Modular connector
From Wikipedia, the free encyclopedia
Modular connector is the name given to a family of electrical connectors examples of which are pictured. These connectors were originally used in telephone wiring and are still prevalent for that, but are used for a variety of other things. A modular connector's advantage over many other kinds of connectors is its small size and ease of plugging and unplugging. Many uses that originally used a bulkier connector have migrated to modular connectors. Probably the most well known applications of modular connectors is for telephone jacks and for Ethernet jacks, which are nearly always modular connectors.
The modular connector was first used in the Registered Jack system, so there are precise specifications of them within the Registered Jack specifications. Those are the specifications to which all practical modular connectors are built. However, the Registered Jack specifications don't name the physical connectors. Instead, these are covered by ISO standard 8877, first used in ISDN systems.
Modular connectors have gender. The male connector is called a plug, while the female connector is called a jack or sometimes a socket.
Modular connectors come in four sizes: 4-, 6-, 8-, and 10-position. A position is a place that can hold a conductor (pin). The positions need not all be used; a connector can have any even number of conductors. Unused positions are usually the outermost positions. The connectors are designed so that a plug can fit into any jack that has at least the number of positions as the plug. Where the jack has more positions than the plug, the outermost positions are unused. However, plugs from different manufacturers may not have this compatibility, and some manufacturers of eight position jacks now explicitly warn that they are not designed to accept smaller plugs without damage.
Some connector types in the family are indexed, which means their shape is altered from the standard somewhat to prevent them from mating with standard connectors. The indexing is usually a different shape or position of the hook, but can also be an additional tab.
The members of the family are typically identified using the format "[number]P[number]C", e.g. "6P2C", which means 6 positions, 2 conductors. Alternate formats "[number]x[number]" (e.g. "6x2") or "[number]/[number" (e.g. "6/2") are also used.
Modular connectors lock together. A spring loaded tab called a "hook" on the plug snaps into a jack so that the plug cannot be pulled out. To remove the plug, you have to press the hook. The most common way to install a jack in a wall or panel is with the hook side down. This usually makes it easier to operate the hook when removing the plug, because the person grabs the plug with thumb on top and presses the hook with the index finger. The positions of a jack are numbered left to right, looking into the receiving side of the jack with the hook side down, starting at 1. The positions of plug are numbered the same as the jack positions with which they mate. The number of a conductor is the same as the number of the position it's in. So for example in a 6P2C plug, only conductors 3 and 4 exist.
The pinouts (assignment of function to each conductor) are as varied as are the applications of modular connectors. Even within the same application, there is often little standardization. For example, there are multiple conventions for use of 8P8C for RS-232. As a result, when you buy a DE9 - 8P8C adapter, it usually comes without the pins installed -- you insert them according to the particular standard you're using. The telephone pinouts are well standardized as the registered jack system. The Ethernet pinouts are also well standardized as TIA/EIA-568-B.
The application of jack versus plug is generally based on physical installation only. Jacks go in walls and panels, while plugs go on wires. This is in contrast to some other connector systems where the gender is related to the function of the connector (e.g. in a power cabling system, a female connector delivers power while a male connector receives power). Extension cables (male on one end, female on the other) are rarely seen; instead, people use male-male cables and female-female couplers.
Modular connectors also go by the names "modular phone jack/plug", "RJ connector," and "Western jack/plug." The 8P8C modular connector type is often called RJ45, but the name "RJ45" is also used for something quite different. The "modular connector" moniker is not terribly descriptive, but arose from its original use in a novel system of cabling designed to make telephone systems more modular.
Modular connectors were originally invented and patented by Bell Telephone Laboratories (patent filed 6 July 1973; U.S. Patent 3,860,316 issued 14 January 1975), and replaced the hard-wired connections on most Western Electric telephones around 1976. At the same time, they began to replace screw terminals and large 3 and 4 pin jacks in buildings.
A disadvantage of modular connectors is that the fragile hook on a plug easily snags and often breaks when you try to pull a cord through other cords and other obstructions. Some higher quality cables have a flexible sleeve called a "boot" over the plug, or a special hook design, to prevent this. Boots are seen mainly on 8P8C data cables.
See also Telephone plug
