The mounting form determines how a motor is fitted to your installation, feet, flange, or a combination. Choose wrong and mechanical fitment fails or you pay for features you don't need. This guide explains the main IEC mounting forms, typical applications, and the price differences.
Available from stock at Van Bodegraven. Stock in Dordrecht, Piraeus, Singapore and China; shaft, flange, terminal box and coating are adapted where needed in our own workshop. Typically delivered from stock within 1 to 5 working days.
The five most common mounting arrangements
B3, foot-mounted
The motor stands on feet cast or riveted to the housing. The load is carried by the foundation structure.
- Use: free-standing installations with belt or coupling drive, compressors, pumps with their own bearing housing.
- Advantage: simple installation, easily accessible for maintenance.
- Drawback: must be aligned accurately with the driven machine; misalignment causes bearing damage.
B5, through-bolted flange
The motor is mounted on a flange at the drive end; bolts pass through the flange into the driven machine or gearbox. No feet.
- Use: direct connection to pumps, fans, gearboxes.
- Advantage: no additional alignment needed if the flange fits cleanly against the driven machine; compact.
- Drawback: all load is transferred through the flange; not suitable for large radial loads.
B14, face-mounted with tapped holes
Like B5, but the mounting holes in the flange are tapped; bolts are inserted from the machine side.
- Use: smaller gearboxes, pumps, drives where the back of the flange is not accessible.
- Advantage: mounting possible from one side.
- Drawback: only suitable for smaller motors (usually up to frame 160).
V1, vertical, shaft down
Motor stands vertically with the shaft pointing down, usually with the flange on top. Widely used for submerged pumps, mixers and immersion pumps.
- Use: cooling towers, cast-iron pumps in process channels, vertical well pumps.
- Advantage: compact footprint.
- Drawback: the axial load on the bearings must precisely match the application.
Combi B3/B5 (feet + through-bolted flange)
The motor has both feet and a through-bolted flange. This provides flexibility.
- Use: OEM machine building where the motor can be mounted in different mechanical configurations.
- Advantage: maximum flexibility when the final mounting is uncertain.
- Drawback: slightly higher motor cost; sometimes a little larger.
The key dimensions
When ordering a replacement, you need these dimensions in addition to the mounting arrangement:
| Code | What | Why it matters |
|---|---|---|
| H | Shaft height (centreline to foot sole) | Determines frame size (IEC 80, 90, 100, etc.) |
| D | Shaft diameter | Coupling size |
| E | Shaft extension length | Needed for coupling positioning |
| F | Key (keyway dimension) | Coupling key size |
| P | Flange diameter (outside) | Does the motor fit the existing flange opening? |
| N | Flange spigot diameter | Alignment |
| M | Pitch circle diameter (PCD) of bolts | Location of mounting holes |
| A, B | Foot spacings | For B3 mounting |
| L | Overall motor length | For the space check |
The best way to send all required information in one go with a replacement request is our Dimension Sheet, where all fields are already structured for you.
Converting between mounting arrangements
Sometimes you have a B3 motor but need a B5 mounting, or the other way around. Three options:
1. Order a combi B3/B5 motor
Virtually all manufacturers (ABB, Dormot) supply combi versions. The premium over B3-only is typically 10-15%. If you are not sure at the time of the request what the final mounting will be, choose combi by default.
2. Convert in our workshop
For specific motors we can convert a B3 motor to B5 in Dordrecht (fitting a flange) or vice versa. This requires precise mechanical work and is carried out by our engineers with controlled flange tolerances. Typical lead time: 3-5 working days.
3. Use an adapter flange
An intermediate flange that puts the B3 motor onto a B5 mounting. This is a fast, low-cost solution but does introduce extra axial space. Not suitable where the dimension is critical.
If you buy motors for a machine line where the final mounting method is only fixed in the last engineering meeting, order combi B3/B5 as standard. That prevents having to make mounting modifications after purchase.
Summary
- B3: foot-mounted, standard for belt or coupling drive.
- B5: through-bolted flange, for direct mounting on pump or gearbox.
- B14: smaller tapped flange, for single-side mounting.
- V1: vertical, for submerged and well pumps.
- Combi B3/B5: maximum flexibility for OEM applications.
- When in doubt, order combi, the premium is limited, the flexibility large.
- Fill in our Dimension Sheet for a replacement, then you never have to worry about forgetting something.
No rights can be derived from the information in this article. Contact us for a concrete quotation and current delivery status.
Not sure which mounting arrangement?
Fill in our Dimension Sheet with as much data as you have, or send a photo of the existing motor, and our engineers will determine the right mounting arrangement for your application.