Editing Electrical connector (section)

==Physical construction==
In addition to the classes mentioned above, connectors are characterised by their [[pinout]], [[#Methods of connection|method of connection]], materials, size, [[contact resistance]], [[Insulator (electricity)|insulation]], mechanical durability, [[IP code|ingress protection]], [[Service life|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.<ref name="zvei">{{cite book |url=https://www.zvei.org/fileadmin/user_upload/Presse_und_Medien/Publikationen/2016/November/Connectors_Technologies-and-Trends_engl/2016-11_Imagebroschuere_Steckverbinder_engl.pdf |title=Connectors – Technologies and Trends |date=August 2016 |publisher=ZVEI – German Electrical and Electronic Manufacturers’ Association}}</ref>{{rp|6}}

===Materials===
Electrical connectors essentially consist of two classes of materials: conductors and insulators. Properties important to conductor materials are contact resistance, [[Electrical conductivity|conductivity]], [[mechanical strength]], [[formability]], and [[resilience (materials science)|resilience]].<ref name="molex">{{cite web |url=http://www.piclist.com/images/com/marvin3m/www/http/connect/index.htm |title=Molex Connectors Explained, as used in Pinball |date=4 March 2005 |website=Marvin's Marvelous Mechanical Museum |access-date=1 July 2019}}</ref> Insulators must have a high [[electrical resistance]], withstand high temperatures, and be easy to manufacture for a precise fit

[[Electrode]]s in connectors are usually made of [[copper alloy]]s, due to their good conductivity and [[malleability]].<ref name="zvei" />{{rp|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]].<ref name="molex" /> 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.<ref name="gold-tin">{{cite web |url=https://www.connector.com/gold-or-tin-versus-gold-and-tin/#ixzz4irNbDrRT3 |title=Gold or Tin versus Gold and Tin? |website=Molex |last1=Endres |first1=Herbert |date=19 December 2011 |access-date=1 July 2019}}</ref><ref name="golden-rules">{{cite web |author=AMP Incorporated |title=Golden Rules: Guidelines For The Use Of Gold On Connector Contacts |date=29 July 1996 |publisher=Tyco Electronic Corporation |url=https://www.te.com/documentation/whitepapers/pdf/aurulrep.pdf |archive-url=https://web.archive.org/web/20180329092427/https://www.te.com/documentation/whitepapers/pdf/aurulrep.pdf |archive-date=29 March 2018 |url-status=dead |access-date=1 July 2019 |quote=Gold is generally specified as a contact coating for low level signal voltage and current applications, and where high reliability is a major consideration}}</ref>

Contact ''carriers'' that hold the parts of a connector together are usually made of plastic, due to its insulating properties. ''Housings'' or ''[[#backshells|backshells]]'' can be made of molded plastic and metal.<ref name="zvei" />{{rp|15}} Connector bodies for high-temperature use, such as [[thermocouple]]s or associated with large [[incandescent lamp]]s, may be made of fired ceramic material.

===Failure modes===

The majority of connector failures result in intermittent connections or open contacts:<ref name="navy">{{cite web |url=https://www.navsea.navy.mil/Portals/103/Documents/NSWC_Crane/SD-18/PDFs/Products/Connectors/ConnectorsFailure.pdf |title=Connectors: Failure Mechanisms and Anomalies |access-date=1 July 2019 |website=Naval Sea Systems Command}}</ref><ref>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.</ref>

{| class="wikitable"
|-
! Failure mode
! Relative probability
|-
| Open circuit || 61%
|-
| Poor contact || 23%
|-
| Short circuit || 16%
|}

Connectors are purely [[Passivity (engineering)|passive]] components{{snd}}that is, they do not enhance the function of a circuit{{snd}}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.<ref name="navy" /> Other causes of failure are connectors inadequately rated for the applied current and voltage, connectors with inadequate ingress protection, and threaded [[#Backshells|backshells]] that are worn or damaged.

High temperatures can also cause failure in connectors, resulting in an "avalanche" of failures{{snd}}ambient temperature increases, leading to a decrease in insulation resistance and increase in conductor resistance; this increase generates more heat, and the cycle repeats.<ref name="navy" />

[[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.<ref>{{cite web |publisher=[[TE Connectivity]] |url=http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Robotics/ENG_CS_82012_Ribbon_Cable_Interconnect_Sol_0412.pdf |title=Ribbon Cable Interconnect Solutions |page=30 |date=April 2012 |access-date=1 July 2019 |quote=By its design the traditional failure mode in tin plated connections, fretting corrosion, is prevented}}.</ref> 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.<ref name="reliability">{{cite web |url=http://ieee-holm.org/h2004/h2004antler.pdf |title=A Perspective on Connector Reliability |last1=Mroczkowski |first1=Dr. Robert S. |publisher=connNtext |website=IEEE |access-date=1 July 2019 |date=15 October 2004 |archive-date=25 October 2021 |archive-url=https://web.archive.org/web/20211025000712/https://ieee-holm.org/h2004/h2004antler.pdf |url-status=dead }}</ref> 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===
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 hardware#Connectors|USB]] or [[#Blade connector|blade connectors]]. They are commonly used for easier engagement and disengagement, tight environmental sealing, and rugged mechanical performance.<ref name="glenair">{{cite web |url=https://cdn.glenair.com/interconnects/pdf/intro2.pdf |title=Essential Connector Terms and Definitions for Specifiers of Interconnect Wiring Systems |publisher=Glenair, Inc |date=2004 |access-date=2019-06-25}}</ref> 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 connector|XLR]] and [[BNC connector|BNC]]. [[AC power plugs and sockets|AC power plugs]] are also commonly circular, for example, [[Schuko]] plugs and [[IEC 60309]].

[[File:N2K-CABLING.jpg|thumb|right|[[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.<ref>
[https://www.turck.us/static/media/downloads/WP_Industrial_Ethernet_Connectivity.pdf "Field Guide: Industrial Ethernet Connectivity"].
2017.
</ref><ref>
Dietmar Röring.
[https://www.mouser.com/pdfdocs/PhoenixContactM12_vs_RJ45_White_Paper.PDF "M12 versus RJ45 Ethernet connection systems"].
2014.
</ref>

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|backshells]], which provide physical and electromagnetic protection, whilst sometimes also providing a method for locking the connector into a receptacle.<ref name="amphenol-backshells" /> In some cases, this backshell provides a [[hermetic seal]], or some degree of [[IP code|ingress protection]], through the use of [[grommet]]s, [[O-ring]]s, or [[potting (electronics)|potting]].<ref name="glenair" />

===Hybrid connectors===
Hybrid connectors allow the intermixing of many connector types, usually by way of a housing with inserts.<ref>{{cite book |section-url=https://www.its.bldrdoc.gov/fs-1037/dir-018/_2625.htm |section=Hybrid connector |url=https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |title=Telecommunications: Glossary of Telecommunication Terms (FS1037C) |publisher=National Telecommunications and Information Administration |date=23 August 1996}}</ref> These housings may also allow intermixing of electrical and non-electrical interfaces, examples of the latter being pneumatic line connectors, and [[Fiber-optic connectors|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.