A connector is an electromechanical component used to join electrical circuits. Consequently, the electrical parameters inherent to the connector itself are the primary considerations when selecting one.
Rated Voltage
Rated voltage-also known as operating voltage-is primarily determined by the insulating materials used in the connector and the spacing between the contact pairs. Certain components or devices may fail to perform their intended functions if operated at a voltage below their rated value. In practice, a connector's rated voltage should be interpreted as the maximum operating voltage recommended by the manufacturer. In principle, a connector will function normally at any voltage below its rated value. The author advocates for a rational selection of the rated voltage based on the connector's dielectric withstand voltage (or dielectric strength) specifications, while also taking into account the specific operating environment and safety requirements. In other words, a connector with a given dielectric withstand rating may be utilized at different maximum operating voltages depending on the specific operating environment and safety standards applicable to the application. This approach aligns more closely with actual field conditions.
Rated Current
Also known as operating current. As with rated voltage, a connector will generally function normally when operated at a current below its rated value. During the design phase, a connector's ability to meet rated current requirements is achieved through thermal design; this is necessary because when current flows through the contact pairs, the presence of conductor resistance and contact resistance inevitably generates heat within the contacts. If this heat generation exceeds a certain threshold, it can compromise the connector's insulation and cause the surface plating on the contact pairs to soften, ultimately leading to a failure. Therefore, establishing a rated current effectively serves to limit the internal temperature rise within the connector, ensuring it does not exceed the specified design limits. A critical point to observe during selection is that for multi-pin connectors, the rated current must be "derated" (reduced). This is a particularly important consideration in high-current applications; for instance, a contact pair with a diameter of 3.5 mm is typically rated for 50A. However, in a 5-pin connector configuration, this rating must be derated by 33%-meaning the effective rated current per pin drops to just 38A. Generally, the greater the number of pins, the larger the required derating margin.
Contact Resistance
Contact resistance refers to the electrical resistance generated at the interface where two conductive contacts meet. Two key points should be kept in mind when selecting a connector: First, the "contact resistance" specification listed for a connector actually represents the *contact pair resistance*-a composite value that includes both the true contact resistance (at the interface) and the inherent resistance of the contact conductors themselves. Since the resistance of the conductors is typically negligible compared to the interface resistance, the combined "contact pair resistance" is frequently referred to simply as "contact resistance" in many technical specifications. Secondly, in circuits involving small signals, it is crucial to pay close attention to the specific conditions under which the specified contact resistance values were tested. This is because contact surfaces can accumulate oxide layers, oil residues, or other contaminants, resulting in the formation of a resistive film between the two contact elements. As the thickness of this film increases, the resistance rises rapidly, causing the film to act as a poor conductor. However, such films can undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage or high current conditions. For certain compact connectors designed with relatively low contact pressures-typically utilized in applications involving signal levels in the millivolt (mV) and milliampere (mA) range-the resistive film may not be easily broken down, potentially compromising the transmission of electrical signals. One of the contact resistance measurement methods outlined in the standard GB 5095, *Basic Test Procedures and Measuring Methods for Electromechanical Components for Electronic Equipment*-specifically the "Contact Resistance: Millivolt Method"-stipulates that, to prevent the breakdown of insulating films on the contact elements, the open-circuit electromotive force (EMF) of the test circuit (whether DC or AC peak value) must not exceed 20 mV, and the test current (DC or AC) must not exceed 100 mA.
Shielding Effectiveness
In modern electrical and electronic equipment, the increasing density of components and the growing complexity of their inter-related functions impose strict requirements regarding electromagnetic interference (EMI). Consequently, connectors are frequently enclosed within metal housings to prevent the radiation of internal electromagnetic energy and to shield against interference from external electromagnetic fields. At low frequencies, only magnetic materials can provide significant shielding against magnetic fields. In such instances, specific requirements apply to the electrical continuity of the metal housing-specifically, the contact resistance of the housing itself.
