How electric motors are made in India
An induction motor starts as coils of electrical steel. Laminations are punched for the stator and rotor, stacked and pressed. The stator slots are lined with insulation paper, wound with enamelled copper wire by machine or by hand, and the winding is varnish-impregnated and baked. The rotor stack is usually die-cast with aluminium bars and end rings to form the squirrel cage, then pressed onto a machined shaft and balanced. The frame, end shields and terminal box are cast or fabricated and machined; bearings, fan and cowl are fitted, and the motor goes to the test bench before painting and packing.
The steel grade, the amount of copper and the quality of the rotor casting decide the losses, and so the efficiency class. A motor can look identical and run normally on a no-load test while being a lower efficiency class than the nameplate says.
The Coimbatore district administration states that the first motor made in India came from a small engineering shop in Coimbatore, Tamil Nadu, and that the city's motor and pump industry supplies over 40% of India's requirements. Motors are also made in many other states. India exported US$902.1 million under HS 8501 in FY2025-26 according to Department of Commerce TradeStat; the figure is provisional and the heading includes generators.
What we check on electric motors
| Check | How it is checked | What fails |
|---|---|---|
| Winding resistance | Measured per phase on the factory's bridge or micro-ohmmeter; phases compared with each other and with the design value | Unbalance between phases; value far from design, suggesting different wire or turns |
| Insulation resistance and HV test | Insulation tester reading, then the factory's high-voltage withstand test between windings and frame, witnessed and recorded | Low insulation resistance; breakdown or flashover |
| No-load run | Motor run at rated voltage and frequency; current, power and speed recorded and compared with the routine test sheet of the type | No-load current or power out of the factory's own band; noise or bearing rumble |
| Locked-rotor test | Rotor held, reduced voltage applied; current and power recorded where the factory's bench allows | Values far from the type, showing a rotor casting or winding fault |
| Load test and efficiency | On units we pick, on the factory's dynamometer or load bench, losses determined by the IEC 60034-2-1 method the bench supports | Measured efficiency below the declared value or the IE class limit |
| Vibration and noise | Vibration velocity measured on the bearing housings at no load and compared with the IEC 60034-14 grade ordered | Vibration above the grade limit |
| Dimensions | Shaft height, shaft diameter and length, keyway, foot hole centres and flange spigot measured against IEC 60072 or NEMA frame drawings; shaft runout with a dial gauge | Motor will not fit the driven machine or coupling |
| Nameplate, terminal box, earthing, IP | Rating plate read against the datasheet; terminal markings, earth terminal, cable gland entries and gaskets checked against the IP rating | Missing earth terminal; gasket missing on an IP55 motor; plate data wrong |
Efficiency class: the nameplate versus the test data
IEC 60034-30-1 defines international efficiency classes for line-operated AC motors, from IE1 upwards, by power, number of poles and frequency. IEC 60034-2-1 sets the methods for measuring the losses that efficiency is calculated from. A no-load run cannot show the class; only a load test with measured losses can.
In the EU, Regulation (EU) 2019/1781 has applied since 1 July 2021 to single- and three-phase induction motors from 0.12 to 1,000 kW. Three-phase motors from 0.75 kW up to 1,000 kW had to reach IE3 from July 2021, and motors between 75 and 200 kW have had to reach IE4 since July 2023, according to the European Commission's summary. The 2023 stage also brought in smaller and single-phase motors. Manufacturers must publish efficiency at several load points. Variable speed drives in scope must reach IE2.
In the US, general-purpose motors must meet the minimum nominal full-load efficiencies in 10 CFR 431 subpart B. The nameplate must show the nominal full-load efficiency and the Compliance Certification number DOE issues. Frame dimensions for the US market usually follow NEMA MG 1, not IEC 60072, so a motor built to IEC frames will not drop into a NEMA-framed machine.
On site, we compare the efficiency and class on the nameplate with the factory's load-test records for the units we witness and with the type-test report for the rating. Where the factory has no load bench, or you want independent figures, we seal motors for an accredited motor test laboratory through lab testing coordination. CE marking for motors rests on the Low Voltage Directive; US listing marks are covered on UL and ETL listing.
Common defects in electric motors
| Defect | Why it matters | Class |
|---|---|---|
| HV breakdown or very low insulation resistance | Shock and fire risk; early winding failure | Critical |
| No earth terminal, or earth not bonded to the frame | Frame can become live | Critical |
| IE class or efficiency on the nameplate not supported by test data | Motor cannot legally be placed on the EU or US market as marked | Critical |
| Phase resistance unbalance | Overheating and reduced life | Major |
| Shaft, keyway or mounting dimensions out of tolerance | Motor will not couple to the driven machine | Major |
| Vibration above the ordered grade | Bearing wear, noise, coupling damage | Major |
| Terminal box gasket or gland plugs missing | Water and dust enter; IP rating not met | Major |
| Paint runs, chips, nameplate rivet loose | Appearance and identification | Minor |
Packing, transit and your purchase order
Motors are heavy for their size and their bearings are the weak point in transit. Vibration on a truck or ship can mark the bearing races while the shaft stands still, so larger motors should have a shaft locking device, and machined shaft ends and flanges should be coated with rust preventive and covered. Small motors go in cartons on pallets; larger ones on skids or in crates, bolted down through the feet. The inspector checks the packing and lifting points, and that the terminal box is closed and cable entries are plugged.
Put these in your purchase order:
- Power, voltage, frequency, poles, duty, insulation class and temperature rise.
- Efficiency class and the standard it is to be measured by; market (EU, US, other) and required marks.
- Frame size and mounting to IEC 60072 or NEMA MG 1, with the outline drawing.
- Enclosure IP rating, cooling method, vibration grade and noise limit.
- Bearing make and type, terminal box position and cable entries.
- Routine tests to witness and how many motors are to be load tested.
- Type-test report and DOE or EU documentation to be supplied with the shipment.
Motors supplied as part of a pump set are covered on the pump inspection page. Book an inspection anywhere in India; Coimbatore is charged at actual travel cost (see pricing).
Sources
- Coimbatore district administration: Economy
- Department of Commerce, TradeStat: commodity-wise exports (HS 8501, FY2025-26 provisional)
- European Commission: Electric motors and variable speed drives, Regulation (EU) 2019/1781
- Commission Regulation (EU) 2019/1781 (EUR-Lex)
- 10 CFR Part 431 subpart B, Electric motors (eCFR)