How are EV wiring harnesses different?

Wiring harnesses, sometimes called cable assemblies or cable looms, are used in every corner of the electronics industry, including consumer appliances, commercial devices, robotics and industrial systems, computers and servers, telecommunications equipment, medical systems, aerospace platforms, and of course, trucks and automobiles. However, the wiring harnesses used in electric vehicles (EVs) are among the most complex and demanding.

That can be somewhat surprising since the drive train components in an electric vehicle (EV) are more straightforward than those of an internal combustion engine (ICE) vehicle. Two factors contributing to the complexity of EV wiring harnesses are the use of high voltages in the drive train and the fact that all controls in an EV are communicated through the harness; there are no hydraulic or mechanical linkages common in ICE vehicles.

HV harnesses

The complexity of EV wiring harnesses starts with multiple high-voltage (HV) domains. HV domains include the motor harness, battery pack harness, and separate harnesses for fast charging and regenerative braking. Each of these HV harnesses must be designed to handle high currents efficiently.

In addition to efficiently carrying high currents and providing insulation for high voltages, these harnesses must handle high temperatures and high temperature rises. That requires large wire diameters, HV connectors, and cable protection.

Cable protection takes several forms. The cables, especially the motor drive cables, are shielded to control the generation of electromagnetic interference that can disrupt the operation of other vehicle systems.

To protect people who may contact the vehicle, Federal safety standards require that all EV makers use an orange outer covering for any HV cables outside of physical electrical protection barriers (Figure 1). Depending on the cable being protected, the covering can be a braided tube, textile or other tape, a corrugated tube, etc.

Not just HV

The wiring harnesses in the HV domains are also subject to high currents to deliver the high power levels needed by the EV drive train and fast charging for the batteries. Power levels of tens and even hundreds of kilowatts are common. Even with large-diameter cables, the IR losses can be significant and generate corresponding temperature rises.

The basic EV operating environment includes temperatures up to +125° C. Under some high load conditions, the surface temperature of the HV harness can reach +150° C.

Wire diameter and bending radius

One way to reduce the rise in temperature due to IR losses is to use a larger-diameter cable. Larger wires, with lower electrical resistance, generally have better thermal characteristics and can dissipate more heat, further reducing the temperature rise under high loads.

The tradeoff is that larger wires have a larger minimum bending radius, making it more difficult to form and route HV harnesses. If the recommended minimum bending radius is violated, the insulation layer, the shielding, or the conductor can be permanently damaged. Wire diameter also directly impacts HV connector selection.

HV connectors

HV connectors are an important element in HV wiring harness designs. HV connectors in EV wiring harnesses must combine high electrical performance, mechanical strength, and the ability to withstand high levels of shock and vibration and exposure to harsh environments. Some considerations include: