Connectors are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the connector itself are the first consideration when selecting a connector. Correctly selecting and using electronic connectors is an important aspect of ensuring circuit reliability.

Electronic connectors (hereinafter referred to as connectors) can also be called plug sockets, and are widely used in various electrical circuits, serving to connect or disconnect circuits. Improving the reliability of connectors is primarily the responsibility of the manufacturers. However, due to the wide variety of connectors and their extensive applications, correctly selecting connectors is also an important aspect of enhancing connector reliability. Only through the joint efforts of both manufacturers and users can the full functionality of connectors be maximized.

Connectors can be classified in different ways. By frequency, there are high-frequency connectors and low-frequency connectors; by shape, there are circular connectors and rectangular connectors; by application, there are connectors for printed circuit boards, connectors for cabinets, connectors for audio equipment, power connectors, special-purpose connectors, and so on. The following mainly discusses the selection methods for low-frequency connectors (with a frequency below 3MHz).

Electrical parameter requirements

Connectors are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the connector itself are the first consideration when selecting a connector.

Rated voltage

Rated voltage, also known as working voltage, mainly depends on the insulating materials used in the connector and the spacing between contact pairs. Some components or devices may not function properly below their rated voltage. The rated voltage of a connector should be understood as the maximum working voltage recommended by the manufacturer. In principle, connectors can operate normally below the rated voltage. I tend to reasonably select the rated voltage based on the connector's withstand voltage (dielectric strength) indicators, according to the usage environment and safety level requirements. In other words, the same withstand voltage indicators can be used at different maximum working voltages based on different usage environments and safety requirements. This also aligns more closely with objective usage conditions.

Rated current

Rated current, also known as working current. Like the rated voltage, connectors generally operate normally below the rated current. During the design process of connectors, the thermal design is used to meet the rated current requirements because when current flows through the contact pairs, heat is generated due to conductor resistance and contact resistance. When the heat exceeds a certain limit, it can damage the insulation of the connector and soften the surface coating of the contact pairs, leading to failure. Therefore, limiting the rated current effectively limits the internal temperature rise of the connector to not exceed the specified design value. An important consideration when selecting is that for multi-core connectors, the rated current must be derated. This is particularly important in high current situations; for example, a φ3.5mm contact pair generally has a rated current of 50A, but when it is a 5-core connector, it must be derated by 33%, meaning each core's rated current is only 38A. The more cores there are, the greater the derating.

Contact resistance

Contact resistance refers to the resistance generated at the contact points of two conductive bodies. When selecting, two issues should be noted: first, the contact resistance indicator of the connector is actually the resistance of the contact pair, which includes contact resistance and conductor resistance of the contact pair. Typically, conductor resistance is relatively small, so the contact pair resistance is often referred to as contact resistance in many technical specifications. Second, in circuits connecting small signals, attention should be paid to the conditions under which the contact resistance indicator is tested, as the contact surfaces may have an oxide layer, oil, or other contaminants, leading to film layer resistance on the surfaces of the two contact pieces. As the thickness of the film layer increases, the resistance increases rapidly, making the film layer a poor conductor. However, under high contact pressure, the film layer can undergo mechanical breakdown, or under high voltage and high current, electrical breakdown can occur. For some small-sized connectors designed with relatively low contact pressure, used only in mA and mV levels, the film layer resistance may not be easily broken down, potentially affecting the transmission of electrical signals. In GB5095 "Basic Testing Procedures and Measurement Methods for Electromechanical Components in Equipment," one of the contact resistance testing methods, "Contact Resistance - Millivolt Method," specifies that to prevent the insulating film on the contact pieces from breaking down, the open-circuit electromotive force of the test circuit should not exceed 20mV, and the direct current or alternating current test current should not exceed 100mA. In fact, this is a testing method for low-level contact resistance, so for those with such requirements, connectors with low-level contact resistance indicators should be selected.