An IEC motor frame designation looks simple and mostly is, once you know that the number is a dimension cue. Unlike a NEMA frame number, which is a coded value, an IEC frame number is normally read as shaft centre height in millimetres. The letter after the number sets body length, and a mounting code (B3, B5, B14, B35) describes the mounting arrangement.
This guide explains the source-aware limits behind the IEC Motor Frame Decoder: frame series, S/M/L length logic, common mounting labels, 2-pole shaft-diameter caveats, and why an IEC-to-NEMA cross-reference is a nearest reference, not a drop-in replacement or purchasing approval.
1. How to Read an IEC Frame
The number is the shaft centre height in millimetres: the distance from the bottom of the mounting feet to the centre of the output shaft. IEC 60072-1 sets this. So a 132 frame has a 132 mm shaft height, a 160 frame has 160 mm, and so on through the series 56, 63, 71, 80, 90, 100, 112, 132, 160, 180, 200, 225, 250, 280, 315, 355.
The letter after the number is the body length: S (short), M (medium), or L (long). On the small frames (63 to 80) you may see A, B, or C instead. The length letter changes the foot spacing (the axial B dimension) and the rating band, not the shaft height. So 132S and 132M have the same 132 mm shaft height but different foot spacing, and they are not interchangeable on a fixed base without slotting the feet.
A mounting suffix (B3, B5, B14, B35) describes how the motor mounts, and it is independent of the frame size. The decoder parses it separately, so "160M B35" returns both the 160M frame and the B35 foot-and-flange mounting.
2. The Frame Series, Shaft Height, and Shaft Diameter
| IEC frame | Shaft height (mm) | Shaft dia D (mm) | Typical 4-pole (kW) | Nearest NEMA |
|---|---|---|---|---|
| 71 | 71 | 14 | 0.37 | NEMA 42 |
| 80 | 80 | 19 | 0.75 | NEMA 48 |
| 90S / 90L | 90 | 24 | 1.1 / 1.5 | NEMA 56 |
| 100L | 100 | 28 | 2.2 to 3.0 | 145T |
| 112M | 112 | 28 | 4.0 | 184T |
| 132S / 132M | 132 | 38 | 5.5 / 7.5 | 213T / 215T |
| 160M / 160L | 160 | 42 | 11 / 15 | 254T / 256T |
| 180M / 180L | 180 | 48 | 18.5 / 22 | 284T / 286T |
| 200L | 200 | 55 | 30 to 37 | 326T |
| 225S / 225M | 225 | 60 (55 at 2-pole) | 37 / 45 | 364T / 365T |
| 250M | 250 | 65 (60 at 2-pole) | 55 | 405T |
| 280S / 280M | 280 | 75 (65 at 2-pole) | 75 / 90 | 444T / 445T |
Two things in this table catch people. First, on frames 225 and larger, the 2-pole (roughly 3000 RPM) build can use a smaller shaft than the 4-pole and slower builds. Use the actual motor drawing before selecting a coupling or bushing. Second, the typical kW is typical, not fixed: IEC does not bind power to frame, so efficiency class, product family, speed, enclosure, and manufacturer selection can move the rating.
IEC Motor Frame Decoder
Decode IEC motor frames to shaft-height and NEMA cross-reference cues, with warnings for standards, drawings, and fit review.
3. The S, M, and L Length Letters
The length letter is the part most people skip, and it costs a second trip when they do. The letter sets the body length, which sets the foot spacing (the B dimension, measured along the motor axis between the foot bolt holes). The shaft height (the number) stays the same.
- 132S has a foot spacing of B = 140 mm.
- 132M has a foot spacing of B = 178 mm.
Both are 132 mm shaft height, but a base drilled for 132S may not line up with a 132M without adapter work. When a drawing or parts list says just "132", it is ambiguous: it could be 132S or 132M. Read the exact letter off the nameplate and verify the base pattern before ordering a slide base or cutting a mounting plate. The decoder, given a bare "132", shows 132M as the representative and lists 132S so you know both exist.
4. Mounting Codes: B3, B5, B14, B35
The mounting code comes from IEC 60034-7 and describes how the motor attaches. It is orthogonal to the frame size.
| Code | IM code | What it is |
|---|---|---|
| B3 | IM B3 (IM 1001) | Foot-mounted, horizontal shaft. The default industrial mounting. |
| B5 | IM B5 (IM 3001) | Flange-mounted, large clearance flange (FF type) with through-holes. No feet. |
| B14 | IM B14 (IM 3601) | Face-mounted, small flange (C-DIN type) with tapped holes. No feet. |
| B35 | IM B35 (IM 2001) | Foot-mounted with a B5 flange added. The common foot-and-flange combination. |
The two flange types matter for a swap. B5 is the large flange with clearance holes (bolts pass through the flange into the driven machine). B14 is the small flange with tapped holes (bolts come from the driven machine into the flange). They are not interchangeable. A B35 motor has both feet and a B5 flange, so it can mount either way.
5. IEC to NEMA Is Nearest, Not a Drop-In
The cross-reference between an IEC frame and a NEMA frame is approximate, and the decoder repeats this because it is the rule that gets ignored. An IEC frame and its nearest NEMA frame have similar shaft heights, but the shaft diameter, the keyway, the foot bolt pattern, and the bolt-hole diameter all differ between the metric and imperial systems.
The shaft-height gap shows how close the match is. IEC 90 is 90.0 mm; NEMA 56 frame and 143T/145T are 3.5 inches, which is 88.9 mm, a 1.1 mm gap. That is a close match on height. But IEC 100L maps to NEMA 145T with about an 11 mm gap, because the chart is matching on power and mounting overlap there, not on shaft height. Either way, the shaft diameter and bolt pattern still differ, so a physical swap needs an adapter base or re-drilled feet and usually a different coupling or bushing for the shaft.
NEMA puts it the same way in its own guidance: the two frame systems land generally within a few millimetres on shaft height but are not interchangeable. Use the cross-reference to find the right NEMA frame to look for, then plan the adapter, not a bolt-in.
6. Using the Decoder With This Guide
Open the IEC Motor Frame Decoder and type any IEC frame ("112M", "132S", "90L") or a bare height ("132"). The decoder returns the shaft height, the shaft diameter with the 2-pole value where it applies, the foot spacing, the typical power by pole count, the parsed mounting code, and the nearest NEMA frame with the shaft-height gap. Enter a NEMA frame instead ("213T", "256T") and it runs in reverse.
When it finds a NEMA frame, it deep-links into the Motor Nameplate Decoder with that frame pre-loaded so you can screen the NEMA-side context separately. PDF and CSV export carry the decode, warnings, assumptions, and source pointers, and the URL is shareable for review.