Selecting Electrical Parameters of Electrical Connectors

Current describes the current (rate of flow of electricity) a Electrical connector is designed to carry, measured in amperes or amps (A). Current ratings on Electrical connectors usually range from 1 A to 50 A. Voltage describes the voltage rating of the Electrical connector, measured in volts (V). Typical ratings are 50 V, 125 V, 250 V, and 600 V.

Electrical connectors are electromechanical components that connect electrical lines. Therefore, the electrical parameters of the connector itself are the first consideration when selecting a connector.

Rated voltage of electrical connector
The rated voltage, also known as the working voltage, mainly depends on the insulating material used in the connecting machine and the distance between the contact pairs. Some components or devices may not be able to perform their proper functions when the voltage is lower than their rated voltage. The rated voltage of the connector should in fact be understood as the highest working voltage recommended by the manufacturer. In principle, the connector can work normally below the rated voltage. According to the withstand voltage (dielectric strength) index of the connector, the rated voltage is reasonably selected according to the use environment and safety level requirements. That is to say, the same withstand voltage index can use different maximum working voltages according to different use environments and safety requirements. This is also more in line with objective usage.

Rated current of electrical connector
The rated current is also called the working current. Like rated voltage, connectors generally work well below rated current. In the design process of the connector, the rated current requirement is met through the thermal design of the connector. Because when a current flows through the contact pair, due to the existence of conductor resistance and contact resistance, the contact pair will heat up. When its heat exceeds a certain limit, it will destroy the insulation of the connector and form a contact to soften the surface coating, causing failure. Therefore, to limit the rated current, in fact, it is necessary to limit the temperature rise inside the connector not to exceed the specified value of the design. The problem to be paid attention to when choosing is: for multi-core connectors, the rated current must be derated. This should be paid more attention to in the case of high current, for example, the φ3.5mm contact pair generally stipulates that its rated current is 50A. However, 5 ferrule electrical connectors need to be derated by 33%, and the rated current of each ferrule is only 38A. The more ferrules, the greater the derating range.

Contact Resistance of Electrical Connectors
Contact resistance refers to the resistance generated by two contact conductors at the contact part. There are two issues to be aware of when choosing:
First, the contact resistance index of the connector is actually a contact resistance, which includes contact resistance and contact resistance to conductors. Usually the conductor resistance is small, so the contact pair resistance is called contact resistance in many technical specifications.
Second, in the circuit connecting small signals, it is necessary to pay attention to the conditions under which the given contact resistance index is tested, because the contact surface will be accompanied by oxide layer, oil or other pollutants, and the surface of the two contacts will produce film resistance. When the thickness of the film layer increases, the resistance increases rapidly, making the film layer a poor conductor. However, the film layer will undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and high current. The contact pressure designed for some small-sized connectors is quite small, and the application occasions are only mA and mV levels. The film resistance is not easy to be broken down, which may affect the transmission of electrical signals. One of the contact resistance test methods in GB5095 “Basic Test Procedures and Measurement Methods for Electromechanical Components Used in Electrical Equipment” is “Contact Resistance – Millivolt Method”. In order to prevent the insulating film on the contact from being broken down, the DC or AC peak value of the open circuit electromotive force of the test circuit is not greater than 20mV, and the DC or AC test current is not greater than 100mA.

Shielding of electrical connectors
In modern electrical and electronic equipment, the density of components and their related functions are increasing, which puts strict limits on electromagnetic interference. Therefore, the connector is often closed with a metal shell to prevent internal electromagnetic energy from radiating or being interfered by an external electromagnetic field. At low frequencies, only magnetic materials can significantly shield the magnetic field. At this time, there are certain regulations on the electrical continuity of the metal shell, which is the shell contact resistance.