IEC Motor Frame Sizes — Shaft and Mounting Dimensions 63 to 315
Standards explainer compiled by cBallast. 3-page PDF; the full content is on this page.
Compiled by
cBallast
Subject
Electric motors
Document type
Standards explainer
Reference
2026 edition
Issued
2026-10-18
Pages
3
Format
Web page and PDF
The IEC frame number decoded (it is the shaft height in millimetres), the standard shaft diameter and key per frame, B3 foot, B5 flange and B14 face mounting explained, typical 4-pole power per frame for sanity checks, and the replacement checklist that keeps a motor swap to one shutdown.
The frame number is a dimension
An IEC frame designation like 132M states the shaft centre height above the feet in millimetres — the one dimension everything else hangs on. Letter suffixes (S/M/L) vary foot spacing within the height. Standard shaft and typical 4-pole ratings line up like this:
Frame
Shaft Ø × length (mm)
Typical 4-pole kW
63
11 × 23
0.12–0.18
71
14 × 30
0.25–0.37
80
19 × 40
0.55–0.75 — the stocked 0.75 kW B5 motor is the textbook 80-frame
90
24 × 50
1.1–1.5
100
28 × 60
2.2–3
112
28 × 60
4
132
38 × 80
5.5–7.5
160
42 × 110
11–15
180
48 × 110
18.5–22
200
55 × 110
30
225
60 × 140 (4-pole)
37–45
250
65 × 140
55
280
75 × 140
75–90
315
80 × 170
110–160
Keys follow DIN 6885 per shaft size; 2-pole motors from frame 225 up may carry a reduced shaft. The kW column is a sanity check, not a law — manufacturers shift ratings between adjacent frames with efficiency class (IE guide: IE3/IE4 motors sometimes grew a frame against old IE1 equivalents).
Mounting letters
B3 — foot-mounted: match frame height and foot hole pattern.
B5 — large flange with through-holes, carried on the flange: match flange PCD and spigot.
B14 — smaller face with tapped holes for gear units and pump heads.
Combination forms (B35 = feet + B5 flange) are common on stock motors — e.g. the stocked 3 kW IE3 IP55 and 11 kW units in the ventilation line.
Replacement checklist
Frame + suffix and mounting letter off the old plate; shaft Ø/length confirmed with a caliper (reduced-shaft 2-pole traps live here).
kW, poles/rpm, voltage/frequency and duty class (S1–S10 guide); efficiency class per the regulation in force at the installation.
IP rating and insulation/ambient; drive end fit — coupling hub bore (coupling guide) or pulley taper bush.
VFD duty noted when applicable — see the VLT guide for the drive side.
Over 3,000 motor line items are quotable; the plate photo plus shaft measurement is the complete enquiry, answered within 24 hours.
Frequently asked questions
What does frame 132 mean on a motor?
The shaft centreline sits 132 mm above the mounting feet — the IEC frame number is that height in millimetres, with S/M/L varying the foot spacing. A 132 frame carries a 38 mm shaft as standard.
Are IEC and NEMA frames interchangeable?
No — NEMA numbers encode shaft height in quarter-inches with different foot and shaft tables. Converting an installation across systems means adapter plates or machining; matching within IEC is the clean path, and the chart above is IEC only.
Can a B5 motor replace a B3?
Only with a mounting change — B5 hangs on its flange, B3 stands on feet. B35 (feet plus flange) motors cover both and are the stock-keeping trick; specify the combination form when either could recur.
Why is the new IE3 motor bigger than the old motor it replaces?
Higher efficiency classes carry more active material; some ratings moved up a frame size against old IE0/IE1 designs. Check frame and shaft before assuming like-for-like on 20-year-old installations.
Which dimensions must match for a drop-in motor swap?
Frame height and foot/flange pattern, shaft diameter and length, and the terminal-box orientation you can live with — plus the electrical data. Everything else (make, series) is negotiable; those dimensions are not.