Specifying an AC motor in 2026 comes down to six engineering gates — power, speed, frame, efficiency, enclosure and duty — and a set of optional features (brake, feedback, insulation) layered on top [S1][S3].
AC machines split into single-phase and three-phase families, with induction (asynchronous) and synchronous as the two dominant rotor types; each branch has its own torque curve, starting method and typical duty envelope [S4][S5].
Power, Speed and Torque: The Mechanical Triangle
Rated mechanical output P (kW) and synchronous speed n = 120·f / p (with p = number of pole pairs) are the first two numbers any datasheet must show; torque T = 9550·P/n ties them together, so a 4-pole motor on 50 Hz mains sits at 1500 rpm synchronous, dropping to roughly 1430 rpm under full load on a standard induction design [S4].
For conveyor, fan and pump duty the torque curve is square-law or near-constant and a TEFC induction unit is the default pick; for press, hoist or high-inertia load the starting torque requirement typically pushes selection toward a high-slip or inverter-fed design with 150–250% starting torque capability [S3][S5].
Mounting, Frame and Mechanical Interface (IEC 60072)
B14 flange, B5 flange, B3 foot and the combined B35 foot-and-flange are the four IEC 60072 frame options that 95% of European and Chinese OEM catalogs default to; shaft height (56, 63, 71, 80, 90, 100, 112, 132, 160, 200, 225, 250, 280, 315, 355 mm) sets the centreline height and must be locked before a gearbox is selected [S1][S3].
SEW-EURODRIVE's gearmotor configurator exposes motor power (kW), output speed (1/min), gear ratio i and service factor fB as the four mandatory fields — fB > 1.0 is the safety multiplier on gearbox rating and should be ≥1.25 for cyclic, reversing or shock-loaded service [S3].
Efficiency Class: IE1 Through IE5 Under IEC 60034-30-1/2
International efficiency (IE) classes run IE1 (standard) → IE2 (high) → IE3 (premium) → IE4 (super-premium) → IE5 (ultra-premium, variable-speed only); the configurator in [S3] lists IE as a mandatory drop-down for every gearmotor quote, which mirrors the EU 2019/1781 + 2021 amendment regime that has effectively banned IE1/IE2 below 375 kW in European stock since 2023 [S3].
Specifying IE4 or IE5 typically adds 10–20% to unit cost but cuts rotor losses by 15–30% versus IE3; for continuous-duty S1 pumps, fans and compressors the payback usually lands inside 18 months on energy alone [S1][S3].
Enclosure, Cooling and IP Rating
Enclosure codes TEFC (totally enclosed fan-cooled), TENV (totally enclosed non-ventilated), ODP (open drip-proof) and TEAO (totally enclosed air-over) cover almost every industrial duty; pair with an IP code — IP55 is the default for dusty/wet industrial cells, IP65 for washdown food lines, IP66 for outdoor exposed mounts and IP68 for submerged or flooded-site service [S1].
Cooling method IC410 (free convection, no fan) is mandatory for inverter cabinets with limited airflow, IC411 (shaft-mounted fan) covers the majority of field installations, and IC416 (forced-vent) decouples cooling from shaft speed so a slow-running servo-driven machine still sheds full rated losses [S1][S3].
Duty Cycle: S1 Through S9 and Why It Drives Everything Else
IEC 60034-1 duty ratings S1 (continuous) through S9 (continuous with periodic load/speed variation) decide thermal derating; an S1 fan rated 22 kW may be the same frame as an S3 30% duty 15 kW hoist motor, but the latter cannot be operated continuously without tripping its winding thermostat [S1][S4].
For servo-driven packaging or machine-tool spindles, an S6 or S9 duty on a variable-speed drive lets the designer downsize the frame by 1–2 shaft heights versus a direct-on-line S1 unit at the same RMS load — see the Servo Drive vs AC Motor 2026 selection cut for the cross-axis trade [S1].
Voltage, Frequency, Insulation and Brake Options
Standard three-phase voltages cluster at 220–240 V Δ / 380–415 V Y for 50 Hz IEC markets and 230/460 V for 60 Hz NEMA; dual-frequency 50/60 Hz winding designs are common on Chinese OEM export stock [S1][S3].
Insulation classes B (130 °C), F (155 °C) and H (180 °C) define the hot-spot limit; in practice almost every modern stock motor ships as class F with class B temperature rise to leave 25 K thermal margin for inverter-duty voltage spikes [S1].
Spring-applied electrically-released fail-safe brakes in 24 V DC, 110 V AC or 220 V AC coil variants are the standard hold-and-stop add-on for hoists, conveyors and stage machinery; encoder feedback (incremental HTL/TTL, absolute Endat/Hiperface, resolver) is selected when the load is paired with a VFD closed-loop vector or a separate servo motor drive, see also the Servo Motor Selection 2026 spec gates reference [S3].
Where the AC Motor Loses — and When to Walk Away
AC induction is a poor fit where (1) torque must be held at zero rpm without encoder, (2) positioning accuracy below ±0.5° is mandatory, or (3) the duty cycle is high-accel / high-decel with cycle times under 200 ms — those cases fall to a servo motor or direct-drive linear motor instead, see the Servo vs Stepper Motor 2026 cut for the adjacent decision tree [S3][S4].
Explosive-atmosphere or dust-hazard sites add a hard gate: ATEX category 2/3 (zone 1/2 gas, zone 21/22 dust) certified Ex eb, Ex tb or Ex tc motors from IEC 60079-aligned catalogs must be specified, and the same machine should not be retrofit with a standard encoder without re-evaluating the certification scope [S1].
Comparison: Cage Induction vs Synchronous vs Inverter-Fed Vector
Three-phase squirrel-cage induction (lowest cost, 2–6% slip, soft-start via VFD), permanent-magnet or reluctance synchronous (IE5, wide constant-power range, needs encoder or self-sensing control), and inverter-fed vector induction (encoder + VFD, ~0.01% speed accuracy) cover the 2026 selection space; on the four decision axes of cost (lowest = cage), speed accuracy (highest = vector), constant-power speed range (widest = synchronous) and IE class ceiling (IE5 only synchronous/VFD), the cage design wins only on first-cost [S1][S3].
For project pipelines that also touch upstream/downstream cost, the Electric Motor Upstream and Downstream 2026 spec & cost map lays the supply-chain view, while cell-level line machinery and packaging follow a separate path that begins with the shrink-wrapping machine selection 2026 spec gates reference [S3].
Sourcing and Standards Reference
Lock the IEC 60034-30-1/2 efficiency class, IEC 60072 mechanical frame, IEC 60034-1 duty rating, IEC 60034-5 IP code and IEC 60034-11 thermal protection numbers on the purchase order before a unit price is discussed; Chinese OEM catalogs such as TITECHO expose kW, rpm, voltage, IE class, IP and insulation as standard line-item data on every variant [S1][S3].