electric vehicle wire harness

Wire harnesses, sometimes also known as cable assemblies or cable harnesses, are used in every corner of the electronics industry, including consumer electronics, commercial equipment, robots and industrial systems, computers and servers, telecommunications equipment, medical systems, aerospace platforms, and of course, trucks and automobiles. However, the wire harnesses used in electric vehicles (EVs) are the most complex and demanding.

This might be a bit surprising since the drivetrain components in electric vehicles (EVs) are simpler than those in internal combustion engine (ICE) vehicles. Two factors that contribute to the complexity of EV wire harnesses are the use of high voltage in the drivetrain and the fact that all control devices in EVs communicate through the wire harness; there are no hydraulic or mechanical linkages commonly found in ICE vehicles.

HV Wire Harnesses

The complexity of electric vehicle wire harnesses begins with multiple high-voltage (HV) domains. HV domains include motor wire harnesses, battery pack wire harnesses, and separate wire harnesses for fast charging and regenerative braking. Each of these HV wire harnesses must be designed to handle large currents effectively.

In addition to effectively carrying large currents and providing insulation for high voltages, these wire harnesses must also handle high temperatures and temperature rises. This requires large wire diameters, high-voltage connectors, and cable protection.

Cable protection comes in various forms. Cables, especially motor drive cables, are shielded to control the generation of electromagnetic interference that could disrupt the operation of other vehicle systems.

To protect people who might come into contact with the vehicle, federal safety standards require all electric vehicle manufacturers to use orange housings on any HV cables outside the physical electrical protection barrier (Figure 1). Depending on the cable being protected, the covering can be a braided tube, textile or other tape, corrugated tube, etc.

Figure 1. High-voltage cables in electric vehicles are required to have an orange housing when outside the physical protection barrier.
(Image: Guchen Electronics)

It's Not Just About HV

The wire harnesses in the HV domain are also affected by large currents to provide the high power levels required for the EV drivetrain and battery fast charging. Power levels of tens or even hundreds of kilowatts are common. Even with large-diameter cables, IR losses can be significant and result in corresponding temperature rises. The basic EV operating environment includes temperatures up to +125°C. Under some high-load conditions, the surface temperature of HV wire harnesses can reach +150°C.

Wire Diameter and Bending Radius

One way to reduce the temperature rise caused by IR losses is to use larger-diameter cables. Larger wires, with lower resistance, usually have better thermal characteristics and can dissipate more heat, further reducing the temperature rise under high load. The trade-off is that larger wires have a larger minimum bending radius, which makes the formation and routing of HV wire harnesses more difficult. If the recommended minimum bending radius is exceeded, the insulation layer, shielding layer, or conductor may be permanently damaged. The wire diameter also directly affects the choice of HV connectors.

High-Voltage Connectors

HV connectors are important elements in the design of HV wire harnesses. The high-voltage connectors in electric vehicle wire harnesses must possess high electrical performance, mechanical strength, and the ability to withstand high levels of shock and vibration as well as exposure to harsh environments. Some considerations include: IP68 protection ratingInsulation resistance of at least 500MΩ at 1 kVdcHigh-voltage interlock mechanismConnection to the shielding of HV cables to ensure high EMI performance Chemically resistant housing materials.