Electrical Insulation Material Selection Considerations

A guide to the specification of insulation materials

One of the first things an electrical engineer learns is that the number one enemy in the design and manufacture of any electrical/electronic product is heat. It's the one feature that can transform your idea of ​​a handheld device into a desktop device. When talking to a manufacturer about insulation, the first question that comes up is temperature resistance. This is a very important trait, but there are a few others that also need to be considered. In addition to temperature resistance, voltage and mechanical strength also play a very important role in the selection of insulation.

In the electrical appliance industry there are different temperature classes, which are divided into classes (see table). These classes are a standard established by the National Electrical Manufacturers Association (NEMA). At the lowest end is insulation class A. This entry-level insulation class has a nominal temperature of 105 °C, an average winding temperature rise of 55 °C, a hot spot temperature rise of 65 °C and a maximum winding temperature of 105 °C due to the insulation rating of 105 °C. The temperature classes in ascending order include class B at 130 °C, class F at 155 °C, class H at 180 °C, class N at 200 °C and class R at 220 °C. For each of these classifications, there are different insulation materials that are best suited to meet the desired insulation class.

VOLTAGE
Once you've chosen your temperature class, you can move on to the next important characteristic: the voltage. This is where you start to really separate the isolation options and start prioritizing the options available for your particular application. Most know that 125 volts is the standard voltage for homes and most know that 220 volts is the voltage for many domestic dryers. These are just two of the many different voltages used in the electrical appliance industry. When you start to really research how many different voltages there are, you will be very surprised. Some of the main voltages used in electrical equipment are 12V, 24V, 125V, 208V, 220V, 460V, 575V, 950V, 2300V, 4160V, 7,5kV and 13,8 kV. So as you choose your voltage requirements, the choice of insulation becomes smaller and smaller.

MECHANIC SOLIDITY
Now that you have selected these two primary properties—temperature and stress—you can turn to mechanical strength. This is particularly important for flexible insulation and adhesive tapes. Flexible insulation is z. B. used in electric motors to isolate the metal core of the stator from the magnet wire. If the current in the magnet wire exceeds the strength of the flexible insulation, or if the insulation allows the magnet wire to touch the metal core, the motor would ground and fail.

The mechanical strength is very important for the insertion of the product and resistance to abrasion. All products also have different techniques that must be used in cutting or crafting in order for them to fit into the electrical device you are building or repairing. This is good to know as some products will increase your cost due to inflated manufacturing costs.

Another product used in insulating an electrical device is resin or varnish - this is not the varnish that protects the finish of the furniture in your home. However, this varnish protects in a similar way. These varnishes and resins are specifically matched to an appropriate insulation class and help protect, bond and insulate the magnet wire, flexible insulation and tape insulation system. The selection of this primary insulation component is very important as it is associated with the other insulation materials that are considered compatible in the insulation system.

Also, the electrical equipment will typically carry the insulation class rating in that system. Logically one would expect that if all Class H products are used in an electrical apparatus then the apparatus should have a Class rating of H; however, this is not always the case. In some cases there are instances where the individual insulation products used in the overall system can reduce and sometimes increase the class rating as they can behave together in a sealed pipe test.

Each device should be tested on a full UL and/or IEEE scheme to truly confirm that the device meets a specific classification; various UL systems are available from paint and flexible insulation manufacturers. Within this UL rating, a point of contention in the electric motor industry is whether the lead wire counts for the connections in the system. Currently, the lead wire is not considered part of the insulation in the motor. Since it is not part of the motor insulation, the lead wire can be classified in a lower temperature class than the insulation inside the motor and does not reduce the overall temperature class. As previously mentioned, this is and will continue to be a point of contention for many manufacturers and converters.

OTHER CONSIDERATIONS
Temperature class, voltage and mechanical strength decisions are the key characteristics that will help you select the best insulation for your setup, but there are other decisions that are more specific to the insulation needs of your application. These include but are not limited to dielectric properties, ambient air temperature, moisture absorption (humidity), physical weight, available size, corona resistance, and more.

Once you have reached this level, get in touch with a qualified molded case distributor and provide them with more details about your application. These experts are very good at identifying and selecting the best products for your application needs.