High-Performance Polyamide for Busbars Extrude first, then bend tightly: That's how to make compact 800-V busbars

How can busbars be routed in an electric car within extremely tight spaces without the insulation tearing? Specialty polyamides from Ems-Grivory adhere directly to copper and aluminum and can withstand tight bend radii down to the thickness of a single conductor, while still performing their function: They provide insulation at voltages up to 1,000 V and thermal loads up to 150 °C.

Shorter charging times are driving the development of electric powertrains and shifting system voltages from 400 V to 800 V and beyond. As electrical power increases, so do the operating temperatures in the current-carrying components. Solid copper or aluminum busbars are increasingly replacing traditional round cables in high-voltage electrical systems because they can carry high currents in a significantly smaller space. However, it is precisely this compact design that pushes conventional plastic jackets to their physical limits when exposed to heat and tight bending radii.

Electrical Insulation Under Thermal Load

Inside the vehicle, busbars connect key components such as the battery, inverter, DC-link systems, and power distribution units. In modern high-voltage architectures, typical conductor cross-sections range from 35 mm² to 120 mm². During fast charging, these busbars briefly heat up to around 130 °C, and during peak loads, they can even reach up to 150 °C.

With many standard plastics, however, the specific volume resistance drops dramatically as the temperature rises: Heat causes polymer chains and ions present in the material to become more mobile, so that the resistance often plummets by several orders of magnitude. In 800-V busbars and at temperatures up to 150 °C, an excessive drop in resistance leads to undesirable leakage currents, localized self-heating of the insulating layer, and, in extreme cases, electrical breakdown. This shortens the service life of the entire high-voltage system.

Tight bending radii require adhesion and ductility

In addition to thermal stress, the limited installation space within the battery pack and in the power electronics complicates the design. Bus bars rarely run in straight lines within the vehicle; instead, they wind tightly around battery modules and the edges of the housing. Manufacturers first coat the metal profiles with plastic using an extrusion process, cut them to length, and only then bend them into their final three-dimensional shape. In this process, the bending radii are often only one to two times the actual conductor thickness.

This forming process following extrusion subjects the polymer layer to uneven stress. On the outside of the bend, the plastic stretches significantly, but must neither tear nor fall below the required minimum wall thickness. At the same time, high compressive forces act on the inner side, which must not cause wrinkles or cause the layer to detach from the metal. If the layer detaches from the metal or develops wrinkles, the sheath loses its mechanical and electrical protective function.

Polyamides for voltages up to 1,000 V

For this application, the Swiss polymer specialist Ems-Grivory has developed adhesion-modified PA12-XE grades within its Grilamid portfolio that are patented for busbar applications up to 1,000 V. Even within the critical temperature range between 100 °C and 150 °C, the specific volume resistivity of these materials decreases significantly less than that of conventional insulating plastics. As a result, the electrical shielding remains stable even under high continuous and peak loads. At the same time, these polyamide grades achieve high adhesion directly to copper and aluminum surfaces.

Combined with high ductility, the insulating layer withstands subsequent bending in very tight spaces without damage. This allows designers to achieve thinner wall thicknesses and make more efficient use of the available installation space in electric vehicles. Thinner layer thicknesses, in turn, lower material consumption, reduce component weight, and drive down system costs. European and Chinese automakers are already using these specialty polyamides in series production for their current high-voltage architectures. (mg)