Connectors are electromechanical components used to link electrical circuits; therefore, their electrical parameters are the primary consideration during selection.
Rated Voltage
Also known as operating voltage, this parameter depends primarily on the insulating materials used and the spacing between contact pairs. Certain components or devices may fail to perform their intended functions if operated below their rated voltage. In practice, a connector's rated voltage should be understood as the maximum operating voltage recommended by the manufacturer. In principle, connectors function normally at voltages below the rated value. The author prefers to select the rated voltage based on the connector's withstand voltage (dielectric strength) rating, while also considering the operating environment and safety requirements. In other words, a connector with a specific withstand voltage rating can be used at different maximum operating voltages depending on the environment and safety standards-an approach that aligns well with real-world usage.
Rated Current
Also known as operating current. Like rated voltage, connectors generally function normally at currents below the rated value. During the design process, rated current requirements are met through thermal design; when current flows through the contact pairs, heat is generated due to conductor resistance and contact resistance. If the heat exceeds a certain limit, it can damage the insulation and cause the contact surface plating to soften, leading to failure. Therefore, limiting the rated current is essentially a matter of ensuring that the internal temperature rise does not exceed the design limit. A key consideration during selection is that for multi-pin connectors, the rated current must be derated. This is particularly important in high-current applications; for example, a contact pair with a 3.5 mm diameter typically has a rated current of 50 A, but in a 5-pin configuration, it must be derated by 33%, resulting in a rated current of only 38 A per pin. The greater the number of pins, the more significant the derating.
Contact Resistance
Contact resistance refers to the resistance generated at the interface where two conductive elements meet. Two points should be noted during selection: first, the specified contact resistance value actually represents the resistance of the contact pair, which encompasses both the interface contact resistance and the resistance of the conductors themselves. Since conductor resistance is usually low, the total resistance of the contact pair is often simply referred to as "contact resistance" in many technical specifications. Secondly, for circuits handling small signals, it is important to note the conditions under which the specified contact resistance was measured. Contact surfaces often accumulate oxide layers, oil, or other contaminants, creating "film resistance" between the mating surfaces. As the thickness of this film increases, resistance rises rapidly, effectively turning the film into a poor conductor. However, this film can undergo mechanical breakdown under high contact pressure or electrical breakdown under high voltage and high current. In some compact connector designs where contact pressure is very low and operating conditions involve only milliampere (mA) and millivolt (mV) levels, the film resistance may not break down, potentially interfering with electrical signal transmission. The "Contact Resistance-Millivolt Method"-one of the testing procedures outlined in the GB5095 standard (*Basic Testing Procedures and Measuring Methods for Electromechanical Components for Electronic Equipment*)-specifies that to prevent the breakdown of insulating films on contacts, the open-circuit electromotive force (DC or AC peak) of the test circuit must not exceed 20 mV, and the test current (DC or AC) must not exceed 100 mA.
Shielding
In modern electrical and electronic equipment, the increasing density of components and the growing interdependence of their functions necessitate strict controls on electromagnetic interference. Consequently, connectors are often enclosed in metal housings to prevent the radiation of internal electromagnetic energy or to block interference from external electromagnetic fields. At low frequencies, only magnetic materials provide effective shielding against magnetic fields. In such cases, specific requirements apply to the electrical continuity of the metal housing-specifically regarding the contact resistance of the housing itself.