IS 325:1996 is the Indian Standard (BIS) for three phase induction motors. IS 325 is the primary specification for three-phase induction motors (the most common motor type) in India. It covers standard ratings from 0.18 to 315 kW, efficiency requirements, starting characteristics, temperature rise limits, and testing procedures. Referenced in pump, fan, and compressor specifications across all sectors.
Specification for three phase squirrel cage induction motors covering ratings, performance characteristics, testing, and marking for general purpose industrial use.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Three-phase squirrel-cage induction motors | Scope |
| Voltage/freq | 415 V, 50 Hz (standard LT) | Ratings |
| Output series | Standard kW ratings & frame sizes | Ratings |
| Efficiency | IE class (energy efficiency) per current norms | Performance |
| Tests | Temperature rise, locked-rotor, no-load, insulation | QC |
| Read with | IS 12615 (efficiency classes) / IS 900 / IS 732 | Cross-ref |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 325:1996 is the Indian Standard for Three-Phase Induction Motors — Specification. It is the flagship motor specification covering general-purpose squirrel-cage and slip-ring three-phase induction motors used across Indian industry.
Use it when: - Specifying motors for pumps, fans, blowers, compressors, conveyors, mills — the universal industrial workhorse - Procuring motors for HVAC systems, water-supply pumping stations, cement plants, steel mills, food processing - Auditing motor supply for nameplate accuracy, performance, energy efficiency - Selecting energy-efficient (IE-classified) motors per energy conservation regulations - Investigating motor failures — overheating, bearing failure, insulation breakdown
Companion codes: - IS 12615:2018 — Energy efficiency classification (IE1, IE2, IE3, IE4 — replaces older IS 12615:2004) - IS 8789:1996 — Single-phase induction motors - IS 13529:1992 — Standby duty motors - IS 12824:1989 — Inverter-duty motors for variable-frequency drive (VFD) operation - IEC 60034 (Parts 1-30) — International equivalent series
Three-phase induction motors are the most common electric motor type in industry, accounting for ~80% of industrial electricity consumption. Their efficiency directly impacts energy costs + carbon emissions. Modern energy-conservation regulations (BEE — Bureau of Energy Efficiency star ratings) mandate increasingly higher efficiency classes.
Two main types covered: 1. Squirrel cage motors (95% of installations): rotor with conductors short-circuited at ends; simple, robust, low maintenance. Operating speed = synchronous speed × (1 - slip), typically 0.5-5% slip. 2. Slip-ring (wound rotor) motors: rotor windings connected through slip rings to external resistors; allows variable speed + high starting torque control. Used for crane / mill / hoist applications; declining usage with VFD availability.
Frame size designation (per IS 1231:2011): combination of: - Frame number (50, 56, 63, 71, 80, 90, 100, 112, 132, 160, 180, 200, 225, 250, 280, 315, 355) — denotes shaft height in mm - Frame length code (S, M, L, A, B, C) — denotes body length
E.g., 'Frame 160 M' = 160 mm shaft height, medium body length.
Power rating (rated continuous mechanical output power in kW or HP): - Small motors: 0.37, 0.55, 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200, 250, 315, 355, 400 kW... - Large motors: 500, 630, 800, 1000, 1250, 1500, 2000, 2500, 3150 kW (less common; specialized)
Speed (synchronous speed, rpm): - 2-pole: 3000 rpm @ 50 Hz - 4-pole: 1500 rpm @ 50 Hz (most common) - 6-pole: 1000 rpm - 8-pole: 750 rpm - 10-pole / 12-pole: for low-speed applications (mills, crushers)
Operating voltage: - LV (Low Voltage): 415 V (typical Indian) up to 1000 V - MV (Medium Voltage): 3300 V, 6600 V, 11000 V (for motors > 150 kW typically) - HV (High Voltage): > 11 kV (very large motors; specialty)
Insulation class (Clause 5): - Class B: 130°C max temperature; older standard - Class F (modern standard): 155°C max temperature - Class H: 180°C max; for high-temperature applications
Most modern IS 325 motors use Class F insulation with Class B temperature rise — providing service life margin.
Enclosure (Clause 6): - TEFC (Totally Enclosed Fan Cooled): IP55 protection; standard for most applications - SPDP (Screen Protected Drip Proof): IP22 protection; for indoor sheltered - TEFV (Totally Enclosed Force Ventilated): for hazardous areas - TEPV (Totally Enclosed Pipe Ventilated): for very dusty / harsh environments - TEAO (Totally Enclosed Air Over): for fan-cooled applications where machine air-stream provides cooling
Duty type (Clause 7) — per IEC 60034-1: - S1: continuous duty (most common; runs at rated load indefinitely) - S2: short-time duty (typically 10-60 min cycles) - S3: intermittent periodic duty (start-stop cycles) - S4: intermittent with start period - S5: intermittent with start + electric braking - S6-S9: more specialized intermittent / variable patterns
IEC 60034-30-1 / IS 12615 efficiency classes:
Typical efficiency values (4-pole 50 Hz):
| Power (kW) | IE1 (%) | IE2 (%) | IE3 (%) | IE4 (%) | |---|---|---|---|---| | 1.1 | 75 | 80 | 84 | 86 | | 11 | 88 | 90 | 92 | 93.5 | | 75 | 92 | 94 | 95 | 96 | | 200 | 93 | 95 | 96 | 96.5 |
Economic analysis: - IE1 motor cost: baseline - IE2 motor cost: ~5-10% premium over IE1 - IE3 motor cost: ~15-25% premium over IE1 - IE4 motor cost: ~25-40% premium over IE1
Payback period: For a 75 kW motor at 6000 hours/year: - IE1 → IE2 efficiency improvement of 2% → energy saving = 75 × 0.02 × 6000 = 9,000 kWh/year - At ₹6/kWh = ₹54,000/year saving - Cost premium IE1 → IE2 ≈ ₹15,000 - Payback < 4 months; ROI excellent
For IE3, IE4: payback typically 1-3 years; very strongly economic for high-utilization motors.
Indian regulatory requirements: - BEE Star Labeling Programme (mandatory since 2014): retail / OEM motors must declare efficiency class - PAT (Perform Achieve Trade) cycles: large energy consumers required to upgrade to IE3+ motors - Green building standards (LEED, IGBC, GRIHA): credits for IE3+ motor usage
1. Specifying nameplate kW without margin — motors rated at 11 kW nominal will operate fine at 9-10 kW load but overheat + reduce life at 11+ kW continuous. Specify 10-15% margin (a 12.5 kW motor for an 11 kW continuous load).
2. Wrong insulation class for service environment — Class B insulation in hot ambient (Class F minimum needed in tropical industrial conditions) shortens life by 50%+. For tropical / outdoor / cement-plant / steel-mill applications, specify Class F at minimum.
3. Skipping IE3 / IE4 for hidden / continuous-run motors — applications like sewage pumping (24/7), large industrial fans, chiller compressors run >5000 hours/year. IE3 / IE4 motor cost premium is recovered in months; lifecycle savings huge.
4. No vibration analysis at commissioning — bearings + alignment errors cause vibration; vibration accelerates bearing wear; motor fails early. Mandate ISO 10816 vibration measurement at commissioning + periodically.
5. VFD operation without inverter-duty motor — variable-frequency drives produce voltage spikes + harmonics; ordinary motor insulation damages. Use inverter-duty motors (per IS 12824:1989) for any VFD application.
6. Wrong starter for the motor — DOL (Direct On Line) starter on > 22 kW motor: high inrush current (6-8× rated), voltage dip on supply system. Use star-delta starter or soft starter or VFD for larger motors.
7. Inadequate cooling — fan obstruction — IP55 motors have integral fan; if intake / outlet is blocked (by adjacent equipment, by debris, by mounting design), cooling is insufficient + motor overheats. Maintain clear 100-200 mm air space around motor cooling vents.
8. No earth-fault protection — earth-fault relay (ELR) or RCD essential for motor circuits in industrial environments. Without it, ground-fault causes catastrophic burn-out + safety hazard.
9. Single-phase running — if one phase loses connection (poor cable joint, blown fuse), 3-phase motor runs single-phase; severe overheating; insulation failure in minutes. Single-phasing protection relay essential.
10. Documentation lost — when a motor fails years later, the nameplate may be illegible, supplier records gone. Maintain digital motor inventory + asset register with original supplier, year of supply, rating, IS conformance, service / maintenance records.
IS 325:1996 is 29 years old but functionally aligned with IEC 60034 international practice. The 1996 revision (replacing IS 325:1978) updated terminology + efficiency requirements. Subsequent amendments incorporated energy efficiency classifications via IS 12615.
Indian motor market reality: - Major manufacturers (Siemens, ABB, KEC International, Bharat Bijlee, Crompton Greaves, Kirloskar, Hindustan Motors): consistent IS 325:1996 conformance, multiple efficiency classes (IE1-IE4), full range from fractional kW to multi-MW. Premium pricing but reliable quality. - Mid-tier manufacturers (numerous regional): variable quality. Quality assurance via factory audit + sample testing. - Imported motors (Siemens / ABB direct, Chinese / Korean brands): widely available; verify IS 325 + IS 12615 conformance for Indian regulatory compliance.
Procurement strategy by application: - High-utilization motors (> 4000 hours/year): always IE3 minimum; consider IE4 for premium applications - Pumping stations (water supply, sewage, irrigation): IE3 motors are now standard; cost recovered in 6-18 months from energy savings - Industrial process (mills, kilns, large fans): mostly IE3; IE4 for heavy-duty premium applications - HVAC: IE3 motors mandated by recent green-building specifications - Construction / temporary: IE1 / IE2 (low utilization; cost matters more than efficiency) - Crane / hoist / occasional duty: IE2 / IE3 depending on cycle
For specifying engineers: - Always specify: rated power, voltage, frequency, speed (poles), enclosure (TEFC / TEAO / etc.), insulation class (Class F), duty class (S1 typically), efficiency class (IE3 minimum) - For VFD applications: specify inverter-duty (IS 12824) - For hazardous areas: specify Ex-rated motors per IS 16290 / IEC 60079 - For premium applications: include vibration specification (ISO 10816 grade), noise level (typically < 80 dBA)
Cost reality (2026 typical Indian market): - 1 kW IE3 motor: ₹3,000-5,000 - 11 kW IE3 motor: ₹20,000-35,000 - 75 kW IE3 motor: ₹1,50,000-2,50,000 - 200 kW IE3 motor: ₹4,50,000-7,50,000 - 500 kW IE3 motor: ₹15-25 lakh - Pricing 15-25% lower for IE2 (where regulation allows); 15-30% premium for IE4
Quality assurance: - Manufacturer's BIS license + IS 325 + IS 12615 reference on nameplate - Performance test certificate (factory test) for each motor — efficiency, losses, no-load characteristics - Site testing: insulation resistance, no-load current, full-load current, voltage drop, vibration, temperature rise - Documentation: motor record + supplier certificate maintained for asset register
Future direction: - PMSM (Permanent Magnet Synchronous Motors): ~3-5% more efficient than IE4 induction motors; widely used for premium applications; some Indian manufacturers (Bharat Bijlee, Hindustan Motors) - VFD integration: integrated motor + VFD packages; growing market segment - Higher voltage motors: 11 kV, 22 kV, 33 kV motors for direct grid connection in large industrial; growing application - Smart motors: IoT-enabled monitoring; emerging
IS 325 remains the workhorse industrial motor specification in India. The market is mature; technology continues to advance; for any new motor procurement, IE3 minimum is now the practical standard.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Standard voltage | 415V, 50 Hz | 460V, 60 Hz | NEMA MG1 |
| Efficiency class | IE2/IE3 (BIS) | IE2/IE3 (IEC 60034-30) | IEC 60034-30 |