On HEM motors the squirrel-cage rotor is dynamically balanced to G2.5 / G6.3 quality, and the standard vibration reference under ISO 10816/20816 and IEC 60034-14 is about 1.8 mm/s or less. If vibration measured on site is clearly higher, the cause is usually outside the motor. The catalogue's troubleshooting table lists these causes:

  • Misalignment: the motor and machine shafts are not on the same axis; the coupling and bearings are strained.
  • Loose mounting: foot bolts, base or flange connection not tight enough, or one foot not seated fully on the base.
  • Pulley or coupling imbalance: a part fitted to the shaft afterwards is out of balance.
  • Bearing wear: vibration comes with rising noise and temperature.

A good first step in diagnosis is to uncouple the motor and run it at no load. If vibration is low at no load, the source is the driven machine, the coupling or the alignment. A weak base or a thin sheet-metal frame can also amplify vibration at certain speeds. Not hammering couplings or pulleys onto the shaft is important for protecting the bearings. For base compatibility, see the motor selection and mechanical fit questions page.