Choosing circular connectors for automation

A guide to choosing circular connectors for automation and control applications

The term circular connector refers to any multi-pin electrical connector with a circular mating surface and a cylindrical contact housing. Used for cable-to-panel and cable-to-cable interfacing, circular connectors are a popular choice for industrial automation and control applications because they are easy to connect and disconnect, can function reliably in harsh environments, and offer an extensive range of current and voltage ratings. A great many connector configurations are available, so choosing the most appropriate connector for a particular application is not always straightforward. This article considers some of the main selection criteria.


Connector components

A significant advantage of circular connectors is that one type of shell can accommodate many different pin configurations, including signal, coaxial and power contacts. Rather than keeping an extensive and costly inventory of preassembled connectors, designers can make up custom connectors from an inventory of frequently used components including:

  • Individual contacts: male and female, with various sizes, plating materials, current and voltage ratings, and termination methods (e.g. crimp, solder, wire wrap) for different wire sizes.
  • Adapters: plug or socket connector bodies in various materials, sizes and orientations (straight, right-angle, etc.) that accommodate the contacts and provide the mating interface.
  • Inserts that separate and isolate the individual contacts within the connector body.
  • Backshells to provide shielding, strain relief and environmental protection for the cable-connector interface.
  • Various seals, gaskets and flanges for mechanical and environmental protection.


Specifying a circular connector

When choosing a circular connector for a particular application, there is a wide range of variables to consider. Among the first are the number of contacts, which can be up to 128, and the type and size of wire to which they will be attached. Current ratings up to 80 A and voltage ratings up to 1500 V are available.

The operating environment should be considered early on. Environmental resistance is usually specified using a two-digit IP (“internal protection” or “ingress protection”) code where the first digit (from 1 to 6) represents protection against solid particles and the second (from 0 to 7) represents protection against water. For example, IP67 and IP65 both protect against dust ingress, but the former is resistant to temporary immersion in water while the latter only resists jetting (water jet from any direction).

It is necessary to assess how much space is available for the connector, bearing in mind the degree of environmental protection required. A wide range of shell sizes is available, including IEC standard M8, M12, M23 and M40, and others up to 68 mm.  Connector size is often specified to IEC standard M8, M12, or a range of size groups including standard, miniature and micro. Choice of body orientation is another option to help fit a connector into a given space.

Connector mounting configurations include panel, cable and flange mount, free hanging, and through hole. For robust connectivity, a variety of latches, locks, key and thread configurations may be specified. Strain relief options are also available.

The RS Components industrial/automation circular connector database helps to ease the selection process by allowing you to search on the above parameters and more.


Coupling formats

The two sides of an electrical connector interface are usually specified by gender, but working out what “male” or “female” actually means can be fraught with difficulty. Generally, male and female connectors are those with pins and receptacles, respectively, and may also be referred to as plugs and sockets. However, “plug” is often also used for a “free” or mobile cable-mounted connector, and “socket” for its fixed panel mounted counterpart. For multi-contact electrical connectors, the male contacts tend to be the most fragile components and so are often recessed within the panel mounted connector for protection. However, the recess resembles a socket into which the cable-mounted plug is inserted, so the connector with male contacts may be referred to as female and vice versa.

Connector vendors approach this problem of definition in different ways. One of the leading manufacturers, TE Connectivity (formerly Tyco Electronics), categorises its circular connectors as “standard gender” — male connectors having female contacts and vice versa — and “reverse gender” — in which male connectors have male contacts. It is always worth noting the gender of not just the connector body but also the contacts it is designed to accommodate.


CPC series for industrial applications

Widely used in industrial and control applications — notably production equipment, instrumentation, human-machine interfacing, motion and drives, robotics and power distribution — is TE Connectivity’s AMP CPC (circular plastic connector) range. These are modular connectors with removable contacts and a replaceable coupling ring for ease of repair in the field (see Figure 1 below).

Figure 1: TE Connectivity’s AMP circular plastic connector range

The connector body is made from heat resistant, self-extinguishing thermoplastic, while the shell can be either plastic or metal.  CPCs are quick to connect and disconnect, with thread assist, and have inbuilt pin and socket protection.

CPC Series 1 refers to “standard-density” CPCs supporting multiple combinations of signal and coaxial contacts in 4 to 37 positions. Sealable to IP67, they can carry a maximum current of 13 A when crimped using Size 16 Multimate III contacts. Solder and posted contacts are available for PCB applications.

CPC Series 2 is a range of high-density connectors accommodating Size 20 precision formed or screw machined contacts in up to 63 positions, at a maximum current capability of 7.5 A. CPC Series 3 power connectors can carry up to 25 A per standard Type XII contact, or 60 A per high-current screw machined contact; 3-pin and 7-pin configurations are available. Series 4 CPCs accept both standard Size 16 Multimate and Type XII power contacts, with 13, 16 or 22 positions available. CPC Series 5 and 6 are made up of, respectively, power and combination power-and-signal connectors, all environmentally sealable to either IP65 or IP67 specifications.

Series 1 to 4 CPCs of certain sizes are available in metal-shell (also known as CMC) versions consisting of a thermoplastic insert in a nickel-plated zinc alloy shell. An optional interface seal provides splash protection between the metal shells on either side of the interface.