Electric Motor Bearing

Ball bearing electric motor sizes by IEC frame

The ball bearing an electric motor uses follows its frame size more than its power rating, because the frame fixes the shaft diameter at the bearing seats. IEC frame numbers are the shaft centre height in millimetres, and makers fit similar deep groove ball bearings to similar frames. The table gives the sizes most often found at the drive end (DE) and non-drive end (NDE) of standard foot-mounted motors; individual makers differ, so confirm from the nameplate or manual before ordering.

Belt-driven motors often carry a larger 63 series bearing at the drive end, for example 6308 in place of 6208, because the belt pull adds radial load. Inverter-driven motors above a few kilowatts need a shaft grounding ring or an insulated bearing at one end; standard steel bearings are not insulated.

How to specify an electric motor bearing

Give the number as it appears on the old bearing: base number, closure suffix and clearance suffix, for example 6205 ZZ C3. If the marking is gone, measure bore, outside diameter and width and use the size finder. Motors nearly always call for C3 clearance because the inner ring is pressed onto a shaft that runs warmer than the housing; keep the group the motor maker chose. The full list is on the deep groove ball bearing page; the bearing supplier page shows every series with its bore range, and the bearing cross reference matches a number from another catalogue by size. We reply within 24 hours on business days.

• Base number: fixes d, D and B under ISO 15.
• Closure: ZZ for clean, fast positions; 2RS for dust and moisture; open where the housing is regreased.
• Clearance: C3 for most industrial motors; CN for small motors with light fits.
• Quantity per size and whether the two ends ship together.

Variants: open, ZZ or 2RS closures and C3 clearance on motor sizes

The same ball bearing electric motor size is listed in up to four versions, and the version is chosen by the motor housing rather than by the motor rating. Open bearings go where the end shield has a grease nipple and a drain, which is normal on larger frames. ZZ shields suit totally enclosed fan-cooled motors that run clean and are greased for life; they add almost no friction and keep the full speed limit. 2RS seals are the choice when the motor works outdoors, in agriculture, in washdown areas or in any position where the bearing sees water and fine dust, at the cost of a lower speed limit that matters only on 2-pole motors near the top of the range.

Clearance is written after the closure, so a shielded motor bearing with C3 clearance reads 6205 ZZ C3. The model page for each size lists the versions ENRO carries; if your motor calls for a version the page does not list, say so on the enquiry and the answer comes with the quotation. We reply within 24 hours on business days.