Motor armatures

Motor Armatures

Coil winding insulation

Up to Class H insulation class

Slot insulation

An electric motor is made by wrapping an electric current around a magnetic core, and these two must be insulated from each other.  This can be done in two ways.

First and most tried and proven way is to use slot liners and plastic casing. The slot liners are used for insulation and the plast case is needed to hold those liners together. This is mainly used by low end motor manufacturers.

The second and much more modern and efficient way is to use insulating epoxy coating powders. The powders are electrostatically deposited in the slot and then cured. These powders are highly insulative and with their ability to coat thick they have good edge coverage and excellent electrical insulation.

The removal of papers and plastic also allows for more space for coil and hence efficiency. You can use 25% more copper wire and the motor becomes much quieter. To add to that, the powders are highly thermally conductive, resulting in much better heat dissupation and an inevitable increase in the operating lifetime.


Motor armature insulation classes

The motor’s insulation class is the maximum (hot spot) temperature at which the insulation can be operated and still have an average life of 20,000 hours. The Rule of Thumb is that a 10°C rise cuts the insulation's useful life in half and a 10°C decrease doubles the insulation's life.


Insulation System



Hot Spot Temperature (°C)









Depending on where the motor is going to be used, Class B should be sufficient for 95% of the applications. There are some applications such as ABS motors or Power closure motors that require Class H insulation but these are the exception to the rule.


Epoxy Coating Powders for Slot Insulation of Motor Armatures

Tailor-Made Coating Powders

Over the years, SolEpoxy has developed two important epoxy coating powders. The first epoxy coating powder is used on automotive “enclosure” motors, window lift motors and wiper motors. The second epoxy coating powder was specifically developed for fuel pumps.

DK7-0953M for Coil Winding Applications

DK7-0953M is a light blue coating powder for rotors and stators within Motor Armatures. This epoxy coating powder is used extensively by one of the biggest suppliers in the world of electric windows, wiper motors, and electric seat adjustments. This epoxy coating powder gives a beautiful result when coating using an Electrostatic Fluidized Bed coating machine. To our knowledge, it has the best edge coverage of all manufacturers of functional coating powders, which is very important for these applications.

DK15EG-05 for Contact with Automotive Fluids

DK15EG-05 is available in either black or green color and is a “solvent resistant” coating for smaller rotors and stators. This epoxy coating powder was tailor-made for a major, Tier 1 automotive supplier of car and mini-van fuel pumps. In addition to the excellent edge coverage, the DK15EG-05 is resistant against a range of automotive fluids including gasahol. It can also be used as an alternative to DK7-0953M if customers need specifically a black- or green-colored epoxy coating powder.