Motor Mounting Types B3, B5, B14 and B35 Explained for Oil-Free Compressor OEM Builds

Quick answer: B3 is foot mounted, B5 is a large flange with through-holes, B14 is a small flange with tapped holes, and B35 combines feet with a B5 flange. For oil-free compressor OEM builds, the code is chosen by base plate design, service removal path and cabinet volume rather than by motor efficiency.

B3 is a foot-mounted motor. B5 and B14 are flange-mounted: B5 uses a large flange with through-holes, B14 uses a small flange with tapped holes. B35 combines feet with a B5 flange. For an OEM building a compact oil-free compressor package, say a unit sized for a two-chair dental clinic, the mounting code comes down to the base plate, the direction the pump must slide out for service, and the volume inside the acoustic cabinet. Motor efficiency doesn't enter into it.

Where the codes come from, and why procurement teams rely on them

The letter-number designations are defined in IEC 60034-7, the international standard covering mounting arrangements and terminal box positions for rotating machines. Because the code describes fixing geometry rather than a specific brand, an OEM can specify B14 on a drawing and receive a motor that bolts to the same bracket pattern regardless of which compliant supplier builds it. That portability is the whole point: it takes the guesswork out of the interface between your cabinet and someone else's motor.

The four mounting types compared

Code	Fixing method	Typical use in a compressor package	Main trade-off
B3	Two feet bolted to a horizontal base plate	Base-plate builds, belt-driven modules, easy lift-out	Alignment depends on base plate flatness and shimming
B5	Large flange, bolts pass through motor flange into tapped bracket holes	Direct-coupled and belt builds needing concentric location	Larger flange footprint; bracket must be machined accurately
B14	Small flange with tapped holes; bolts pass through the bracket into the motor	Tight canopies and small face plates	Limited load capacity; small bolt circle
B35	Feet plus a B5 flange	Vertical or wall-mounted arrangements, thin base plates	Extra length, height and cost

Flange diameters, bolt circles and spigot registers vary by frame size and by model, so always confirm the actual dimensions on the manufacturer's dimensional drawing before cutting metal.

B3: foot mounted

The motor stands on two feet bolted to a horizontal surface. It is the simplest arrangement to install and the easiest to remove, which matters when a technician has to change a motor inside a crowded canopy. The catch is that the base plate becomes the alignment reference: if it is not flat and stiff, belt tension and pulley alignment drift over time.

B5: flange mounted, large flange with through-holes

Bolts pass through holes in the motor flange and thread into the machine or bracket. A machined register (spigot) centres the motor, giving concentric alignment that suits direct-coupled and belt-driven oil-free modules where pulley runout must stay small. The bracket must be rigid. A flange bolted to a thin sheet-metal panel will transmit vibration straight into the acoustic enclosure.

B14: flange mounted, small flange with tapped holes

The motor carries a smaller flange with threaded holes; bolts pass through the bracket into the motor face. This is the compact option, common where the compressor module hangs off a small face plate inside a narrow cabinet. Load capacity and bolt size are correspondingly smaller, so it suits lighter motors rather than large frames.

B35: feet plus B5 flange

B35 gives you both: the feet carry the weight and the flange locates the shaft. It is useful when a thin base plate cannot provide reliable support on its own, or when the motor sits vertically. The penalty is added length and height, plus a more complex bracket, so it is usually reserved for builds that genuinely need dual fixing.

Use B3 when the base plate is the reference surface and the motor must lift out easily. Use B14 when the cabinet only offers a small face to bolt to. Use B35 when you need location and support at the same time.

Why the mounting choice matters more on an oil-free compressor

Oil-free compression modules are typically enclosed in an acoustic canopy, which compresses the design envelope and raises the cost of getting the interface wrong.

• Flange mounting fixes the centre distance between motor and compression module, so belt tension stays stable across service cycles. Foot mounting leaves that distance dependent on how well the base plate was machined and shimmed.
• A rigidly flanged motor couples vibration directly into the panel it is bolted to. Feet sitting on anti-vibration pads decouple the motor from the cabinet, which usually helps when the noise target is tight.
• Decide which direction the motor and pulley guard come out before you drill the base plate. A flange-mounted motor inside a closed canopy can be effectively trapped if the removal path was never dimensioned.
• Feet raise the motor above the base plate, leaving room for drain routing and airflow underneath. A flange mount can put the motor body low in the cabinet, where condensate trays and drain lines compete for the same space.

Applying it: an OEM package for a two-chair dental clinic

Take a realistic OEM scenario: you are building a compact oil-free compressor package for a two-chair dental clinic, running on a single-phase 220–240 V supply, with the receiver and dryer tucked into the same acoustic cabinet. The clinic's room is small, so cabinet volume and noise are the tightest constraints, and both are shaped by the motor mounting decision. Our buying guide for a small clinic covers the demand side of that specification; the mounting question sits on the supply side, where your cabinet drawing meets the motor.

Cabinet volume is the binding constraint

In a two-chair package, every litre of cabinet space is contested by the receiver, dryer, filtration and the compression module. A B14 flange lets the motor sit tight against a face plate and saves the floor area that feet would occupy. If the layout allows a slightly deeper base plate, B3 usually wins on serviceability and cost.

Decide the removal direction before the base plate

Sketch the service access first: motor out the front, out the top, or out through a removable side panel. Flange mounting only makes sense if the mounting face is on the same side as the removal path. On many compact dental packages, a B3 motor on a shallow pedestal is faster to swap than a flange motor buried behind the dryer.

Noise targets shape the mounting, not the motor

If the clinic expects the compressor to sit near the treatment rooms, vibration transmitted through a rigid flange into thin panels will add structure-borne noise that the canopy insulation cannot absorb. Feet with isolation pads, or a B35 arrangement on a stiffened bracket, generally give the acoustic engineer more to work with.

Keep the electrical interface on the same drawing

Voltage, frequency, phase and terminal box position should appear on the same drawing as the mounting code. A terminal box that ends up facing the cabinet wall forces a cable route change late in the build, which is a small error with an expensive fix.

Procurement checklist before you release the base plate drawing

• Mounting code stated explicitly on the drawing, not inferred from a datasheet photo
• Flange register diameter, bolt circle, hole count and thread verified against the bracket
• Foot hole spacing and base plate thickness checked so bolts do not bottom out
• Shaft orientation, shaft end and rotation direction confirmed
• Removal path dimensioned for motor, pulley and belt guard together
• Isolation pads or anti-vibration mounts specified wherever panels are thin
• Terminal box position and cable gland clearance confirmed
• Voltage, frequency and phase documented alongside the mounting data

For a fuller electrical and mechanical sign-off sequence, see our seven-step electric motor checklist for a two-chair dental clinic.

Working with Shenron on the mounting detail

Shenron supplies oil-free air compressors and can review your mounting arrangement against the cabinet drawing before the base plate is machined. Send the mounting code, shaft orientation and available envelope; final flange and foot dimensions should always be confirmed on the dimensional drawing for the specific model, because frame sizes differ between models. Browsing the oil-free air compressor range is a reasonable starting point for matching cabinet size to capacity before the mechanical interface is fixed.

Frequently Asked Questions

Is B35 the same as B3 plus B5?

In practice, yes. B35 combines two feet with a B5 large flange, so the motor is supported by the feet and located by the flange. It is chosen when a thin base plate cannot hold alignment on its own, or when the motor is mounted vertically.

Can a B5 motor be swapped for a B14 without changing the bracket?

No. B5 and B14 differ in flange diameter, bolt circle and fixing method — B5 uses through-holes in the motor flange, B14 uses tapped holes. A swap needs a new bracket or an adapter plate, and usually a different frame size.

Which mounting suits a compact two-chair dental compressor cabinet?

B14 is often the space-efficient choice where the motor must bolt to a small face plate inside the canopy. B3 remains the better option whenever the layout allows a base plate and a clear lift-out path, because service access matters more than a few centimetres of footprint.

Does the mounting type affect compressor noise?

It affects the vibration path, which in turn affects structure-borne noise. A rigid flange bolted to a thin panel transmits more vibration than feet resting on isolation pads, so mounting and cabinet stiffness should be decided together.

What must an OEM give the motor or compressor supplier?

The mounting code, frame size, shaft orientation and rotation direction, available envelope, and the electrical supply details. Supplying the cabinet drawing alongside these points removes most of the ambiguity that causes rework.

The short version

Mounting codes are an interface specification, not a marketing feature. Fix the service removal path and the base plate stiffness first, then let those two constraints pick between B3, B5, B14 and B35. Lock the choice onto the drawing before any sheet metal is cut.

OEM mounting checklist before releasing the base plate drawing

• Mounting code stated explicitly on the drawing, not inferred from a datasheet photo
• Flange register diameter, bolt circle, hole count and thread verified against the bracket
• Foot hole spacing and base plate thickness checked so bolts do not bottom out
• Shaft orientation, shaft end and rotation direction confirmed
• Removal path dimensioned for motor, pulley and belt guard together
• Isolation pads or anti-vibration mounts specified wherever panels are thin
• Terminal box position and cable gland clearance confirmed
• Voltage, frequency and phase documented alongside the mounting data

Motor mounting codes compared for compressor OEM builds

Code	Fixing method	Typical use	Main trade-off
B3	Two feet bolted to a horizontal base plate	Base-plate builds, belt-driven modules, easy lift-out	Alignment depends on base plate flatness and shimming
B5	Large flange, bolts through motor flange into tapped bracket holes	Direct-coupled and belt builds needing concentric location	Larger flange footprint; bracket must be machined accurately
B14	Small flange with tapped holes, bolts through bracket into motor	Tight canopies and small face plates	Limited load capacity; small bolt circle
B35	Feet plus a B5 flange	Vertical or wall-mounted arrangements, thin base plates	Extra length, height and cost