Epoxy Coating Powders for Motor Armature Slot Insulation

Epoxy Coating Powders for Motor Armature Slot Insulation

One of the most popular applications for Epoxy Coating Powder is slot insulation for motor armatures. The main purpose of epoxy coating powders like the Linqsol MCP-5000 and Linqsol MCP-5260 is to create a barrier between steel lamination and the copper wiring. This process can be used for rotors inside a power generator, stator, and armature products. The motors can be for the automotive industry, or even power tools and home appliances.

Slot Liners vs Epoxy Coating Powders

motor armature with slot liners

Another popular method used for motor armature insulation is using slot liners and plastic castings. With this method, slot liners/plastic casings are inserted into the slot, providing the insulative barrier between the copper winding and magnetic core. A real-life example can be seen below:

Compared with slot liners and plastic casting methods, epoxy coating powders own the advantages of efficiency and reliability for multiple reasons:

  1. They allow the use of up to 25% more copper wire than plastic slot liners = increased efficiency by 15%-20%
space in epoxy coated motor armature versus slot lined motor armature

2. They provide a more even and consistent distribution = improved balance efficiency and lifetime

area where a motor armature gets epoxy coating powder

3. Since epoxy coating powders are 10x more thermally conductive than air, they can dissipate more heat from the motor = increased operating lifetime

graph showing thermal conductivity of air versus epoxy coating powder

Selecting Epoxy Coating Powders for Motor Armatures

To select the best epoxy coating powder for your motor armature, some of the requirements you need to take into consideration are:

  • Breakdown Voltage
  • Class Rating
  • Edge Coverage

Breakdown Voltage

Breakdown Voltage – Breakdown voltage is an electrical property that is thickness-dependent. It is the maximum amount of voltage that a dielectric material can withstand before breaking down. The breakdown voltage is calculated by multiplying the dielectric strength of the material times the thickness of the film. The higher dielectric strength will allow the material to achieve the same result with less material, translating into material cost savings.

MCP-5000 has a breakdown voltage of 25,000 V/mm, and MCP-5260 has a breakdown voltage of 30,000 V/mm.


Class – Another essential characteristic of epoxy coating powders for motor armatures is the class. Epoxy coating powders can be Class A (105°C), Class B (130°C), Class F (155°C), or H (180°C). The Class is calculated by looking at the maximum (hot spot) temperature at which the insulation can be operated and still have an average life of 20,000 hours. To calculate the maximum hot spot temperature, you take the ambient temperature, add it to the motor temperature rise, and then add the hot spot allowance. For example,

motor armature under infrared thermometer showing temperatures

Maximum Hot Spot Temperature =

  • Ambient Temperature: (57°C) +
  • Motor Temperature Rise (75°C) +
  • Hot Spot Allowance (5 – 15°C) (15°C)

      142°C Maximum Hot Spot Temperature

Motor Insulation Class Required: F

Insulation System / ClassMaximum Hot Spot Temperature (°C)
Table 1. Insulation System and Correlating Temperature

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.

Edge Coverage

Edge Coverage – One of the most important qualities of an epoxy coating powder for motor armatures is Edge Coverage. Since the parts are complex, with many edges and curves, the coating thickness on the sensitive parts must be high. The coating thickness must be higher because the copper wires at the edges are likely to cut through the coating powder, breaking the insulation barrier and shorting out the motor. That is why epoxy coating powders for motor armatures are specifically designed to have a higher edge coverage. A minimum 300-400um coating thickness and 40% edge coverage ratio are generally required. If high edge coverage is something you are looking for Linqsol MCP-5000 has an edge coverage of 55%.

microscope image showing edge coverage for epoxy coating powders


To sum everything up, the choice between epoxy coating powders and alternative methods, such as slot liners and plastic castings, for motor armature insulation is a crucial decision that significantly impacts motor performance. Epoxy coating powders, like Linqsol MCP-5000 and Linqsol MCP-5260, offer efficiency and reliability advantages by allowing increased copper wire usage and ensuring even distribution. Furthermore, their superior heat dissipation properties contribute to extended motor lifespans.

The selection process should consider factors such as breakdown voltage and class rating, where higher breakdown voltage translates to potential material cost savings, and the class rating determines the insulation’s operational temperature limits. Ultimately, carefully considering these factors is essential to optimize motor efficiency, lifespan, and overall performance in various industrial applications.

Facing challenges in product selection or encountering difficulties with your application? Let our team of Coatings Experts be your guide. Contact us today, and we’ll navigate the complexities with you to find the perfect solution for your unique needs.

About Kalliope Zembillas

Leave a Reply

Your email address will not be published. Required fields are marked *