Modular connector

A modular connector is a special kind of electrical connector used in many electronic devices and appliances. You might find these connectors in things like computers, phone networks, audio headsets, and more.

These connectors were first made for telephone sets in the 1960s by the Bell System. Later, in 1976, the Federal Communications Commission created a system to register different types of these connectors, calling them registered jacks. Because they were easy to use and already available, designers started using modular connectors in many other places instead of the older, bigger connectors.

Today, modular connectors are very common. They are probably most well known for use in telephone and Ethernet connections, but they are used in many other ways too. There are different rules for how these connectors should work in various applications, making sure they fit and work correctly.

Nomenclature

Modular connectors are often called modular phone jack and plug, RJ connector, and Western jack and plug. The name modular connector comes from its first use in telephone equipment by the Western Electric Company in the 1960s. This includes the 6P2C used for telephone line connections and 4P4C used for handset connectors.

Registered jack names tell us about the signals and wiring used for voice and data at places where people connect to the public switched telephone network (PSTN). People often use the registered jack number to talk about the physical connector itself; for example, the regular 8P8C modular connector is often called RJ45 because the registered jack standard RJ45S described a similar, but changed, 8P8C connector. In the same way, different six-position modular connectors may be called RJ11. Also, the 4P4C connector is sometimes called RJ9 or RJ22, even though these official names do not really exist.

History

The first small modular telephone connectors were made by AT&T in the mid-1960s for use with the Trimline telephone. As more people wanted to use multiple phones in their homes, the Bell System began selling kits and phones that customers could connect themselves in the early 1970s.

By 1976, these connectors were officially standardized in the United States by the Federal Communications Commission (FCC), which created a set of rules called Registered Jack (RJ) specifications to help connect phones and other devices to the telephone network.

Gender

Modular connectors have something called gender. Plugs are called male, and jacks or sockets are called female. Plugs are used at the end of cables and cords, while jacks are used in fixed spots like walls, panels, and equipment. Usually, cables have a plug on one end and a jack on the other, but they are often connected using a special piece that links two jacks together.

Latching tab and orientation

Most modular connectors have a special part called a latching tab. This tab helps keep the connector firmly in place. When you plug it into a socket, the tab locks into a ridge, so it doesn’t fall out easily. To remove it, you just press the tab to unlock it.

Sometimes, a plastic cover called a boot is added to protect the tab. This boot stops the tab from catching on other cords or rough edges, which could break the tab. Cords with this boot are called snagless and are made by putting the boot on before finishing the connector.

Size and contacts

Modular connectors are described with two numbers showing how many spots they have for contacts and how many contacts are actually used. For example, a 6P2C connector has six spots and two contacts. Sometimes the letters are left out, and the numbers are separated by an x (6x2) or a slash (6/2).

These connectors come in four sizes, with four, six, eight, or ten spots. The smaller ones have different widths, while the larger ones share an even wider body.

Inside the connectors, there are sharp parts that connect with the wires by pushing aside the wire covering — this is called insulation displacement. Cables can have solid or stranded wires (tinsel wire), and each type of wire needs a special kind of connector. Using the wrong type can lead to poor connections.

Some special plugs have extra slots to fit into wider jacks without causing damage. These plugs might be a light bluish color or have extra slots to help tell them apart. They are useful for testing equipment.

Termination

Terminating cables with modular connectors works in a similar way no matter how many positions and contacts the plug has. A special crimping tool has a part called a die that matches the shape and number of pins on the plug.

The die in the tool looks like an 8P8C jack but has eight teeth on top. When you use the tool, the die squeezes the plug, pushing the pins into the cable’s wires. The tool also shapes part of the plug to hold the cable tightly for extra support and strain relief. This process attaches the plug to the cable permanently.

Pinout

The way the contacts are arranged in modular connectors, called the pinout, can change depending on what they are used for. For telephone connections, there are standard rules. For Ethernet cables, the rules are set by the ANSI/TIA-568 standard. But for some other uses, like with RS-232, there are many different ways people might set it up. Because of this, adapters that connect D-sub to modular connectors often come with the D-sub parts ready but not put into the connector, so you can decide how to match them up.

4P4C

The four-position four-conductor (4P4C) connector is the standard connector used on both ends of telephone handset cords, and is often called a handset connector.

Handsets and headsets for telephones commonly use a 4P4C connector. The two center pins are used for the receiver, and the outer pins connect the transmitter. This setup ensures that flipping the cord does not affect how the signal travels. The Macintosh 128K, Macintosh 512K, Macintosh Plus from Apple, and the Amiga 1000 from Commodore use 4P4C connectors to link the keyboard to the computer. These connectors supply power to the keyboard and receive data signals. Some DirecTV set-top boxes also feature a 4P4C data port with an adapter to connect to a computer serial port.

6P

Modular plugs are named based on how many spots they have and how many pins are put in those spots. The 6P2C, 6P4C, and 6P6C plugs are well known for connecting to RJ11, RJ14, and RJ25 jacks. Even though they all use the same six-spot connector body, they have different numbers of pins.

RJ11 is used for one telephone line, RJ14 for two lines, and RJ25 for three lines. RJ61 is for four lines but uses an 8P8C connector.

8P8C

The 8 position 8 contact (8P8C) connector is a type of connector used for cables in many electronic devices. It is often used for things like computer networks, telephone lines, and communication devices. This connector has eight metal parts that touch each other to make an electrical connection.

Although often called RJ45 in networking, the name RJ45 originally described a specific way to connect telephone wires. Today, 8P8C connectors are used in many ways, following standards that make sure they work well for different types of connections. They can be used for both telephone and computer networks, and they are made to work reliably at high speeds.

Pin	T568A pair	T568A color	T568B pair	T568B color	10BASE-T/100BASE-TX signal	1000BASE-T/10GBASE-T signal	Wire	Diagram
1	3	white/green stripe	2	white/orange stripe	TD+	DA+	tip	Pin numbering on plug face. Connected pins on plug and jack have the same number.
2	3	green solid	2	orange solid	TD−	DA−	ring
3	2	white/orange stripe	3	white/green stripe	RD+	DB+	tip
4	1	blue solid	1	blue solid	not used	DC+	ring
5	1	white/blue stripe	1	white/blue stripe	not used	DC−	tip
6	2	orange solid	3	green solid	RD−	DB−	ring
7	4	white/brown stripe	4	white/brown stripe	not used	DD+	tip
8	4	brown solid	4	brown solid	not used	DD−	ring

10P10C

The 10P10C connector is often called an RJ50 connector, even though this name was not an official standard. It has 10 spots to connect and 10 actual connections. People mostly use the 10P10C connector in special systems for moving data.

Standards

There are many rules and standards that help make sure these connectors work well and safely. Some important ones include:

• ANSI/TIA-968-A: Telephone terminal equipment: Technical requirements for connection of terminal equipment to the telephone network (archived 2018-09-28))
• ANSI/TIA-1096-A: Telecommunications telephone terminal equipment connector requirements for connection of terminal equipment to the telephone network
• IEC 60603-7-1: Connectors for electronic equipment: Part 7-1: Detail specification for 8-way, shielded free and fixed connectors with common mating features, with assessed quality
• IEC 60603-7-2: Connectors for electronic equipment: Part 7-2: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 100 MHz
• IEC 60603-7-4: Connectors for electronic equipment: Part 7-4: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz
• IEC 60603-7-5: Connectors for electronic equipment: Part 7-5: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz
• IEC 60603-7-7: Connectors for electronic equipment: Part 7-7: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 600 MHz
• ISO/IEC 8877, EN 28877: Information Technology—Telecommunications and Information Exchange between Systems—Interface Connector and Contact Assignments for ISDN Basic Access Interface Located at Reference Points S and T
• US government documents define registered jack applications of modular connectors for telecommunications. See Registered jack § History and authority