Earthing is not needed for the motor to turn; it is there for the safety of people and the plant, so it must not be skipped just because the motor runs without it. When winding insulation weakens through moisture, vibration or heat, leakage can occur between a phase and the frame. If the frame is not earthed, that voltage sits on the metal surface and can injure anyone who touches it. With a proper PE connection, the fault current flows to earth and the fuse, circuit breaker or residual current device opens the circuit.

The HEM catalogue requires the protective earth (PE) connection to be continuous and low-impedance. In practice:

  • Connect the PE conductor to the earth-marked screw in the terminal box; if the frame has an additional earth point, use it as well.
  • Choose a cross-section compatible with the phase conductors and keep intermediate connections tight and clean.
  • In inverter systems, connect the screen of the shielded cable as recommended by the drive manufacturer.
  • Choose cable glands to suit the cable diameter and IP55 protection; close unused entries with blanking plugs.

Earth resistance and residual current device selection belong to the installation design; they must be measured and documented by a qualified electrician.