What are the basics of electrical connectors?

What are Electrical Connectors?

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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.

Composition

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 the 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 that provides electrical conduction to make the connections secure. They are almost always composed of metal, but some of them use other conductive materials (carbon, silicon, etc.).
• Other Accessories - Mounting Ear&#;Shell&#;Board Lock&#;&#;

Features/Properties

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 that might be submerged in water. These connectors are purpose-built to be fully functioning underwater 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 to 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.

Specifications

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:

1. 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 between 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%, its metallic luster changes from orange-red to yellow as the zinc content increases; cheapest metal to purchase by weight; springy; strong; Brass is less conductive than pure copper. Under normal circumstances, it will not rust or corrode and can be used in connectors with lower strength requirements, usually 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 &#; Strongly 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:

1. 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

2. 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 the 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 to 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 wires and are also suitable for just about any application that requires point-to-point connections.

3. 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 downtime, 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).

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Device used to join electrical conductors

This rear panel of an integrated amplifier features a variety of electrical connectors Connectors on the back of a computer

Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between parts of an electrical circuit, or between different electrical circuits, thereby joining them into a larger circuit.[1]

The connection may be removable (as for portable equipment), require a tool for assembly and removal, or serve as a permanent electrical joint between two points.[2] An adapter can be used to join dissimilar connectors. Most electrical connectors have a gender &#; i.e. the male component, called a plug, connects to the female component, or socket.

Thousands of configurations of connectors are manufactured for power, data, and audiovisual applications.[3] Electrical connectors can be divided into four basic categories, differentiated by their function:[4]

In computing, electrical connectors are considered a physical interface and constitute part of the physical layer in the OSI model of networking.

Physical construction

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In addition to the classes mentioned above, connectors are characterised by their pinout, method of connection, materials, size, contact resistance, insulation, mechanical durability, ingress protection, lifetime (number of cycles), and ease of use.

It is usually desirable for a connector to be easy to identify visually, rapid to assemble, inexpensive, and require only simple tooling. In some cases an equipment manufacturer might choose a connector specifically because it is not compatible with those from other sources, allowing control of what may be connected. No single connector has all the ideal properties for every application; the proliferation of types is a result of the diverse yet specific requirements of manufacturers.[7]:&#;6&#;

Materials

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Electrical connectors essentially consist of two classes of materials: conductors and insulators. Properties important to conductor materials are contact resistance, conductivity, mechanical strength, formability, and resilience.[8] Insulators must have a high electrical resistance, withstand high temperatures, and be easy to manufacture for a precise fit

Electrodes in connectors are usually made of copper alloys, due to their good conductivity and malleability.[7]:&#;15&#; Alternatives include brass, phosphor bronze, and beryllium copper. The base electrode metal is often coated with another inert metal such as gold, nickel, or tin.[8] The use of a coating material with good conductivity, mechanical robustness and corrosion resistance helps to reduce the influence of passivating oxide layers and surface adsorbates, which limit metal-to-metal contact patches and contribute to contact resistance. For example, copper alloys have favorable mechanical properties for electrodes, but are hard to solder and prone to corrosion. Thus, copper pins are usually coated with gold to alleviate these pitfalls, especially for analog signals and high-reliability applications.[9][10]

Contact carriers that hold the parts of a connector together are usually made of plastic, due to its insulating properties. Housings or backshells can be made of molded plastic and metal.[7]:&#;15&#; Connector bodies for high-temperature use, such as thermocouples or associated with large incandescent lamps, may be made of fired ceramic material.

Failure modes

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The majority of connector failures result in intermittent connections or open contacts:[11][12]

Failure mode Relative probability Open circuit 61% Poor contact 23% Short circuit 16%

Connectors are purely passive components &#; that is, they do not enhance the function of a circuit &#; so connectors should affect the function of a circuit as little as possible. Insecure mounting of connectors (primarily chassis-mounted) can contribute significantly to the risk of failure, especially when subjected to extreme shock or vibration.[11] Other causes of failure are connectors inadequately rated for the applied current and voltage, connectors with inadequate ingress protection, and threaded backshells that are worn or damaged.

High temperatures can also cause failure in connectors, resulting in an "avalanche" of failures &#; ambient temperature increases, leading to a decrease in insulation resistance and increase in conductor resistance; this increase generates more heat, and the cycle repeats.[11]

Fretting (so-called dynamic corrosion) is a common failure mode in electrical connectors that have not been specifically designed to prevent it, especially in those that are frequently mated and de-mated.[13] Surface corrosion is a risk for many metal parts in connectors, and can cause contacts to form a thin surface layer that increases resistance, thus contributing to heat buildup and intermittent connections.[14] However, remating or reseating a connector can alleviate the issue of surface corrosion, since each cycle scrapes a microscopic layer off the surface of the contact(s), exposing a fresh, unoxidised surface.

Circular connectors

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Many connectors used for industrial and high-reliability applications are circular in cross section, with a cylindrical housing and circular contact interface geometries. This is in contrast to the rectangular design of some connectors, e.g. USB or blade connectors. They are commonly used for easier engagement and disengagement, tight environmental sealing, and rugged mechanical performance.[15] They are widely used in military, aerospace, industrial machinery, and rail, where MIL-DTL- and MIL-DTL- are commonly specified. Fields such as sound engineering and radio communication also use circular connectors, such as XLR and BNC. AC power plugs are also commonly circular, for example, Schuko plugs and IEC .

NMEA cabling using M12 connectors

The M12 connector, specified in IEC -2-101, is a circular electrical plug/receptacle pair with 12mm OD mating threads, used in NMEA , DeviceNet, IO-Link, some kinds of Industrial Ethernet, etc.[16][17]

A disadvantage of the circular design is its inefficient use of panel space when used in arrays, when compared to rectangular connectors.

Circular connectors commonly use backshells, which provide physical and electromagnetic protection, whilst sometimes also providing a method for locking the connector into a receptacle.[18] In some cases, this backshell provides a hermetic seal, or some degree of ingress protection, through the use of grommets, O-rings, or potting.[15]

Hybrid connectors

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Hybrid connectors allow the intermixing of many connector types, usually by way of a housing with inserts.[19] These housings may also allow intermixing of electrical and non-electrical interfaces, examples of the latter being pneumatic line connectors, and optical fiber connectors. Because hybrid connectors are modular in nature, they tend to simplify assembly, repair, and future modifications. They also allow the creation of composite cable assemblies that can reduce equipment installation time by reducing the number of individual cable and connector assemblies.

Mechanical features

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Pin sequence

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Some connectors are designed such that certain pins make contact before others when inserted, and break first on disconnection.[1] This is often used in power connectors to protect equipment, e.g. connecting safety ground first. It is also employed for digital signals, as a method to sequence connections properly in hot swapping.

Keying

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Examples of keyed connectors

XLR connector , showing the notch for alignment

A 4-pin Mini-DIN S-Video cable, with notches and a rectangular alignment pin

Many connectors are keyed with some mechanical component (sometimes called a keyway), which prevents mating in an incorrect orientation.[20] This can be used to prevent mechanical damage to connectors, from being jammed in at the wrong angle or into the wrong connector, or to prevent incompatible or dangerous electrical connections, such as plugging an audio cable into a power outlet.[1] Keying also prevents otherwise symmetrical connectors from being connected in the wrong orientation or polarity. Keying is particularly important for situations where there are many similar connectors, such as in signal electronics.[7]:&#;26&#; For instance, XLR connectors have a notch to ensure proper orientation, while Mini-DIN plugs have a plastic projection that fits into a corresponding hole in the socket (they also have a notched metal skirt to provide secondary keying).[21]

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Locking mechanisms

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Some connector housings are designed with locking mechanisms to prevent inadvertent disconnection or poor environmental sealing.[1] Locking mechanism designs include locking levers of various sorts, jackscrews, screw-in shells, push-pull connector, and toggle or bayonet systems. Some connectors, particularly those with large numbers of contacts, require high forces to connect and disconnect. Locking levers and jackscrews and screw-in shells for such connectors frequently serve both to retain the connector when connected and to provide the force needed for connection and disconnection. Depending on application requirements, housings with locking mechanisms may be tested under various environmental simulations that include physical shock and vibration, water spray, dust, etc. to ensure the integrity of the electrical connection and housing seals.

Backshells

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Backshells are a common accessory for industrial and high-reliability connectors, especially circular connectors.[18] Backshells typically protect the connector and/or cable from environmental or mechanical stress, or shield it from electromagnetic interference.[22] Many types of backshells are available for different purposes, including various sizes, shapes, materials, and levels of protection. Backshells usually lock onto the cable with a clamp or moulded boot, and may be threaded for attachment to a mating receptacle.[23] Backshells for military and aerospace use are regulated by SAE AS within the USA.[24]

To deliver ensured signal stability in extreme environments, traditional pin and socket design may become inadequate. Hyperboloid contacts are designed to withstand more extreme physical demands, such as vibration and shock.[20] They also require around 40% less insertion force[25] &#; as low as 0.3 newtons (1 ozf) per contact,[26] &#; which extends the lifespan, and in some cases offers an alternative to zero insertion force connectors.[27][25]

In a connector with hyperboloid contacts, each female contact has several equally spaced longitudinal wires twisted into a hyperbolic shape. These wires are highly resilient to strain, but still somewhat elastic, hence they essentially function as linear springs.[28][29] As the male pin is inserted, axial wires in the socket half are deflected, wrapping themselves around the pin to provide a number of contact points. The internal wires that form the hyperboloid structure are usually anchored at each end by bending the tip into a groove or notch in the housing.[30]

Whilst hyperboloid contacts may be the only option to make a reliable connection in some circumstances, they have the disadvantage of taking up greater volume in a connector, which can cause problems for high-density connectors.[25] They are also significantly more expensive than traditional pin and socket contacts, which has limited their uptake since their invention in the s by Wilhelm Harold Frederick.[31] In the s, Francois Bonhomme popularised hyperboloid contacts with his "Hypertac" connector, which was later acquired by Smiths Group. During the following decades, the connectors steadily gained popularity, and are still used for medical, industrial, military, aerospace, and rail applications (particularly trains in Europe).[28]

Pogo pins

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Pogo pin connectors

Pogo pin or spring loaded connectors are commonly used in consumer and industrial products, where mechanical resilience and ease of use are priorities.[32] The connector consists of a barrel, a spring, and a plunger. They are in applications such as the MagSafe connector where a quick disconnect is desired for safety. Because they rely on spring pressure, not friction, they can be more durable and less damaging than traditional pin and socket design, leading to their use in in-circuit testing.[33]

Crown spring connectors

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Typical crown spring plug and its female socket

Crown spring connectors are commonly used for higher current flows and industrial applications. They have a high number of contact points, which provides a more electrically reliable connection than traditional pin and socket connectors.[34]

Methods of connection

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Whilst technically inaccurate, electrical connectors can be viewed as a type of adapter to convert between two connection methods, which are permanently connected at one end and (usually) detachable at the other end.[7]:&#;40&#; By definition, each end of this "adapter" has a different connection method &#; e.g. the solder tabs on a male connector, and the male connector itself.[3] In this example, the solder tabs connected to the cable represent the permanent connection, whilst the male connector portion interfaces with a female socket forming a detachable connection.

There are many ways of applying a connector to a cable or device. Some of these methods can be accomplished without specialized tools. Other methods, while requiring a special tool, can assemble connectors much faster and more reliably, and make repairs easier.

The number of times a connector can connect and disconnect with its counterpart while meeting all its specifications is termed as mating cycles and is an indirect measure of connector lifespan. The material used for connector contact, plating type and thickness is a major factor that determines the mating cycles.[35]

Plug and socket connectors

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Plug and socket connectors are usually made up of a male plug (typically pin contacts) and a female socket (typically receptacle contacts). Often, but not always, sockets are permanently fixed to a device as in a chassis connector (see above), and plugs are attached to a cable.

Plugs generally have one or more pins or prongs that are inserted into openings in the mating socket. The connection between the mating metal parts must be sufficiently tight to make a good electrical connection and complete the circuit. An alternative type of plug and socket connection uses hyperboloid contacts, which makes a more reliable electrical connection. When working with multi-pin connectors, it is helpful to have a pinout diagram to identify the wire or circuit node connected to each pin.

Some connector styles may combine pin and socket connection types in a single unit, referred to as a hermaphroditic connector.[6]:&#;56&#; These connectors includes mating with both male and female aspects, involving complementary paired identical parts each containing both protrusions and indentations. These mating surfaces are mounted into identical fittings that freely mate with any other, without regard for gender (provided that the size and type match).

Sometimes both ends of a cable are terminated with the same gender of connector, as in many Ethernet patch cables. In other applications the two ends are terminated differently, either with male and female of the same connector (as in an extension cord), or with incompatible connectors, which is sometimes called an adapter cable.

Plugs and sockets are widely used in various connector systems including blade connectors, breadboards, XLR connectors, car power outlets, banana connectors, and connectors.

Jacks and plugs

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A jack is a connector that installs on the surface of a bulkhead or enclosure, and mates with its reciprocal, the plug.[36] According to the American Society of Mechanical Engineers,[37] the stationary (more fixed) connector of a pair is classified as a jack (denoted J), usually attached to a piece of equipment as in a chassis-mount or panel-mount connector. The movable (less fixed) connector is classified as a plug (denoted P),[37] designed to attach to a wire, cable or removable electrical assembly.[38] This convention is currently defined in ASME Y14.44-, which supersedes IEEE 200-, which in turn derives from the long-withdrawn MIL-STD-16 (from the s), highlighting the heritage of this connector naming convention.[36] IEEE 315- works alongside ASME Y14.44- to define jacks and plugs.

The term jack occurs in several related terms:

• The registered jack or modular jack in RJ11, RJ45 and other similar connectors used for telecommunication and computer networking
• The jack of manual switchboards, which is the socket fitting the original

  1

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  inch (6.35 mm) plug
• The

  1

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  4

  inch (6.35 mm) jack common to many electronic applications in various configurations, sometimes referred to as a headphone jack
• The RCA jack, also known as a phono jack, common to consumer audiovisual electronics
• The EIAJ jack for consumer appliances requiring a power supply of less than 18.0 volts

Crimp-on connectors

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A wire and connector being crimped together with a crimping tool

Crimped connectors are a type of solderless connection, using mechanical friction and uniform deformation to secure a connector to a pre-stripped wire (usually stranded).[1] Crimping is used in splice connectors, crimped multipin plugs and sockets, and crimped coaxial connectors. Crimping usually requires a specialised crimping tool, but the connectors are quick and easy to install and are a common alternative to solder connections or insulation displacement connectors. Effective crimp connections deform the metal of the connector past its yield point so that the compressed wire causes tension in the surrounding connector, and these forces counter each other to create a high degree of static friction. Due to the elastic element in crimped connections, they are highly resistant to vibration and thermal shock.[39]

Crimped contacts are permanent (i.e. the connectors and wire ends cannot be reused).[40]

Crimped plug-and-socket connectors can be classified as rear release or front release. This relates to the side of the connector where the pins are anchored:[20]

• Front release contacts are released from the front (contact side) of the connector, and removed from the rear. The removal tool engages with the front portion of the contact and pushes it through to the back of the connector.
• Rear release contacts are released and removed from the rear (wire side) of the connector. The removal tool releases the contacts from the rear and pulls the contact out of the retainer.

Soldered connectors

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Many plug and socket connectors are attached to a wire or cable by soldering conductors to electrodes on the back of the connector. Soldered joints in connectors are robust and reliable if executed correctly, but are usually slower to make than crimped connections.[1] When wires are to be soldered to the back of a connector, a backshell is often used to protect the connection and add strain relief. Metal solder buckets or solder cups are provided, which consist of a cylindrical cavity that an installer fills with solder before inserting the wire.[41]

When creating soldered connections, it is possible to melt the dielectric between pins or wires. This can cause problems because the thermal conductivity of metals causes heat to quickly distribute through the cable and connector, and when this heat melts plastic dielectric, it can cause short circuits or "flared" (conical) insulation.[40] Solder joints are also more prone to mechanical failure than crimped joints when subjected to vibration and compression.[42]

Insulation-displacement connectors

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Since stripping insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors which cut the insulation as the wire is inserted.[1] These generally take the form of a fork-shaped opening in the terminal, into which the insulated wire is pressed, which cut through the insulation to contact the conductor. To make these connections reliably on a production line, special tools accurately control the forces applied during assembly. On small scales, these tools tend to cost more than tools for crimped connections.

Insulation displacement connectors are usually used with small conductors for signal purposes and at low voltage. Power conductors carrying more than a few amperes are more reliably terminated with other means, though "hot tap" press-on connectors find some use in automotive applications for additions to existing wiring.

A common example is the multi-conductor flat ribbon cable used in computer disk drives; to terminate each of the many (approximately 40) wires individually would be slow and error-prone, but an insulation displacement connector can terminate all the wires in a single action. Another very common use is so-called punch-down blocks used for terminating unshielded twisted pair wiring.

Binding posts

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Binding posts are a single-wire connection method, where stripped wire is screwed or clamped to a metal electrode. Such connectors are frequently used in electronic test equipment and audio. Many binding posts also accept a banana plug.

Screw terminals

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Screw connections are frequently used for semi-permanent wiring and connections inside devices, due to their simple but reliable construction. The basic principle of all screw terminals involves the tip of a bolt clamping onto a stripped conductor. They can be used to join multiple conductors,[43] to connect wires to a printed circuit board, or to terminate a cable into a plug or socket.[7]:&#;50&#; The clamping screw may act in the longitudinal axis (parallel to the wire) or the transverse axis (perpendicular to the wire), or both. Some disadvantages are that connecting wires is more difficult than simply plugging in a cable, and screw terminals are generally not very well protected from contact with persons or foreign conducting materials.

Terminal blocks of various types

Terminal blocks (also called terminal boards or strips) provide a convenient means of connecting individual electrical wires without a splice or physically joining the ends. Since terminal blocks are readily available for a wide range of wire sizes and terminal quantity, they are one of the most flexible types of electrical connector available. One type of terminal block accepts wires that are prepared only by stripping a short length of insulation from the end. Another type, often called barrier strips, accepts wires that have ring or spade terminal lugs crimped onto the wires.

Printed circuit board (PCB) mounted screw terminals let individual wires connect to a PCB through leads soldered to the board.

Ring and spade connectors

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Ring style wire-end crimp connectors

The connectors in the top row of the image are known as ring terminals and spade terminals (sometimes called fork or split ring terminals). Electrical contact is made by the flat surface of the ring or spade, while mechanically they are attached by passing a screw or bolt through them. The spade terminal form factor facilitates connections since the screw or bolt can be left partially screwed in as the spade terminal is removed or attached. Their sizes can be determined by the gauge of the conducting wire, and the interior and exterior diameters.

In the case of insulated crimp connectors, the crimped area lies under an insulating sleeve through which the pressing force acts. During crimping, the extended end of this insulating sleeve is simultaneously pressed around the insulated area of the cable, creating strain relief. The insulating sleeve of insulated connectors has a color that indicates the wire's cross-section area. Colors are standardized according to DIN :

• Red for cross-section areas from 0.5 to 1 mm²
• Blue for cross-section areas from 1.5 to 2.5 mm²
• Yellow for cross-section areas over 4 to 6 mm²

Blade connectors

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Blade connectors (lower half of photo). Ring and spade terminals (upper half). Bullet terminals, male and female (right-center, with blue wires)

A blade connector is a type of single wire, plug-and-socket connection device using a flat conductive blade (plug) that is inserted into a receptacle. Wires are typically attached to male or female blade connector terminals by either crimping or soldering. Insulated and uninsulated varieties are available. In some cases the blade is an integral manufactured part of a component (such as a switch or a speaker unit), and the reciprocal connector terminal is pushed onto the device's connector terminal.

Other connection methods

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See also

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Connectors

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References

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General

• Foreman, Chris, "Sound System Design", Handbook for Sound Engineers, Third Edition, Glen M. Ballou, Ed., Elsevier Inc., , pp. &#;72.

Media related to Electrical connectors at Wikimedia Commons

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