# Connector Temperature Rise Test Methods and Key Points of Current Carrying Capacity Verification
The current carrying capacity of a connector is one of its core electrical parameters, directly related to the safety and reliability of connector use. When current passes through a connector, due to the existence of contact resistance and the resistance of the conductor itself, Joule heat is generated, causing the connector temperature to rise. If the temperature rise is too high, it will not only accelerate the aging of insulating materials and reduce mechanical performance, but may also cause safety hazards. Therefore, temperature rise testing is the core means of verifying the current carrying capacity of connectors, and also an important basis for product design and selection. This article introduces in detail the methods and standards of connector temperature rise testing, as well as the key points of current carrying capacity verification.
## 1. Generation and Impact of Connector Temperature Rise
### Causes of Temperature Rise
After current flows through the connector, the temperature rises, mainly generated by the following three heat sources:
**1. Conductor Resistance Heating**: The connector terminals and cables themselves have resistance, and Joule heat is generated when current passes through. This part of the heat is proportional to the resistance value and the square of the current (P = I²R). For high-current connectors, the heat generated by the conductor itself cannot be ignored.
**2. Contact Resistance Heating**: This is the main source of connector temperature rise. When two metal surfaces are in contact, the actual contact area is much smaller than the apparent area, and current is only conducted through a small number of contact points, forming a large contact resistance. The heat generated by contact resistance is the main contributor to connector temperature rise. Contact resistance consists of two parts: constriction resistance (concentration resistance) and film resistance (surface oxide film, contamination film).
**3. Other Loss Heating**: For high-frequency applications, there are also dielectric loss, eddy current loss, etc., but these can be ignored under DC and power frequency conditions.
The final temperature of the connector equals the ambient temperature plus the temperature rise (ΔT). When heat generation and heat dissipation reach equilibrium, the temperature tends to stabilize, and the temperature rise at this time is the stable temperature rise of the connector under that current.
### Hazards of Excessive Temperature Rise
Excessive connector temperature rise will bring various hazards:
**Accelerated Insulation Aging**: High temperature will accelerate the thermal aging of plastic insulating materials, reducing their mechanical strength and electrical performance, and shortening product service life. Empirical data shows that for every 10°C increase in temperature, the aging rate of organic materials approximately doubles.
**Reduced Contact Reliability**: High temperature will accelerate the oxidation and corrosion of contact surfaces, leading to increased contact resistance and further intensifying heat generation, forming a vicious cycle. In severe cases, it may lead to contact failure.
**Affected Mechanical Performance**: Temperature rise will reduce metal elasticity and decrease contact normal force, further increasing contact resistance. High temperature may also cause plastic housing softening and deformation, affecting assembly precision.
**Safety Hazards**: In extreme cases, excessive temperature rise may cause plastic melting, combustion, and even fire. Especially in unattended equipment, out-of-control temperature rise is a major safety hazard.
**Affecting Adjacent Components**: The high temperature of the connector will radiate and conduct heat to the surroundings, affecting the normal operation of nearby other components.
Therefore, the temperature rise of connectors must be controlled within allowable limits, which is the basic requirement for ensuring safe and reliable product operation.
## 2. Standards and Methods of Temperature Rise Testing
Connector temperature rise testing needs to be carried out according to relevant standards to ensure the accuracy and comparability of test results.
### Main Test Standards
**IEC 60512-5-1 / GB/T 5095.501**: Electromechanical components for electronic equipment (connectors) test procedures — Part 5-1: Current-carrying capacity tests — Test 5a: Temperature rise. This is the core industry standard for connector temperature rise testing, specifying the test methods, equipment requirements, and test procedures for temperature rise testing.
**IEC 60998 / GB 13140**: Connecting devices for low-voltage circuits for household and similar purposes — Temperature rise test methods, applicable to building electrical connectors.
**MIL-STD-1344 / EIA-364 Series**: US military standards and Electronic Industries Association standards, which include methods for testing connector current carrying capacity and temperature rise.
**UL 1977 / UL 2238**: Requirements for connector temperature rise and current carrying tests in US UL safety standards.
**Various Enterprise Standards**: Each OEM and connector manufacturer usually has more detailed enterprise test specifications.
### Test Methods and Equipment
**1. Test Sample Preparation**
– Test samples should be in finished state, including complete assembly of plastic housing, terminals, cables, etc.
– Cable length, cross-section, and material should meet specified requirements, as the heating of the cable itself will affect the test results.
– The number of samples is generally not less than 3 pairs (male and female mating state), and the worst value or average value is taken as the final result.
– Before testing, samples should be in a dry and clean state without mechanical damage.
**2. Test Environment**
– Testing should be conducted in a windless or very low wind speed environment to avoid air flow affecting heat dissipation and temperature measurement.
– Ambient temperature should be controlled within the specified range (usually 20°C~25°C) and remain stable during the test.
– Test samples should be kept at a sufficient distance from surrounding objects to avoid heat exchange effects.
**3. Power Supply and Current**
– Use DC or AC constant current power supply capable of providing stable test current.
– Current accuracy should meet standard requirements (generally within ±2%).
– The current introduction method should minimize the impact on the sample temperature field.
**4. Temperature Measurement**
– Common temperature measurement methods include thermocouples (Type T, Type K), infrared temperature measurement, thermistors, etc.
– The thermocouple method is the most commonly used method. Thermocouples are welded or fixed at the measured point, with high measurement accuracy.
– The selection of temperature measurement points is very critical. Usually, the position with the highest temperature is selected, such as the contact area, the thinnest part of the terminal, etc.
– Thermocouples need to be calibrated regularly to ensure measurement accuracy.
### Test Procedure
A typical temperature rise test procedure is as follows:
1. **Sample Installation and Wiring**: Mate the male and female connectors in place, lock according to the specified torque or method. Connect test cables and current leads.
2. **Install Thermocouples**: Install thermocouples at specified positions (usually terminals or housings in the middle of the connector) to ensure thermocouples are in close contact with the measured surface.
3. **Initial State Confirmation**: Record ambient temperature and sample initial temperature before energizing, confirming that both are basically consistent.
4. **Energize for Temperature Rise**: Pass the specified test current and start timing.
5. **Temperature Monitoring**: Record temperature data at regular intervals and plot the temperature rise curve.
6. **Stability Judgment**: When the temperature change rate is less than the specified value (e.g., no more than 1°C change within 15 minutes), it is considered that thermal equilibrium has been reached, and the temperature at this time is recorded.
7. **Power Off for Cooling**: After reaching stability, power off and observe the cooling process (required by some standards).
8. **Result Calculation**: Temperature rise = stable temperature – ambient temperature.
## 3. Key Points of Current Carrying Capacity Verification
Current carrying capacity (Current Rating) refers to the maximum current value that a connector can safely carry for a long time under specified conditions. Determining current carrying capacity is a systematic engineering task that requires comprehensive consideration of multiple factors.
### Method for Determining Current Carrying Capacity
The rated current of a connector is usually determined through temperature rise testing. The basic principle is: at a specified ambient temperature, when a connector is energized with a certain current and its temperature rise does not exceed the specified limit, that current is the current carrying capacity of the connector under those conditions.
Common temperature rise limit standards:
– **General Industrial Connectors**: Temperature rise usually does not exceed 30K (i.e., at an ambient temperature of 25°C, the maximum temperature does not exceed 55°C)
– **Automotive Connectors**: According to standards such as USCAR, the temperature rise limit is usually 30K~55K, depending on the application location
– **High-Voltage High-Current Connectors**: The temperature rise limit may be higher, but it must be ensured that the maximum operating temperature of the insulating material is not exceeded
– **Limited by Maximum Material Temperature**: A more scientific approach is to use the long-term operating temperature of the insulating material as the upper limit and back-calculate the allowable temperature rise
It should be noted that current carrying capacity is not a fixed value, but is closely related to factors such as ambient temperature, installation conditions, cable specifications, etc.
### Key Factors Affecting Current Carrying Capacity
**1. Terminal Material and Cross-Section**
– The larger the conductive cross-section of the terminal, the smaller the resistance and the stronger the current carrying capacity.
– The higher the conductivity of the material (e.g., pure copper > brass > phosphor bronze), the stronger the current carrying capacity at the same cross-section.
– The shape of the terminal and the current density distribution will also affect the heating situation.
**2. Contact Resistance**
– Contact resistance is the main source of connector heating. Reducing contact resistance can significantly improve current carrying capacity.
– Contact normal force, contact area, surface plating, cleanliness, etc. all affect contact resistance.
**3. Heat Dissipation Conditions**
– The heat dissipation capacity of the connector directly affects temperature rise. The better the heat dissipation, the lower the temperature rise at the same current and the stronger the current carrying capacity.
– Heat dissipation methods include conduction heat dissipation (through PCB, terminals, cables), convection heat dissipation (through air), and radiation heat dissipation.
– Connectors mounted on large-size PCBs have better heat dissipation and higher current carrying capacity; connectors in enclosed spaces have poor heat dissipation, and current carrying capacity needs to be derated.
**4. Ambient Temperature**
– The higher the ambient temperature, the smaller the allowable temperature rise margin and the lower the current carrying capacity.
– It is usually necessary to provide a temperature derating curve for current carrying capacity to guide users in selecting appropriate current values at different ambient temperatures.
**5. Multi-pin Effect**
– For multi-pin connectors, when adjacent pins are energized simultaneously, heat will叠加, causing the temperature of the middle pin to be higher.
– When multiple pins are energized simultaneously, the current carrying capacity of a single pin needs to be appropriately derated.
### Multi-Factor Comprehensive Verification
Complete current carrying capacity verification usually requires considering the following multiple dimensions:
**Normal Temperature Current Carrying Test**: Test at standard ambient temperature (25°C) to determine the basic current carrying capacity.
**High Temperature Current Carrying Test**: Test at the maximum working ambient temperature to verify whether temperature rise requirements are still met under high temperature conditions.
**Multi-pin Energization Test**: All pins or a specified number of pins are energized simultaneously to evaluate mutual thermal effects.
**Different Wire Diameter Test**: Test using cables of different cross-sections to evaluate the impact of cable heat dissipation.
**Long-Term Aging Verification**: Current carrying life test, evaluating changes in contact resistance and temperature rise after long-term energization to verify long-term reliability.
## 4. Common Problems and Precautions
In the process of temperature rise testing and current carrying capacity verification, there are some common problems that require special attention:
### Comparability of Test Results
Temperature rise data obtained under different test conditions vary greatly and cannot be directly compared. When citing or comparing temperature rise data, the following conditions must be clarified:
– Ambient temperature
– Current magnitude
– Cable specifications (cross-section, length, material)
– Temperature measurement point position
– Installation method (on PCB / free hanging / enclosed space)
– Number of simultaneously energized pins
Without any of these conditions, the data may be misleading.
### Relationship Between Contact Resistance and Temperature Rise
Contact resistance is the most critical factor affecting connector temperature rise. A connector with poor contact, even with a small current, may produce a very high temperature rise at the contact point. Therefore:
– Temperature rise testing can also indirectly reflect contact quality
– Excessive temperature rise differences between different samples of the same product may indicate problems with contact consistency
– Changes in temperature rise after mating cycle life or environmental testing can reflect the degradation of contact performance
### Derating Design
In practical applications, connectors should not operate at the rated current limit for a long time, and a certain derating margin should be left. General recommendations:
– Actual working current should not exceed 70%~80% of the rated current
– Further derating under high temperature environments
– For important circuits or applications with high reliability requirements, the derating range is larger
Reasonable derating can greatly improve the reliability and service life of connectors.
### Common Causes of Abnormal Heating
If abnormally high temperature is found during temperature rise testing, possible causes include:
– Poor contact with excessive contact resistance
– Terminal size is too small or material conductivity is insufficient
– Connector is not fully mated in place
– Plating quality problems or surface contamination
– Improper current lead connection introducing additional heating
– Incorrect temperature measurement method with measurement error
## 5. Testing and Application Recommendations
### Recommendations for Manufacturers
1. **Establish Complete Testing Capabilities**: Equip with professional temperature rise testing equipment and personnel to ensure the accuracy of product current carrying parameters.
2. **Provide Detailed Derating Curves**: Not just giving a single rated current value, but also providing derating curves under different temperatures and different installation conditions.
3. **Clarify Test Conditions in Specifications**: The test conditions for rated current should be clearly marked to avoid misuse by users.
4. **Focus on Long-Term Reliability**: Temperature rise testing should not only look at new samples, but also pay attention to changes after long-term use.
### Recommendations for Selection and Users
1. **Clarify Application Conditions**: Select connectors with appropriate current carrying capacity according to actual working current, ambient temperature, installation conditions, etc.
2. **Leave Derating Margin**: Do not let connectors operate at the rated current limit. It is recommended to use them with a 20%~30% derating.
3. **Pay Attention to Multi-pin Superposition Effect**: When multiple pins are energized simultaneously, the thermal superposition effect should be considered to confirm whether additional derating is required.
4. **Correct Use and Installation**: Ensure connectors are fully mated in place, cable cross-section meets current requirements, and avoid abnormal temperature rise due to improper installation.
5. **Regular Inspection and Maintenance**: For high-current connectors, regularly check for abnormalities such as heating, discoloration, and odor.
## Conclusion
Temperature rise testing is the core means of verifying connector current carrying capacity and is also an important guarantee for ensuring safe and reliable product operation. The temperature rise of connectors originates from the Joule heating effect of conductor resistance and contact resistance, among which contact resistance is the most important influencing factor. Current carrying capacity is not a fixed value, but is closely related to ambient temperature, installation conditions, cable specifications, number of energized pins, and other factors. Only under clear test conditions do current carrying parameters have practical significance.
RuiXin ShengYe has established a complete temperature rise testing and current carrying capacity verification system. The current carrying parameters in product specifications have all undergone strict testing and verification to ensure authenticity and reliability. For more information on connector temperature rise testing and current carrying capacity selection, please refer to the RuiXin ShengYe product series. We will provide you with professional technical support and high-quality connection solutions.
