Electrical Connectors Information
Electrical connectors are devices that join electrical circuits together. Most connectors are removable or temporary, but some can be permanent. Connectors make electronic products easier to assemble and manufacture. They also ease circuit repairs and allow flexibility in design and modification. They are used extensively on circuits for communications, computers, industrial machinery, and consumer electronics.
Most connectors are composed of two main parts: housing and terminals.
Housing is the case or structure used to hold the terminals, stabilize the connection, and protect the contacts from shorting and/or from various environmental hazards. Housing is normally made up of some type of molded plastic, but can be made out of any type of insulator material (e.g. ceramics).
Terminal pins in a connector provide the electrical conduction which makes the connection. They are nearly always made up of some type of metal, but any material that conducts electricity can be used (e.g. carbon or silicon).
There are a vast amount of individual electrical connector types which can be differentiated in a number of ways, namely by level, function, and termination.
Each connector type can fit into one (or more) of five categories, referred to as levels in industry. These were defined by various companies under the support of the National Electrical Distributors Association (NEDA).
- Wire-to-board or subassembly-to-subassembly level
- Box-to-box or input/output level
- IC chip or chip-to-package level.
- IC package or package-to-board level.
- PC board-to-board level.
Although many connectors are application specific, most can be classified based on its method of connection.
Terminal block - connects multiple wires individually to a single terminal point in an enclosed housing. They are available in many sizes, but they lack the circuit protection and connection simplicity of other connectors. Connection include PCB terminal blocks, multiple terminal connectors (MTC), pluggable terminal blocks, and barrier strips. Applications include printed circuit boards (PCBs) and various electrical devices.
Image Credit: ESTCO
Rack and panel - connects stationary equipment to removable electronic parts, used when space and reliability are important factors. Connection include cable to cable, rack to panel, and cable to panel. Applications include printers, modems, and telecommunications.
Plug and socket - connects plug (male end) consisting of one or more pins into a socket (female end). They provide easy connecting without tools. With multi-pin connectors, a pinout diagram is sometimes helpful. Connections include network cable, USB, HDMI, DVI, SCSI, board mount, coaxial, RCA, audio, cable, etc. Applications include consumer electronics, video, audio, automotive, computing, and PCBs.
Binding post - connects bare wire to a post using screws or clamps, where the other end may connect to pins, plugs, or terminals. Many posts accept banana plugs. Connections include banana plugs, pin connectors, wire, and lug terminals. Applications include audio and electronic test equipment.
Blade - connects a single wire to a blade receptacle using a flat conductive blade, where some blades are hard-fastened to electronic devices. They are mostly used to connect wire and are suitable for any application requiring point to point configuration.
Ring and spade - connects a single wire to a device by pushing a screw or bolt through a ring or spade shape. The spade shape allows connection and removal while partially screwed in. Like blade connectors, they are mostly used to connect wire and are suitable for any applications requiring point to point configuration.
Some connectors may be further characterized based on how the wire is terminated or fastened to the connector.
Crimping is used to create a separable connection between wires and connectors. It involves inserting a stripped wire into a metal section (barrel or terminal) and using a crimping tool to apply pressure and compress the section tightly around the wire. They are often used for terminating stranded wire. Ring, spade, and blade connectors use crimping to join a wire to the connector.
Crimping a wire connection. Image Credit: Cable Organizer
Crimped connections are often preferred for a number of reasons:
- Easy, fast, and cheap to make/reproduce connections in large-scale production.
- No dangerous processes involved in making the connection.
- Little mechanical strain in the connection.
Types of crimped connections include barrel and open-barrel.
Barrel connections involve the crimping of cylindrical sections which (depending on the tool) usually results in oval-like shape. These are widely used in common consumer applications.
Open-barrel connections involve the crimping of a pre-crimp section into a U or V shape. These connections are easier to automate and are generally stronger than barrel crimped connections, making them more common in industrial applications.
Insulation displacement connectors (IDCs) are used to connect insulated wire or cable to a device without pre-stripping the cable or wire. By incorporating a sharp blade or multiple blades in the connector, the insulation is cut as it is inserted.
Image Credit: Belit Elktronik
IDC connectors are great for manufacturers because it eliminates the stripping step, providing a simpler connecting process. However, over time the blade that cuts the insulation can cut wires within the connector, lowing current handling (which can cause connector burnout). Also, the strength of the connection is much lower than a crimped connection. Tools for non-production insulation displacement tend to cost more than effective crimping tools.
Solder connections involve melting a filler metal (solder) onto an electrical joint. The solder then solidifies, creating a fused connection between two metal items. Solder can provide a very smooth, robust, and reliable connection if done well and with the right type of solder (solder components should match the metals of the electronic components being joined). These connections are generally slower and more involved than crimped connections.
In PCB solder or solder pin termination, electrical connection is made by soldering wires or pins onto a printed circuit board. With solder cup terminations, soldering the connector onto the mounting location creates an electrical connection. Through hole technology (THT) mounts components on PCBs by inserting component leads in the board and then soldering the pins on the other side.
When selecting electrical connectors, there are a number of factors which may be important to consider, depending on the type of connector and its application.
Performance parameters describe the conditions at which an electrical connector is designed to operate.
- Current describes the current (rate of flow of electricity) a connector is designed to carry, measured in amperes or amps (A). Current ratings on connectors usually range from 1A to 50A.
- Voltage describes the voltage rating of the connector, measured in volts (V). Typical ratings are 50V, 125V, 250V, and 600V.
- Operating temperature describes the recommended, range, or minimum/maximum operating temperature(s) of the electrical connector.
Physical parameters describe how an electrical connector is physically designed.
Contact pitch - the distance (from center to center) between adjacent pins or terminals in a connector, typically measured in millimeters (mm). A larger contact pitch describes a lower connection density (less pins or connections per area). Pitch affects arcing, which occurs when two conductors are close (pitch is low), causing interference.
Number of contacts - the number of conductive elements that mate with a corresponding element to provide an electrical path.
Materials - the materials used to construct the connector. Connectors are typically made of metal and plastic, but can be constructed using just about any conductor and insulating material. Properties of conducting materials that are important for electrical contacts include conductivity, mechanical strength, formability, and resilience. Some common terminal metals are described in the table below:
Zinc content varies from 5-40%; cheapest metal by weight; good spring, strength, and electrical properties
Good strength, toughness, and conductibility; excellent fatigue resistance; superior elasticity
Electrical contact springs
Finest copper alloy for spring terminals; price significantly less than phosphor bronze
Applications demanding optimum performance
High copper alloy
High strength modified copper; good thermal and electrical properties; resists softening at high temperatures
Mainly automotive applications
Table Credit: Molex
Some applications may require electrical connectors to possess certain features.
Keyed connectors are designed to only connect at a specific orientation. This prevents the user from damaging pins or inserting them into the wrong sockets. Pins and casing are oriented so that the plug cannot be inserted incorrectly.
Image Credit: wikipedia | Dimensions Guide
Locked connectors provide a means to lock the connection in place, preventing the connection from being undone accidentally.
Hermetically sealed connectors are fully function underwater and can withstand water pressure up to a certain depth.
Water resistant connectors are designed to protect connections from water damage.
Moisture / oil resistant connectors are designed to protect connections from oil or moisture damage.
EMI or RFI filtering on connectors provides protection against electromagnetic interference (EMI) and/or radio frequency interference (RFI).
ESD shielded connectors provide protection against electrostatic damage (ESD) to an electrical connection.