In most cases keeping it pays off, but turning the frame back into a running motor is not always the right call. A sound frame is valuable for checking the dimensions of the new motor, holding parts such as the end shield, fan and terminal box as spares, or setting it aside to be rewound later.

DRG-160L-2 18.5 kW 3000 rpm cast iron frame DRG three-phase motor – burnt-out motor frame

What does a sound-looking frame not prove?

When a winding burns out, the real risk lies where you cannot see it. The stator core may have been affected by excessive heat and the insulation between the laminations may have broken down; the processes used to strip the old winding can also weaken that insulation. As a result, the rewound motor may run hotter. Cracks in the rotor bars, ovality of the shaft journals and wear in the bearing housings must also be measured separately. This inspection is done by a rewinding workshop; deciding from the outside is misleading.

Three ways to use a stored frame

  1. Dimensional reference: When buying a new motor, the shaft diameter, foot holes and flange are measured directly on the old frame.
  2. Parts bank: The fan, fan cover, terminal box lid and cable gland can be reused on motors of the same frame size.
  3. Second motor: If the workshop report is favourable, it is rewound and kept as a standby, so the line stops for a shorter time at the next failure.

The cost of keeping it

In a damp store, the bearings of an idle frame rust and the core oxidises. It needs a dry, covered place and a labelled record. Moreover, rewinding and refitting the same frame without finding out why it burnt out can bring back the same failure: phase loss, overload or a blocked cooling path must be dealt with first.

Having a DRG motor that is still under warranty opened or rewound by an unauthorised party ends the warranty; for such a motor, a warranty claim should be made first.

Comparing with a new motor

The rewinding cost, workshop time and core risk should be weighed against a new motor of the same size. For comparison, see the dimension page of the 11 kW 1000 rpm DRG-160L-6 cast iron model or the three-phase asynchronous motor family.