What are Electrical Connectors?

Electrical circuits are composed of a multitude of components, including wires and cables. Electrical connectors are used to join these to form a continuous path for electrical current to flow. Connectors have male-ends (plugs) and female-ends (jacks) which connect to each other forming either a permanent connection or, more often, a temporary connection that can be assembled and removed with special tools.

Electrical connectors drastically reduce the time, effort and manpower needed for manufacturing, assembling and installing electrical devices, their components as well as wiring.


Most connectors have two main parts – the housing, and terminals for making the connections:

  • Housing – The housing is the structure or case used to contain the terminals, ensure stability of the connections and protect the electrical contacts from short-circuiting and environmental hazards. Connector housings are normally made of molded plastic, but other insulating materials like ceramics are also used.
  • Terminals – Terminals are the pins in a connector which provide electrical conduction to make the connections secure. They are almost always composed of a metal, but some of them use other conductive materials (carbon, silicon, etc.).


For some applications, electrical connectors that possess different features might be required or preferred:

  • Keyed Connectors – These are designed to connect only when they are in the proper orientation. This prevents accidental damage to the pins and prevents users from inserting them in the wrong sockets.
  • Locked Connectors – A locking mechanism ensures the connectors are held in place, preventing connections from breaking accidentally, or from shifting when the connector is bumped or jolted.
  • Hermetically Sealed Connectors – Some applications require an electrical connection which might be submerged in water. These connectors are purpose built to be fully functioning under water and withstand pressure up to certain depths.
  • Water Resistant Connectors – While they usually can’t withstand being submerged, these connectors provide protection for the electrical connections against water damage from splashes or occasional dampness.
  • Moisture/Oil Resistant Connectors – These are designed to protect the electrical connections from damage caused by oil or moisture.
  • EMI or RFI Filtering – Additional features built into the housing top protect the connectors from electromagnetic interference (EMI) or radio frequency interference (RFI), which can affect circuits carrying electrical signals.
  • ESD Shielded Connectors – Electrostatic discharge can damage wiring and components. ESD shielded connectors provide additional protection against this.


To select the right electrical connectors that will get the job done and minimize risks, there are a few factors which should be considered, depending on the application, type of connectors and the strength of the electrical current the circuit will carry. These can be broken down into two classifications:

  • Performance Parameters
  • Performance parameters need to be selected based on the conditions in which the electrical connector is going to operate-

    • Current – The current rating describes the rate of electricity flow (current) a connector is designed to accommodate. This is measured in amperes (A or amps). The Current rating on a connector will usually be in the range of 1A to 50A, though smaller and larger ones are available for special applications.
    • Voltage – The voltage rating describes the range and type of voltage the connector is designed to carry. This is measured in volts (V) for the voltage and Alternating Current (AC) or Direct Current (DC). Typically, the ratings can be 50V, 125V, 250V, and 600V, but others are available too.
    • Operating Temperature – The operating temperature range describes the range, recommended temperature and minimum/maximum safe operating temperature for the electrical connector.
  • Physical Parameters
  • Physical parameters should be selected carefully, since they describe how the electrical connector is designed, the connections it can be used for and much more:

    • Contact Pitch – This is the distance the centers of adjacent pins or the terminals in a connector. It is usually measured in millimeters (mm). Larger contact pitches mean fewer connections or pins per area, which reduces electrical arcing and thereby, interference. However, it does increase the overall size of the connector.
    • Number of Contacts – Apart from the type of contact pitch, the number of contacts or individual conductive elements present in electrical connectors also vary.
    • Material – While the connector casings are usually made of plastic, the materials used for the connectors are usually a combination of metal and plastic for insulation, though just about any conductive material can be used. The properties of the materials affect the performance, like conductivity, strength, resilience and formability. Some commonly used ones include:

      • Brass – Zinc content can vary from 5-40%; cheapest metal to purchase by weight; springy; strong; high conductance, used in KK terminals
      • Phosphor Bronze – Good strength; tough; high conductibility and fatigue resistance; flexible and elastic, used in electrical contact springs
      • Beryllium Copper – Best alloy for spring terminals; cheaper than phosphor bronze, used for high-performance applications
      • High Copper Alloy – Strong modified copper; good electrical and thermal properties; retains its form at high temperatures, mainly used in automotive applications

      Types of Electrical Connectors

      There are many types of individual electrical connectors, which can be categorized by level, function, and type of termination:

      • Connector Level – Each of the connector types can be divided into one or many of these five categories, referred to as connector levels:

        • Wire-to-board or subassembly-to-subassembly
        • Box-to-box or input/output
        • IC chip or chip-to-package
        • IC package or package-to-board
        • PC board-to-board
      • Connector Function – Although a lot of connectors are application-specific, most of them can be classified based on their method of connection:

        • Terminal Block – In these connectors, multiple wires are individually connected to a single terminal point and enclosed in housing. There are many sizes, but the lack of circuit protection makes them more cumbersome in comparison with some others. The connections include printed circuit board (PCB) terminal blocks, pluggable terminal blocks, multiple terminal connectors (MTC), and barrier strips. These are used on PCBs and various other electrical devices.
        • Binding Post – These connect bare wires to posts and fasten them with screws or clamps. The other end can connect to terminals, pins, or plugs. Many posts can connect with banana plugs, pin connectors, and lug terminals. These are used for a variety of audio and electronic testing devices.
        • Plug and Socket – A female socket with one or more pins connects into a male socket or plug. This provides easy, allowing connections to be made without tools. A pinout diagram can be helpful for multi-pin connectors. The connection types include USB, network cable, HDMI, DVI, RCA, SCSI, board mount, audio, coaxial, cable, etc. Often used in most consumer electronics that handle video and audio, automotive applications, computing, and PCBs.
        • Rack and Panel – These connectors are usually used to connect stationary equipment with removable electronic parts, especially when space or reliability of the connection are important factors. Connection types include rack to panel, cable to cable, and cable to panel. They are often used in printers, modems, home stereo systems and telecommunications.
        • Blade – Blade connectors connect individual wires to blade receptacles with the use of flat conductive blades. Blades connectors are sometimes hard-fastened to connecting wires in some electronic devices, like speakers or thermostats. They are usually used for connecting wire and are suitable for just about every application that requires point to point connections.
        • Ring and Spade – Like blade connectors, they connect a single wire, except the connection is secures by sandwiching between a threaded post and a screw or bolt The shape allows for easy connections that can be removed when the lock is only partially opened. These are mostly used for connecting wire and are also suitable for just about any application that requires point to point connections.
      • Connector Termination – Some connectors can be classified on the basis of the method used to terminate or fasten the wire to the connector:
        • Insulation Displacement – Insulation displacement connectors (IDCs) connect insulated cable or wire without requiring any pre-stripping of the insulation. A sharp blade or a series of blades in the connector cut into the insulation when the wire or cable is inserted. While the elimination of the stripping process cuts down time, especially for manufacturers, the blades can severe the wire. This lowers the current handling capability. Additionally, non-production IDC tools are more expensive and less effective than crimping tools.
        • Crimping – Crimping creates a separable connection between connectors and wires. A stripped wire is inserted into a metal barrel or terminal and a crimping tool is used to compress a section over the wire. This is commonly used to terminate stranded wire for ring, blade and spade connectors. They are preferred for their safety, easy-of-use, cost-effectiveness and post-production reproducibility.

          • Barrel connections crimp cylindrical sections, usually into oval-like shapes and are widely used in consumer electronics
          • Open-barrel connections crimp a pre-crimp section, resulting in a U or V shape. These are easier to automate and generally stronger than the barrel-crimped connections
      • Soldering – Soldering involves melting filler metal (solder) over an electrical joint to create a fused connection between conductors or terminals. This provides a very smooth and robust if done correctly, using a solder that matches the metals being joined. These connections take a longer time and are more involved than crimping. In PCBs, electrical connections are made by soldering pins or wires onto the mounting locations. Components can also be mounted and soldered on the other side of the board using through-hole technology (THT).