With the widespread adoption of 800V high-voltage automotive platforms, large-scale deployment of high-power liquid-cooled ultra-fast charging, and continuous improvements in power density for AI computing servers, the competition in high-voltage connectors has moved beyond just terminal current-carrying capacity, temperature rise control, and liquid cooling. CTI (Comparative Tracking Index), a key parameter for insulating materials, has now emerged from behind-the-scenes material data sheets to become a mandatory threshold in product design and material selection.
To put it simply: CTI stands for Comparative Tracking Index, which essentially measures an insulating plastic housing’s ability to resist surface leakage tracking and carbonization that could lead to short circuits.
When moisture, dust, or salt-laden particles accumulate on a connector’s surface, the high-voltage electric field can cause weak leakage currents through these contaminants. The resulting heat continuously burns the material, forming a continuous conductive carbon path on the insulation surface—eventually leading to insulation failure, localized ablation, or even fire.
The higher the CTI value, the more resistant the material is to forming conductive carbon paths under wet or dirty conditions, offering greater safety redundancy at high voltage. The industry standard for premium high-voltage materials is CTI ≥ 600V (IEC Material Group I, UL PLC 0 – the highest rating). With the shift to 800V systems, the focus is no longer solely on terminal current capacity, thermal management, and liquid cooling technology. Instead, a previously overlooked metric – CTI – has now come to the forefront.
01
Why is CTI Being Brought to the Forefront with the 800V Upgrade?
CTI, or Comparative Tracking Index, measures the relative ability of solid insulating materials to resist surface leakage tracking under specified wet contamination conditions.
It should be noted that CTI is not a rated voltage or dielectric withstand indicator for connectors. According to IEC 60112, the maximum voltage applied in CTI testing is 600V AC, and the results are primarily used for material comparison and insulation coordination. They should not be directly interpreted as “a CTI 600 material can sustain 600V or 800V operating voltage over long periods.”
According to IEC’s material classification system, CTI ≥ 600 falls into Material Group I; in UL’s PLC classification system, this corresponds to PLC 0. These two classification methods are often confused within the industry, but they do not refer to the same standard.
With the upgrade from 400V to 800V, the system operating voltage has increased, imposing higher demands on connectors regarding creepage distance, electrical clearance, solid insulation, and transient overvoltage resistance.
Meanwhile, high-voltage components across vehicles continue to evolve toward miniaturization and integration. Connector manufacturers must fit higher voltage conductors into limited spaces while still meeting requirements for waterproofing, dustproofing, temperature resistance, vibration resistance, and long-term aging – making insulation safety design increasingly challenging.
Under identical working voltage, pollution degree, and structural conditions, using materials with a higher CTI rating helps reduce the risk of conductive tracking on insulating surfaces and provides greater flexibility in optimizing creepage distances.
Material suppliers and connector manufacturers have already introduced CTI 600 materials and products designed for high-voltage applications. For example, certain high-voltage connectors achieve 1000V-level performance by combining high-CTI materials with optimized creepage and electrical clearance designs. High CTI, hydrolysis resistance, halogen-free flame retardancy, and color stability are gradually becoming essential material requirements for high-voltage connectors in new-energy vehicles.
Shan Xiaohui, General Manager of Guangzhou Yiwai Technology Co., Ltd., stated that many high-voltage connectors are already designed structurally to accommodate 1000V or higher rated voltages during early development stages. Therefore, upgrading from 400V to 800V vehicles does not necessarily mean existing high-voltage connector product lines will be entirely phased out.
Based on publicly available product information, numerous 1000V-level high-voltage connection systems already exist in the industry. Some high-voltage connectors from Yiwai Technology are rated up to 1000V DC, and international connector companies such as TE have also launched products designed for 1000V applications.
Thus, the pressure brought by the 800V upgrade does not solely manifest in changes to product form factors or production line reconfiguration. For some companies, the more immediate challenge lies in the synchronized advancement of insulation material systems, flame-retardant systems, and long-term reliability validation.
02
CTI 600 Is Not A Universal “Safety Talisman” for High-Voltage Applications.
With the widespread adoption of 800V platforms, some industry perspectives regard CTI 600 as a unified threshold for high-voltage connectors. However, in practical engineering, there is no one-size-fits-all solution for high-voltage connections across all vehicle models and locations. Connectors vary significantly among different automakers, vehicle types, and even different positions within the same model – differing in operating voltage, contamination environment, sealing ratings, temperature, and transient overvoltage conditions.
Insulation coordination specified by IEC 60664-1 does not rely solely on CTI; instead, it requires separate evaluations of electrical clearance, creepage distance, and solid insulation, while comprehensively considering factors such as operating voltage, overvoltage, pollution degree, material group, and altitude.
Among these, CTI primarily influences the design of creepage distance.
A higher CTI means that the material is less likely to form conductive paths along its surface under contaminated or humid conditions. Under the same operating voltage and pollution level, high-CTI materials can help optimize creepage distance.
However, this does not mean that using CTI 600 materials automatically allows reducing electrical clearance or arbitrarily thinning insulation wall thickness. Electrical clearance is mainly affected by operating voltage, transient overvoltage, air medium, and altitude, while insulation wall thickness must also meet requirements for dielectric strength, mechanical strength, thermal aging, injection molding, and vibration impact.
In other words, CTI addresses an important aspect of high-voltage insulation but certainly not all aspects.
Differentiated material selection based on specific application locations is becoming a key approach for connector manufacturers to balance safety and cost.
In areas with high voltage, high temperature, or elevated contamination risk – such as battery packs, electric drive units, PDUs, charging interfaces, and chassis proximity – manufacturers typically prioritize high-CTI materials, combined with sufficient creepage distance, electrical clearance, sealing structures, and insulation isolation designs.
For components located inside enclosed compartments with relatively stable environments, appropriate material grades can be selected according to OEM specifications and product validation results, avoiding blind pursuit of single performance indicators that could lead to over-engineering.
Some products also employ structural solutions such as layered insulation, insulating ribs, barriers, or extended surface paths to optimize material usage while ensuring safety.
Therefore, the logic behind material selection for high-voltage connectors should not be “the higher the CTI, the better,” but rather a precise match between material performance and actual operating conditions.
03
More Challenging than Rising Material Costs is the Vehicle-Level Validation Cycle.
High CTI materials typically need to balance flame retardancy, heat resistance, hydrolytic stability, mechanical strength, color stability, and injection molding processability.
This means that upgrading materials is not simply a matter of switching one resin or increasing the CTI value by a few points. Changes in flame retardants, glass fibers, pigments, or thermal stabilizers can all affect tracking resistance, warpage, strength, and long-term reliability.
Especially under high-voltage direct current (HVDC) conditions, ionic impurities, halogen content, and leachable substances under high temperature and humidity may pose risks such as contact corrosion and degradation of insulation performance.
Currently, international material suppliers offering materials for high-voltage connectors typically emphasize multiple properties simultaneously – such as CTI 600, halogen-free flame retardancy, hydrolytic resistance, thermal aging stability, low ionic migration, and long-term color stability in orange. This indicates that material selection for high-voltage connectors has shifted from competition based on single performance metrics to a comprehensive evaluation of entire material systems.
Shan Xiaohui noted that in certain high-end high-voltage connector projects, international brands still hold significant advantages – not only because their CTI values are higher, but more importantly because their products have undergone extensive mass production validation, resulting in greater maturity in batch consistency, processing windows, and long-term aging data.
Domestic high-CTI materials have recently accelerated sample testing and project integration, but achieving large-scale substitution still requires overcoming hurdles related to batch-to-batch consistency, long-term reliability, and full vehicle validation cycles.
Therefore, assessing whether domestic materials are ready to replace imported ones cannot rely solely on initial CTI values measured in laboratories. Key factors to evaluate include:
Whether CTI performance remains stable after exposure to high temperature, high humidity, and thermal cycling;
- Consistency across different production batches;
- Ease of warping, leaching, or surface defects during injection molding;
- The ability to simultaneously meet requirements for flame retardancy, mechanical strength, and hydrolytic stability;
- And availability of sufficient long-term validation data at both the vehicle and component levels.
These represent the most difficult barriers for domestic high-voltage materials to overcome. At the same time, material upgrades bring new cost pressures.
Procurement and validation costs for high-CTI, low-halogen, or halogen-free flame-retardant materials are generally higher than those for conventional engineering plastics. Meanwhile, price competition in new energy vehicles continues to pressure the supply chain downstream.
On one hand, safety standards for high voltage continue to rise; on the other, automakers keep demanding cost reductions. As a result, high-voltage connector manufacturers face dual pressures: increased costs due to safety improvements and compressed margins from end-user pricing.
According to Shan Xiaohui, in some current projects, the cost of material upgrades is still largely absorbed internally by connector manufacturers. Leading companies typically avoid compromising key material specifications to gain pricing advantages instead focusing on cost reduction through structural optimization, improved material utilization, mold enhancements, and automation.
The ability to control overall costs without sacrificing safety is now becoming a critical competitive advantage for high-voltage connector manufacturers.
04
The Next Competitive Frontier Is No Longer about Endlessly Increasing CTI Values.
For connection applications rated at 1000V and higher, simply continuing to raise CTI figures is no longer a viable path.
IEC 60112 sets the upper limit for standard test voltage at 600V. The standard explicitly warns that CTI test results should not be used as the sole basis for determining safe creepage distances in equipment; designers must also conduct comprehensive evaluations considering overvoltage, pollution degree, and insulation structure.
This means that competition among connectors for high-voltage platforms will shift from focusing on “single material parameters” to system-level insulation coordination.
Future high-voltage connectors require simultaneous optimization of multiple aspects: material classification and long-term aging performance, creepage distance and electrical clearance, insulation ribs and barrier structures, sealing and drainage design, contamination control, terminal temperature rise, thermal management, and injection molding process consistency.
Li Yiping, from the Shenzhen Connector Industry Association, also believes that insulation safety for high-voltage connectors cannot rely solely on single material parameters. Instead, it should be achieved through integrated material and structural design to deliver complete system solutions.
High-CTI materials can enable more compact designs, but whether this material advantage translates into actual product superiority depends ultimately on a company’s simulation capabilities, structural design expertise, mold manufacturing processes, and validation systems.
For connector manufacturers, the real barrier today is no longer whether they can source CTI 600 materials, but rather whether they can understand the limitations of these materials and transform them into reliable, mass-producible, and cost-controllable high-voltage connection solutions.
Conclusion
The 800V high-voltage platform is pushing the competition in the new energy vehicle industry further down to the connector material level, beyond power semiconductors, batteries, and charging systems.
CTI has thus become a key indicator in selecting materials for high-voltage connectors, but it is neither the rated voltage of the connector nor the sole solution for high-voltage safety.
What truly determines the reliability of high-voltage connectors is an integrated insulation coordination system composed of materials, creepage distance, electrical clearance, solid insulation, sealing, thermal management, and manufacturing processes.
In this round of upgrades, connector manufacturers must address not just “whether to use CTI 600 materials,” but how to rebalance higher voltage, smaller size, and lower cost.
As ultra-fast charging technology continues to evolve, the next major challenge for high-voltage connectors will shift from mere material parameter competition to a comprehensive contest involving materials, structure, manufacturing processes, and validation capabilities.