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Connectors are used to separate and connect electrical lines or, for example, lines for optical radiation (generally technical media ). The connecting parts are appropriately aligned by means of a form fit of the plug parts, fixed releasably by spring force ( contact foot ) and often additionally secured against unintentional loosening by screwing . Connectors are a branch of connection technology . There are many standardized connectors around the world.

A distinction is made between standards for the geometric shape of plugs, sockets , couplings and sockets and standards for the electrical or optical signal that is transmitted via cables or optical fibers and connectors.

Basic designs

Coupling (“female”), plug (“male”) and socket (“female”) using the example of DIN connectors
PCB with direct connector

In the case of electrical plug connections, a distinction is made between the male part of a plug connection (with outward-facing contact pins) and the female part (with inward-facing contact openings). The male part, in turn, is a plug if it belongs to one end of the cable, or a built-in plug if it is intended for permanent installation in a device housing. The female part is a coupling if it belongs to one end of the cable, or a socket if it is intended to be permanently installed in a device housing. Flat plug connectors are regularly used for mains voltage connections within electrical appliances as well as in the automotive sector, which are crimped onto the wire ends of the cable harness as cable lugs using the crimping or pressing process and are both insulated and completely uninsulated.

There are also connectors with plug-in elements of both sexes or those for electrical current, radiation or media in a common plug housing.

A distinction is made between direct and indirect connectors for printed circuit boards . With direct plug-in connectors, the plug-in contacts are specially shaped conductor tracks . In the case of indirect plug connectors, special plugs are soldered on, the pin strips or tab strips . The counterparts of the direct connectors on the printed circuit boards are referred to as spring strips , they are practically socket strips.

Connection to board or cable

Connectors on a circuit board are usually soldered to the circuit board using straight or angled solder pins. In many cases this also covers the mechanical fastening. If greater mechanical robustness is required, a shielding plate, for example, is soldered several times to the circuit board mass; in a second stage, additional rivet or screw connections to the circuit board are used.

Cables or jumper wires are either soldered to soldering lugs on the connector or screwed in during house installation, or the connector is pressed onto the cable using insulation displacement technology in the case of multi-core flat cables . Alternatives to soldering technology are massive press-fit technology, wound connections or direct plug-in technology.

Mechanical lock

VGA connector with screw lock next to the actual contact field
USB plug with cutouts to snap into the socket

If heavy cables have to be connected, the holding force of the inserted electrical connection pins cannot guarantee the mechanical stability of the plug connection. In these cases an additional mechanical connection is made.

For connections within housings, a simple snap-in technique is often used, which can also be easily removed manually.

With external connections, locking by means of screw connections predominates, as is common with D-Sub connectors, for example . Another type of screw connection exists for professional versions of DIN connectors that work with a union nut. In addition, the Centronics interface, for example, has a locking mechanism with spring wire loops and a connection that gently engages with spring force, as is the case with USB plugs . With jack plugs , this locking function is already integrated in the contact part. In the case of high-frequency connections, such as the BNC plugs, there is also a bayonet lock . For three-phase and high-voltage connectors, there are a number of bolt and clamp mechanisms.

Contact resistance

Depending on the application, special requirements must be placed on the contact resistance. This also includes the reliability of the (low) contact resistance over long periods of time or over a large number of connections or during mechanical movements. In the case of small useful voltages, the fritting stress must also be largely avoided.

The contact pressure and the contact area are also important for the contact resistance. A large contact area is not always beneficial because then there is no contact pressure and / or the contact only takes place at certain points. Cold welding can also be used.

Connector housing

Plugs and couplings are often bare for internal connections. However, when it comes to external connections, it is advisable to disguise the contact point for several reasons:

  • Contact protection: On the one hand, a user or other cables or devices should be prevented from coming into contact with potentially dangerous voltages, on the other hand, the conductors should be protected against unwanted connections with other signals or potentials. This encapsulation also provides a certain level of protection against dust and corrosion (see for example industrial PC ).
  • Strain relief : Heavy cables should not pull directly on the electrical contact point, as this is not designed for this and could fail in the long term. The outgoing cable is therefore oftenclampedby crimping or screw terminals within the connector housing so that the forces can act in a defined manner at this point.
  • Mechanical strength: When you loosen a connector, you shouldn't pull on the cable (even if there is a strain relief), the connector should be shaped so that it is easy to grasp and handle. In addition, the surface is often corrugated in order to transfer tensile forces better.
  • Shielding : In the case of audio and high-frequency connections in particular, it is important to shield signal lines from interference. The connector housing contains a closed metallic shield for these cases. Usually it consists of separate parts that are enclosed in outer insulating plastic parts. In the case of DIN plugs, there are variants with a single tubular shielding part into which the actual contact part is inserted, as well as variants with two metal half-shells that are only held together by the outer plastic part pushed over them. The strain relief is also often integrated into the shielding part, which is electrically connected directly to the outer shielding of the outgoing cable. In the case of XLR plugs (AUDIO), however, a connection between the connector housing and the shield / ground is explicitly rejected. The routing of the ground potential via the connector housing and a plug contact formsground loops .

In the case of mass production, the connector housings are often produced simply by overmolding the contact part with plastic. A metallic shield case is missing. Metal foils (possibly with an insulated coating) are rarely used. Crimping also occurs. When assembling for later detachability, there are the variants of sliding on with locking or screwing together.


In addition to the plug-in contacts, some plug-in connectors also contain non-conductive grooves and pegs, which mean that the plug can only be inserted in a certain position. This is called coding.

Switch sockets

Switching socket (NC contact) with inserted jack plug

Some built-in sockets are combined with an electrical switch that is actuated when the plug is inserted. In this way, a device can easily adapt to whether a connection has been established or not. The mechanics of the switching contacts are largely similar to that of electromechanical relays .

In the case of diode plugs, actuation takes place through the surrounding metal shielding sleeve. In the case of jack plugs, the central contact pin pushes a mechanical lever aside, in the case of power supply plugs, the outer sleeve.

A common use is for headphone connections : When a headphone cable is connected, the connection to a built-in loudspeaker is interrupted by the switch socket . The special square plug can be inserted in two orientations offset by 180 °, whereby the switch only silences the loudspeaker in one of the positions, but not in the other thanks to a recess, so that this functionality is made available to the user.

In the case of power supply plugs, the connection to an internal battery is interrupted when a plug-in power supply is plugged in; when the battery is supplied , these are then charged. For further applications see under device plug .

Power supply

Single-phase household connector systems

Single-phase household plugs are plugged into the socket and are used for the electrical detachable connection of flexible device connection lines with the power supply of the house installation. They are used, for example, on lights , office equipment and small machines in industry. The distance between the socket and the device can be increased with the help of extension cables . On the device side, so-called device plugs are sometimes used to connect the device to a flexible cable, unless it is hard-wired.

Household plugs are internationally classified as types A to M. This classification comes from a publication by the American Department of Commerce and has become established worldwide. Unfortunately, this classification of the connectors does not deal with all the differences between the connectors commonly used around the world; There can therefore be several variants of one connector type, some of which are not compatible with one another.

  • PowerCon , often used in stage technology (proprietary)
  • Plug according to DIN 56905 , almost exclusively in stage technology, forerunner of PowerCon
  • Terko for direct or alternating current, reverse polarity protected (proprietary)

Single and multi-phase low voltage systems

Plug connection with Anderson Powerpole plugs
  • Plugs according to IEC 60309 , like the 5-pin CEE three-phase plug connector for 16 to 125 amps, see here
  • In Germany, Austria, the Netherlands and Sweden: Perilex for three-phase current in accordance with DIN 49445 (16 A socket) and DIN 49446 (16 A plug), DIN 49447 (25 A socket) and DIN 49448 (25 A -Plug)
  • In Switzerland: three-phase connectors for low currents for household, trade and industry according to SEV 1011 , (T15 for 10 A and T25 for 16 A). Corresponding sockets can also accept single-phase plugs.
  • Anderson Powerpole , system with hermaphroditic plugs up to 600 volts and 310 amps

In the GDR there were 4-pin power plugs until the 1970s, which were also referred to as Grimma plugs after the production site in Grimma in Saxony . They were standardized according to TGL 4175 and were manufactured in 4 types for currents from 25 to 100 A. The disadvantage was that they do not have a neutral conductor contact and their use was therefore limited to symmetrical loads such as three-phase motors. Interconnecting the neutral conductor and protective conductor to the PEN or earlier SLN, as was sometimes the case with these plugs, is not permitted for new installations and flexible connection cables and may also trigger the FI circuit breaker. In Austria similar-looking plugs standardized according to DIN 49450 , but mechanically incompatible, were common until the early 1980s.

Furthermore, according to TGL 200-3763, there were 5-pin oval connectors (RST, N, leading PE) in Bakelite housings for 10 amperes.

Low voltage plug

Low-voltage plugs are used to supply low, harmless voltages ("functional extra-low voltage"). For this, however, they sometimes work with very high currents (ATX connector up to 120 A).


Laboratory connectors are connectors for single conductors for the construction of test circuits. The most common are banana plugs with a nominal diameter of 4 mm, which are available in contact-protected and non-protected designs. Similar connector systems are also available with 6 mm and 2 mm nominal diameters.

Furthermore, so-called plug -in boards are also used to set up more complex circuits , in which bridges made of solid wire serve as a plug-in connection on a base plate, which has a large number of partially interconnected sockets. The sockets can also be used to hold wired components and circuits ; for this they are arranged in a 2.54 mm grid.

In addition, there are so-called alligator clips that, depending on the version, can be pushed onto a 4 mm banana plug or contacted directly with a conductor (screw or crimp connection).

BNC connectors are common for coaxial connections .


  • Cinch : separate for right and left unbalanced stereo signals
  • DIN connectors , also known as diode connectors , exist in mono and stereo versions, are out of date and are also used for other purposes
  • Pickup plug for old tube radios
  • Loudspeaker connector and measuring device connector, two very similar, also outdated connectors
  • Jack plugs are two-pole for mono signals, three-pole for stereo signals and four-pole for headsets ; More than four-pole plugs are prone to deformation due to their design and are very rare and are often replaced by several individual plug connections and, if necessary, bundled with D-Sub plug adapters
  • TOSLINK , optical connector
  • XLR in the recording studio and stage area
  • Speakon speaker connector
  • Multipin for mixing consoles and stage boxes
  • Small and large Tuchel , older microphone plugs
  • D-Sub connector: In the PC area, device-specific adapters ( breakout cables ) are often connected to professional sound cards in order to enable the connection of standard connectors (e.g. cinch, DIN, jack, XLR) that would otherwise not be available for reasons of space could be connected

Analog video signal

With the composite signal (FBAS) there are three qualitatively graded plug connections:

For S-Video signals:

Video signal via radio frequency connection:

  • Belling-Lee connector (better known as antenna cable )
  • F connector in satellite systems for the transmission of the satellite intermediate frequency between the dish and receiver

In computer technology:

Digital video signal

High frequency


Plug for modules

PC card and PCMCIA connectors

For modules used in higher-level housings (e.g. plug-in modules in subracks for 19-inch racks , plug-in cards in computer housings ), connector strips are used, with part of the connector protruding from the module, while the counterpart is installed in the receiving housing, so that the electrical connection is contacted more automatically when the module is installed (indirect plugging) or the module is installed by plugging.

Note: The term modular connector stands for the RJ connector; therefore the word modular connector is sometimes also used to denote RJ connectors.


Travel adapter France

For other telephone systems see article Telephone socket .

See also:

Commons : phone adapter  - album with pictures, videos and audio files

optical fiber

  • SC connector
  • ST connector
  • LC connector
  • E2000 connector
  • FC / PC
  • FSMA
  • MTRJ connector
  • ESCON connector
  • Mini BNC
  • Mini SC
  • URM P2 connector
  • TOSLINK (audio data)
  • M12-FO (IEC 61754-27)

Automotive industry

Model railway

  • RJ-45 or Ethernet connector (feedback)
  • RJ-12 connector (digital control)
  • s88 connector (feedback)
  • 2.6 mm plug (various consumers)
  • special connector from the manufacturer z. B. Märklin , Kleinbahn (2 mm)
  • NEM locomotive decoder plug

Web links and individual references

Commons : Electrical Connectors  - Collection of images, videos, and audio files

Individual evidence

  1. . In: Retrieved November 26, 2014.
  2. Assembly instructions for VEB Elektroschaltgeräte Grimma (ESG)