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This rear panel of an audio power amplifier features a variety of electrical connectors
Connectors on the back of a 2018 computer
Schematic symbols for male and female connectors (see Gender of connectors and fasteners)

An electrical connector is an electromechanical device used to join electrical terminations and create an electrical circuit.[1] Most electrical connectors have a gender – i.e. the male component, called a plug, connects to the female component, or socket. 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.

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 constructionEdit

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

MaterialsEdit

Electrical connectors essentially consist of two classes of materials: conductors and insulators. Properties important to conductor materials are 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] This increases the electrical conductivity and durability. 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 which hold the parts of a connector together are usually made of plastic due to its insulating properties, and housings or backshells can be made of molded plastic or metal.[7]:15

Failure modesEdit

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 which 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 which increases their 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 connectorsEdit

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-5015 and MIL-DTL-38999 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 60309.

 
NMEA 2000 cabling using M12 connectors

The M12 connector, specified in IEC 61076-2-101, is a circular electrical plug/receptacle pair with 12mm OD mating threads, used in NMEA 2000, 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 connectorsEdit

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 featuresEdit

Pin sequenceEdit

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.

KeyingEdit

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 except with a correctly oriented matching connector.[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 which fits into a corresponding hole in the socket (they also have a notched metal skirt to provide secondary keying).[21]

Locking mechanismsEdit

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, screw locking, and toggle or bayonet systems. 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.

BackshellsEdit

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 AS85049.[24]

Hyperboloid contactsEdit

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 which 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 1920s by Wilhelm Harold Frederick.[31] In the 1950s, 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 pinsEdit

 
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 used for safety in applications such as the MagSafe connector, and can be less damaging than traditional pin and socket design, leading to their use in in-circuit testing.[33]

Crown spring connectorsEdit

 
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 results in a more electrically reliable connection than traditional pin and socket connectors.[34]

Methods of connectionEdit

Plug and socket connectors
Male MIL-DTL-5015 plug
Male serial port connector
Mating surfaces of a hermaphroditic connector

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 phone connector, and the male phone 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.

Plug and socket connectorsEdit

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 which can freely mate with any other, without regard for gender (provided that the size and type are already matched).

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 phone connectors.

Jacks and plugsEdit

A jack is a connector that is designed to be fixed on the surface of a bulkhead or enclosure, and mates with its reciprocal, the plug.[35] According to the American Society of Mechanical Engineers,[36] 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),[36] designed to attach to a wire, cable or removable electrical assembly.[37] This convention is currently defined in ASME Y14.44-2008 which supersedes IEEE 200-1975, which in turn was derived from the long-withdrawn MIL-STD-16 (from the 1950s), highlighting the heritage of this connector naming convention.[35] IEEE 315-1975 works alongside ASME Y14.44-2008 to define jacks and plugs.

The term jack occurs in several related terms:

Crimp-on connectorsEdit

 
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.[38]

Crimped contacts are permanent (i.e. the connectors and wire ends cannot be reused).[39]

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 connectorsEdit

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 which an installer fills with solder before inserting the wire.[40]

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.[39] Solder joints are also more prone to mechanical failure than crimped joints when subjected to vibration and compression.[41]

Insulation-displacement connectorsEdit

Since stripping the insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors so that the insulation is cut 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 and which cut through the insulation to contact the conductor within. To make these connections reliably on a production line, special tools are used which 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 on a bi-amplified loudspeaker

Binding postsEdit

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 will also accept a banana plug.

Screw terminalsEdit

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,[42] 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 allow individual wires to be connected to a PCB through leads soldered to the board.

Ring and spade connectorsEdit

 
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.

Blade connectorsEdit

 
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 using a flat conductive blade which is inserted into a receptacle. Wires may be attached to male or female blade connectors 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 is pushed onto the device's connector.

Common types of blade connectors are the Faston connectors and Lucar connectors. While Faston is a trademark of TE Connectivity (formerly Tyco Electronics), it has come into common usage. Faston connectors come in male and female types. They have been commonly used since the 1970s.

Other connection methodsEdit

See alsoEdit

ReferencesEdit

  1. ^ a b c d e f g "Electrical Connectors Information". Engineering360. IEEE GlobalSpec. Retrieved 30 June 2019.
  2. ^ Mroczkowski, Robert S. (1998). "Ch 1". Electrical Connector Handbook: Theory and Applications. McGraw Hill. ISBN 0-07-041401-7.
  3. ^ a b Elliott, Brian S. (2007). "Chapter 9: Connectors". Electromechanical Devices & Components (2nd ed.). McGraw-Hill Professional. ISBN 0-07-147752-7.
  4. ^ SFUptownMaker. "Connector Basics". SparkFun. Retrieved 30 June 2019.
  5. ^ David, Larry (17 March 2012). "Engineering Definitions - 'Com' to 'Con'". Electronic Engineering Dictionary Terms. Connector. Retrieved 30 June 2019.
  6. ^ a b Horowitz, Paul; Hill, Winfield (1989). The Art of Electronics (2nd ed.). Cambridge University Press. ISBN 0-521-37095-7.
  7. ^ a b c d e f Connectors - Technologies and Trends (PDF). ZVEI - German Electrical and Electronic Manufacturers’ Association. August 2016.
  8. ^ a b "Molex Connectors Explained, as used in Pinball". Marvin's Marvelous Mechanical Museum. 4 March 2005. Retrieved 1 July 2019.
  9. ^ Endres, Herbert. "Gold or Tin versus Gold and Tin?". Molex. Retrieved 1 July 2019.
  10. ^ AMP Incorporated (29 July 1996). "Golden Rules: Guidelines For The Use Of Gold On Connector Contacts" (PDF). Tyco Electronic Corporation. Archived from the original (PDF) on 29 March 2018. Retrieved 1 July 2019. Gold is generally specified as a contact coating for low level signal voltage and current applications, and where high reliability is a major consideration Cite journal requires |journal= (help)
  11. ^ a b c "Connectors: Failure Mechanisms and Anomalies" (PDF). Naval Sea Systems Command. Retrieved 1 July 2019.
  12. ^ Normalized failure mode distributions were originally compiled from a combination of: MIL-HDBK-978, “NASA Parts Application Handbook”, 1991; MIL-HDBK-338, “Electronic Reliability Design Handbook”, 1994; “Reliability Toolkit: Commercial Practices Edition", Reliability Analysis Center (RAC), 1998; and “Failure Mode, Effects, and Criticality Analysis (FMECA)”, RAC, 1993.
  13. ^ "Ribbon Cable Interconnect Solutions" (PDF). TE Connectivity. April 2012. p. 30. Retrieved 1 July 2019. By its design the traditional failure mode in tin plated connections, fretting corrosion, is prevented.
  14. ^ Mroczkowski, Dr. Robert S. (15 October 2004). "A Perspective on Connector Reliability" (PDF). IEEE. connNtext. Retrieved 1 July 2019.
  15. ^ a b "Essential Connector Terms and Definitions for Specifiers of Interconnect Wiring Systems" (PDF). Glenair, Inc. 2004. Retrieved 2019-06-25.
  16. ^ "Field Guide: Industrial Ethernet Connectivity". 2017.
  17. ^ Dietmar Röring. "M12 versus RJ45 Ethernet connection systems". 2014.
  18. ^ a b "Backshells by Amphenol Socapex" (PDF). RS Components Ltd. Amphenol Socapex. 2 November 2016. Retrieved 26 June 2019.
  19. ^ "Hybrid connector". Telecommunications: Glossary of Telecommunication Terms (FS1037C). National Telecommunications and Information Administration. 23 August 1996.
  20. ^ a b c Worley, Jon (31 July 2018). "Circular Connector Terminology Guide". NYK Component Solutions. Retrieved 2018-10-15.
  21. ^ Evans, Bill. Live sound fundamentals. Course Technology. pp. 24, 29. ISBN 978-1-4354-5494-1.
  22. ^ "How to Select the Proper Backshell" (PDF). CDM Electronics. 12 June 2012. Retrieved 26 June 2019.
  23. ^ David, Larry (17 March 2012). "Back Shell Definition". Electronic Engineering Dictionary Terms. Retrieved 30 June 2019.
  24. ^ "How to select a backshell" (PDF). Amphenol Corporation. BackShellWorld.com. 6 September 2008. Retrieved 26 June 2019.
  25. ^ a b c Lascelles, Robert (8 June 2015). "Modern Hyperboloid Contacts for Circular I/O Connectors". ConnectorSupplier.com. Retrieved 27 June 2019.
  26. ^ "IEH Hyperboloid Connectors" (PDF). IEH Corporation. October 2017. Retrieved 27 June 2019.
  27. ^ "Our Technology". IEH Corporation. Retrieved 26 June 2019.
  28. ^ a b David Brearley (9 October 2015). "Would you trust your life to a 50-year old connector design?". Connector Tips. Retrieved 27 June 2019.
  29. ^ SU application 1125684A1, Pustynskij Nikolaj, "Hyperboloid-shaped socket for connection device", published 1983 .
  30. ^ GB application 2366097A, Donald Richard Lacoy, "Hyperboloid electrical socket", published 27 February 2002 .
  31. ^ US patent 1833145A, Wilhelm Harold Frederick, "Connecter", published 7 July 1925 .
  32. ^ "Basic Pogo Pin Intro". C.C.P. Contact Probes Co. Retrieved 3 July 2019.
  33. ^ "Welcome to Qualmax". Qualmax. Retrieved 3 July 2019.
  34. ^ Slade, Paul G. (2014). Electrical Contacts: Principles and Applications (2nd ed.). CRC Press. p. 408. ISBN 978-1-4398-8130-9.
  35. ^ a b Huggins,, John S. (15 July 2009). "Jack/Plug – Jack, Plug, Male, Female Connectors". An Engineer's Review. Retrieved 1 July 2019.CS1 maint: extra punctuation (link)
  36. ^ a b Reference Designations for Electrical and Electronics Parts and Equipment: ASME Y14.44-2008 : Section 2.1.5.3 (2). ASME, Fairfield, NJ. 2008. Archived from the original on 2010-03-13. Retrieved 2012-02-03. the stationary (more fixed) connector of a mating pair shall be designated J or X ... The movable (less fixed) connector of a mating pair shall be designated P
  37. ^ Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters): IEEE-315-1975 (Reaffirmed 1993): Section 22. IEEE and ANSI, New York, NY. 1993.
  38. ^ "Crimp vs Solder: Pros and Cons". RF Connectors. 1 December 2004. Retrieved 1 July 2019.
  39. ^ a b "Crimp vs. Solder" (PDF). Aviel Electronics Catalog. 2013. Retrieved 1 July 2019.
  40. ^ "Field Installable: The secret to mastering connectors". Design Spark. RS Components. 16 March 2017. Solder connectors. Retrieved 1 July 2019.
  41. ^ Simon, Andre. "Solder Vs Crimping". High Performance Academy. Retrieved 1 July 2019.
  42. ^ "Datasheet 563: Cable Connector" (PDF). Clipsal. Retrieved 1 July 2019.
General
  • Foreman, Chris, "Sound System Design", Handbook for Sound Engineers, Third Edition, Glen M. Ballou, Ed., Elsevier Inc., 2002, pp. 1171–2.

External linksEdit

  Media related to Electrical connectors at Wikimedia Commons