Analysis of Automotive Waterproof Wiring Harnesses

Automotive wiring harnesses are equivalent to the nervous system of vehicles, connecting an increasing number of electrical devices and playing a crucial role in power transmission and signal communication. It directly affects the quality and performance of the vehicle. Therefore, in addition to meeting the basic performance requirements of the vehicle, the quality requirements for the wiring harness itself are also very high. Among them, waterproof performance is one of the key indicators for evaluating the quality of wire harnesses and plays a crucial role.

This article introduces some common measures to improve the waterproof performance of automotive wiring harnesses.

1. Division of Automotive Waterproof Zones

The vehicle can be divided into wet zones and dry zones. According to QC/T 29106-2014, Technical Conditions for Automotive Wire Harnesses, a dry zone refers to areas where the wire harness does not require special waterproof treatment, such as the cabin, passenger compartment, and trunk. This includes harnesses for the dashboard, roof, center console, and rear bumper. Wet zones are areas outside the dry zones where the harness requires special waterproof treatment, including the engine compartment and four doors. Examples include engine harnesses, front bumper harnesses, battery cables, and door harnesses.

1.1 Definition of Waterproof Ratings

The ISO 20653 standard, Road Vehicles - Degrees of Protection (IP Code) - Protection of Electrical Equipment Against Foreign Objects, Water, and Contact, introduces the concept of protection levels. These levels define the degree of protection against external elements such as water and are verified through standardized test methods. The specific definitions of waterproof levels are shown in Table 1.

1.2 Classification of Waterproof Ratings

Based on these definitions and the environmental stability of different zones, ISO 20653 provides examples of waterproof ratings for various automotive zones, as shown in Table 2. Additionally, QC/T 413-2002, Basic Technical Conditions for Automotive Electrical Equipment, specifies detailed requirements for waterproof levels in different zones:

Products under the hood or exposed externally should achieve IPX4, passing splash water tests.

Products in the cabin or trunk should meet IPX3, passing spray water tests.

Moreover, controllers, connectors, and related components should not be positioned within 100mm of the floor. If unavoidable, proper sealing measures must be implemented.

1.3 Definition of Wading Depth

During vehicle development, scenarios such as driving through flooded streets or low-lying areas require consideration of the vehicle's wading capability. This introduces the concept of the "wading line," representing the maximum depth the vehicle can safely traverse at a certain speed. For traditional fuel vehicles, no national standard specifies this; it is determined by manufacturers. Figure 1 shows the wading depth for a specific model.

For electric vehicles, the wading standards are stricter. For example, in Shanghai, the standard for new energy vehicles requires the vehicle to wade at:

15cm depth at ≥30 km/h for 10 minutes.

30cm depth at ≥5 km/h (forward and backward) for 10 minutes.

2. Waterproof Sealing Measures for Wire Harnesses

To meet the waterproof requirements in various zones, wire harnesses primarily require protection in wet zones and at dry-wet transition areas. The current waterproof measures can be divided into two categories: component selection and routing design.

2.1 Component Selection

Connectors

Waterproof connectors are commonly used in wet zones. These connectors ensure mechanical and electrical integrity under specific water pressure conditions. Features include:

Rubber Seals: Ensure sealing between connectors and plugs.

Waterproof Plugs and Blanking Plugs: Prevent water ingress through unused connector ports. These must match the wire gauge. (See Figure 2 & 3).

Heat Shrink Tubes

Areas like wire splices and ground terminals in wet zones require adhesive heat shrink tubes to prevent corrosion and ensure insulation. Tube selection depends on wire diameter and operating temperature (e.g., ≥125°C for engine compartments). Proper application involves control over:

Shrinking temperature

Positioning

Shrinkage ratio (See Figure 4).

Rubber Components

Rubber components are used in transition areas (e.g., firewalls, doors) to isolate wet and dry zones. The dimensions must ensure a tight fit between rubber components and sheet metal, considering radial tolerances.

Waterproof Clips

Clips at dry-wet transitions should avoid sheet metal perforations. If unavoidable, waterproof clips must be used, ensuring smooth surrounding surfaces for effective sealing. (See Figure 5).

ABS Wire Harnesses

ABS wiring must withstand movement, water splashes, and immersion. Sealing is achieved through rubber seals and over-molded components. Manufacturers often perform pressurized air tests for validation.

2.2 Routing Design

In addition to component selection, routing design impacts waterproof performance:

Component Orientation: Wet-zone connectors should face downward or be horizontal to prevent water pooling and ingress.

Routing Paths: Wire harnesses must ensure:

Wet-zone harnesses are positioned lower than dry-zone harnesses to prevent water transfer.

Unwrapped sections near transitions prevent capillary effects and use non-absorbent materials like PVC.

Additional drainage points enhance reliability (See Figure 6).

3. Waterproof Testing and Validation

3.1 Component Validation

Testing includes:

Temperature cycling, water spray, immersion, and pressure differential tests.

Rubber components undergo 0.3 MPa water spray tests to ensure no leakage.

Insulation resistance for wet-zone splices should exceed 100 MΩ after immersion tests. (See Figures 7 & 8).

3.2 Vehicle-Level Validation

Vehicle testing includes:

Waterproof Sealing Tests: Simulate real-world scenarios (e.g., spray chambers, car washes, high-pressure washing). Dry-zone harnesses are inspected post-test for damage.

Wading Tests: Evaluate performance under varying water depths and speeds.

Predictive Testing: Simulate accidental scenarios such as spills in cabins and trunks (See Figures 9 & 10).

4. Conclusion

This article analyzes the impact of component selection and routing design on wire harness waterproof performance. It outlines practical measures and validation tests to guide future improvements in automotive wire harness design.