Electric Motor Mounting Arrangements

Types of construction and mounting for industrial and marine machines — the IM Code (IEC 60034-7)

1. Overview and purpose

The mounting arrangement of an electric motor defines how the machine is mechanically attached to its foundation or to the driven equipment, and the direction in which its shaft points. It is as decisive to a successful installation as power, speed and efficiency: a motor that is correct on paper will not fit — or will not seal, lubricate and load its bearings correctly — if the mounting arrangement is wrong.

These arrangements are standardised internationally by IEC 60034-7 — Rotating electrical machines, Part 7: Classification of types of construction, mounting arrangements and terminal box position (IM Code). Standardisation lets motors from different manufacturers be described in the same language, ensuring interchangeability of frame, feet, flange and shaft.

The mounting code drives several downstream design choices, so it must be fixed early:

• Mechanical fit — feet spacing, flange spigot and bolt circle must match the base or driven machine exactly.
• Bearing selection and loading — a vertical shaft carries axial (thrust) loads differently from a horizontal one.
• Shaft sealing and lubrication — grease retention and seal design depend on whether the shaft points down, up or horizontal.
• Terminal box position and cable entry — critical in confined engine rooms and skid layouts.

2. The two designation systems

IEC 60034-7 provides two parallel systems. Both describe the same machine; nameplates and catalogues often carry both.

2.1 Code I — alphanumeric (the everyday code)

Written as IM (International Mounting), a space, a letter and one or two numerals — for example IM B3 or IM V1. The letter gives the shaft orientation:

• B = horizontal shaft (e.g. B3, B5, B14, B35).
• V = vertical shaft (e.g. V1, V3, V5, V6, V18). The numeral fixes the fixing method and the shaft direction (down or up).

2.2 Code II — all-numeric (the detailed code)

Written as IM followed by four digits — for example IM 1001. The leading digit signals the broad mounting family:

• 1xxx — foot-mounted arrangements (IM 1001 = B3).
• 2xxx — combined foot-and-flange arrangements (IM 2001 = B35).
• 3xxx — flange-mounted arrangements, no feet (IM 3001 = B5, IM 3601 = B14).

Related standards: IEC 60072-1 fixes flange and shaft dimensions; IEC 60034-5 covers IP degrees of protection. The former German standard DIN 42950 has been superseded by and aligned with IEC 60034-7. Rough NEMA equivalents are a rigid foot base (≈ foot), a C-face tapped flange (≈ B14/FT) and a D-flange with clearance holes (≈ B5/FF).

3. Common mounting designations

The most commonly occurring designations, grouped by mounting family, pairing each Code I designation with its Code II equivalent.

3.1 Foot-mounted

Code	IM B3	IM V5	IM V6	IM B6	IM B7	IM B8
Code II	IM 1001	IM 1011	IM 1031	IM 1051	IM 1061	IM 1071

3.2 Flange-mounted (large flange, clearance holes — type FF)

Code	IM B5	IM V1	IM V3
Code II	IM 3001	IM 3011	IM 3031

3.3 Flange-mounted with tapped fixing holes (type FT)

Code	IM B14	IM V18	IM V19
Code II	IM 3601	IM 3611	IM 3631

3.4 Foot and flange-mounted (combined)

Code	IM B35	IM V15	IM V36	—	—	—
Code II	IM 2001	IM 2011	IM 2031	IM 2051	IM 2061	IM 2071

IM 2051 / 2061 / 2071 are the combined foot-and-flange variants with the feet on the side or top (analogues of B6 / B7 / B8), and generally have no short Code I letter designation in common use.

4. Vertical arrangements

Vertical mounting is common for pumps and process equipment. Shaft direction (up or down) changes bearing and seal design, so it is always specified.

5. Flange types and dimensions

Flange-mounted motors use one of two flange families:

• Type FF (free / clearance holes) — the B5 / B35 large flange. Plain through-holes; bolted from behind the mating flange. Designated FF + pitch-circle diameter (e.g. FF165, FF265).
• Type FT (tapped holes) — the B14 small face flange. Threaded holes; bolted from the front. Designated FT + pitch-circle diameter (e.g. FT85, FT130).

Representative FF flange sizes (all dimensions in millimetres, per IEC 60072-1). Always confirm against the specific motor drawing before ordering.

Flange (FF)	M (PCD)	N (spigot)	P (outer Ø)	S (holes)	T (depth)
FF130	130	110	160	9	3.5
FF165	165	130	200	11	3.5
FF215	215	180	250	14	4
FF265	265	230	300	14	4
FF300	300	250	350	18	5
FF350	350	300	400	18	5
FF400	400	350	450	18	5
FF500	500	450	550	18	5

The flange number (e.g. FF265) refers to the fixing-hole pitch-circle diameter. B14 / FT flanges follow the same geometry with tapped rather than clearance holes and are generally used on smaller frame sizes.

6. Marine-sector considerations

Marine and offshore installations use the same IM Code but impose additional requirements that influence the mounting arrangement and the motor build behind it.

6.1 Classification-society approval

Motors for essential and emergency services on classed vessels must be type-approved and certified by the relevant society — DNV, Lloyd’s Register, ABS, Bureau Veritas, ClassNK, RINA, the Russian Maritime Register or CCS. Their rules set the environmental, inclination, insulation and testing requirements.

6.2 Inclination — heel, trim, roll and pitch

A ship is never a level foundation. Motors, and above all their bearing lubrication and any oil sumps, must keep working while the vessel is inclined and moving. Typical requirements (figures vary by society and service; emergency equipment is often more onerous) are of the order of:

• Static list (heel): about 15° to either side.
• Dynamic roll: about 22.5°.
• Static trim: about 5°.
• Dynamic pitch: about 7.5°, including combinations of the above.

Shaft direction and bearing/seal design therefore matter: grease retention and thrust handling differ markedly between a horizontal foot-mounted motor and a vertical flange-mounted one.

6.3 Where vertical (V1) mounting dominates

Vertical flange-mounted motors — most commonly IM V1 (flange up, shaft down) — are the norm for the many vertical pumps aboard ship: ballast, bilge, fire, cooling-seawater, cargo and general-service. Close-coupled B5 / B35 flange mounting is also common to guarantee alignment to a pump or gearbox.

6.4 Environment and protection

• Salt-laden, humid air and condensation: higher ingress protection (typically IP55 / IP56+) and anti-condensation heaters.
• Corrosion: marine-grade paint systems for higher corrosivity categories (e.g. C4 / C5-M) and tropicalised windings.
• Vibration and shock: robust arrangements such as B35 (foot + flange) favoured where both firm support and precise alignment are needed.
• Confined spaces: terminal box orientation chosen for practical cable entry.

7. Typical industrial applications

Arrangement	Typical use
IM B3	General-purpose workhorse: pumps, fans, blowers, compressors and conveyors on a bedplate or foundation.
IM B5	Close-coupled pumps and direct gearbox mounting where a concentric flange fit is required and floor space is limited.
IM B14	Small machines and pumps mounted directly to a machine face — compact drives, small gear units, machine tools.
IM B35	Heavier or higher-vibration duties needing both foot support and flange alignment — larger pump sets, gear drives.
IM V1	Vertical in-line and sump pumps, cooling-tower fans, process equipment with a downward shaft.
IM V5 / V6	Wall-mounted drives where floor mounting is impractical.
IM B6 / B7 / B8	Space-constrained installations where the motor sits on a wall or overhead rather than on its base.

8. Selection and ordering checklist

Confirm the whole mounting picture together before ordering:

1. Mounting code — Code I and, ideally, Code II (e.g. IM B35 / IM 2001).
2. Flange type and size — FF or FT, plus the flange number (PCD, spigot, outer diameter).
3. Shaft direction — horizontal, or vertical up/down (affects bearings and seals).
4. Shaft diameter and keyway — must match the coupling or driven component.
5. Frame size — evaluated together with the mounting.
6. Terminal box position — for cable entry and access.
7. Ingress protection and cooling — IP rating and cooling method (IC code) for the environment.
8. Marine only — classification society, inclination envelope, corrosion protection and certification.

9. Standards and references

• IEC 60034-7:2020 — Classification of types of construction, mounting arrangements and terminal box position (IM Code). Defines Code I and Code II.
• IEC 60072-1 — Dimensions and output series: frame numbers, flange (FF/FT) and shaft dimensions.
• IEC 60034-5 — Degrees of protection (IP code).
• DIN 42950 — former German mounting standard, superseded by / aligned with IEC 60034-7.
• Classification-society rules (DNV, Lloyd’s Register, ABS, Bureau Veritas, ClassNK, RINA, RMRS, CCS) for marine motor requirements.