As the number of electronic components and sensors increases in modern vehicles, it has become vital to use automotive wire harness shielding to prevent noise.
Automotive wire harnesses usually consist of high and low-voltage cables, plus signal lines to transmit data to the ECU.
These cables can create EMI, causing faults like erroneous sensor operations.
So shielding is important, and let’s look at these shield types and their applications in vehicle wires.
Table of Contents
- What Are Shielded Automotive Wire Harnesses?
- Cable Shielding Types
- Automotive Wire Shielding Applications
- Measures To Take When Dealing With EMI in Automotive Wiring Harnesses
- Wrap Up
What Are Shielded Automotive Wire Harnesses?
Shielded automotive wire harnesses are cables wrapped in foils or other shields to protect them from electromagnetic radiation or electrical noise.
The typical shield materials are conducting polymer, metal braids (copper, aluminum, etc.), copper tape wrapping, and metal foil.
Foils stuck on polyester backings are more common because they are cheap and flexible.
But braided shields are better for protecting against low frequencies and are more flexible than foils. However, they are costlier.
Unshielded wire harnesses don’t have these protective cases but feature a helical wrapping with the wires twisted together.
This design helps prevent malfunctioning from EMI sources but does not safeguard the signals in the cables from EMI.
A flexible oxygen sensor cable
However, these cables have advantages like affordability, thin and lightweight design, flexibility, versatility, and ease of installation.
Cable Shielding Types
Cable shields usually fall into these categories.
Braided Shielding
A braided shield is a fabric-like weave made using interwoven copper, steel, aluminum, or tinned copper wires.
This naked-interwoven wire braid design is flexible and durable because it has high mechanical strength.
Braided shielding
This shield has a coverage ranging from 45-98% and is ideal for protection against low frequency.
But you can maximize its coverage by combining it with a foil. On the downside, these braided shielding wires are difficult to terminate.
Foil Shields (Metal-Coated Mylar)
Foil shields or mylar composite tape with aluminum are lightweight, easier/cheaper to produce, highly efficient, and can achieve 100% coverage.
Also, they are easy to terminate. All you need to do is connect them to a drain wire, which goes to the ground.
Spiral Shielding
This shielding applies to twisted pair wires. It involves shielding each pair using a foil, then wrapping all the twisted pairs in another foil with a drain wire running inside.
A foil-shielded cable with twisted wires
The design provides better flexibility than braided cables, broader coverage (90-99%), easier termination than braided cable shielding, and better control against RFI and EMI.
Automotive Wire Shielding Applications
These protected cables are typical in the following applications.
Audio Cables
Audio cables in the line of EMI or RFI can transmit distorted audio signals, resulting in unclear sound from the speakers.
Power Cables
Shielding in power cables is typical along medium and high voltage lines in electric vehicles to prevent corona discharge or a broad electrostatics field.
The shield safeguards these three components.
Corona discharge
High-Voltage Cable Shield
EV cables transmit high voltages from the charging port to the battery and from the battery to the motors.
These cables have four layers: a conductor, insulation, shield, and sheath.
The shield usually contains a tinned copper wire braid covered in aluminum foil.
Copper braids provide up to 95% coverage, where coverage refers to the shield’s ability to safeguard against EMI. The higher the percentage, the better.
High voltage cables in an electric vehicle
On the other hand, aluminum foil gives up to 100% coverage, but coverage in this case is only a physical property.
It doesn’t mean the shield reflects all EMI. Instead, it shows the foil can shield against low and high frequencies. Otherwise, you won’t need the braided copper.
Complex multi-core shielded cable constructions usually have an outer sheath consisting of a single or double layer of aluminum foil tape shield.
Besides protecting against a broader frequency spectrum, this tape keeps moisture out, enhances tensile strength, and improves bending resistance.
HV Cable-Connector Joint Shield
Shielding this joint requires a shielding ring, whose diameter must match that of the high-voltage wire harness.
The shielding ring requires crimping into position after installation. Alternatively, you can wrap the joint using bronze, copper, or tinned copper tape.
High Voltage Connector Shield
Shielding around the connector must provide maximum protection while withstanding extreme mechanical stress.
Also, it must be removable for servicing, maintenance, or repair.
High-voltage wire connectors
Coaxial Cables
Coaxial cables are typical in data and radio frequency transmissions, usually from antennas to routers and radios.
Signal transmission occurs via the central conductor, while the outer shield under the jacket keeps out the interference.
Coaxial cables with braided shields
Measures To Take When Dealing With EMI in Automotive Wiring Harnesses
Consider these safety measures when handling electrical interference in automobiles.
Ground Connection
Grounding overlap coupled with good grounding arrangement minimizes high-frequency impedance.
This grounding involves connecting the harness’s shielding layer to the vehicle’s body. Another benefit of grounding is it eliminates noise-producing ground loops.
A ground wire connected to the car’s body
Connector
Although braided shielding offers up to 95% coverage, while foils take it up to 100%, interference can occur along the connector.
So always pick a connector with a shielding capability that matches the cable shield.
Cable
Consider the interference levels before picking the most suitable electrical cable.
For instance, if the wire will pass near high EMI sources like ignition systems, pick one with braids and foils.
Increase the Wiring Filter
Long-wiring harnesses have higher chances of experiencing conduction and radiation interference.
So if you can’t do without them, increase the number of wiring harness filters, such as magnetic (ferrite) rings, along the line.
A ferrite ring filter to protect against EMI
We recommend using short harnesses with a minimal ring road area and low impedance to reduce the interference surface area.
Plan the Harness Installation
Planning the harness installation during the design process enables you to separate low and high-power circuits, which minimizes radiation and induction interference.
Try to position the low-power circuits near the signal source and the high-power circuits near the load. And try to increase the distance from the source of interference to the wires.
Wrap Up
Although automotive wire harness shielding is expensive, it is necessary for some parts of the vehicle to maintain signal integrity.
These shields come in various types, each with its strengths and weaknesses. And you can combine them for better EMI protection.
That’s it for this article. Get in touch if you need help picking the most suitable cable for your project. Cheers!
