bands, the IE classes, and UK law now sets a floor under them: most new three-phase motors must be at least IE3, and the mid-range sizes IE4. For an energy manager the classes turn efficiency from a brochure claim into a comparable, regulated number, and the interesting question becomes economic: when is a class above the legal floor worth paying for? The arithmetic in this lesson answers it.
In this lesson
- 01The classes and the law
- 02What a class step is worth
- 03Policy, not purchase-by-purchase heroics
- 04Sources and further reading