19th May 2022

What is an RJ45 connector?

What is an RJ45 connector?

Origins in telephony

Long before the world wide web came into existence and local area networks for computers had spread around the world, many if not most people in the USA didn’t even have a telephone at home and those who did just leased it from the Bell Company. The telephone network was still in its infancy in America, starting in the 1870s and steadily becoming more common by the 1940s. It owned not just the normally black and bulky telephones and handsets but all the wires on the poles, the switchgear in the central offices and the microwave links too. They had complete control over every aspect of their service delivery, and used their monopoly to build an amazingly integrated and durable system.

But there was a problem. And a big one. With all this power came responsibility and if anything went wrong with the customer’s phone it was Bell who had to fix it. A little boy in a moment of innocent curiosity once cut the handset cord with a pair of scissors. A technician from Bell had to come out and take the phone apart as well as the wall connection just to install a new handset cord. This was no quick replacement. Another time a dog chewed the cord between the set and the wall. Another technician was sent out on a mission. And this repeated over the entire network – all manner of unfortunate events. Even with no curious toddler or beloved pet, the phone cord would eventually fray and break, never mind if the bulky phone was designed to last for 40 years or more. What could be done to stop the phone company sinking ever more money into customer service calls?

A modular family was born

It was the late 1960s and AT&T was now on the scene. It ordered its engineers at Western Electric, its manufacturing arm, to focus their brilliant minds on the problem. The team, including Edwin Hardesty and Charles Krumreich eventually came up with the solution: a rectangular moulded plastic connector that had multiple parallel conductors, plastic channels to isolate and insulate each circuit, insulation displacement contacts in the plug, and springy wire contacts in the socket. A later design would replace the spring wire contacts in the socket with fixed blades.

Focusing on insulation displacement meant that field technicians could now mass terminate the connector with a simple crimp tool. The connectors were also easier to manufacture in the huge numbers required for a system-wide conversion. Moulding the plug body also meant that strain relief could be integrated into the plug, in the form of a flexible bar that would be crimped down onto the cord jacket after the electrical connections were made.

The design would be modified yet again, returning to spring wire contacts in the socket and replacing the original metal latch that locked the plug into the socket with a moulded plastic latch. But the basic design of the modular plug was now determined and ready for the future. The Trimline phone, where the handset now contained the dial or keypad, was one of the first phones to use the new connectors and throughout the 1970s, a decade of both cultural change and technological innovation, phone companies across the country retrofitted millions of existing phones.

In the 1980s the powerful AT&T monopoly began to break up and the new modular connectors now played an important role in democratising the entire phone system. For the first time customers could go into a store and buy whatever colour or style of phone they wanted, rather than leasing as before. One housewife went out and bought a new phone while her husband was at work. When he arrived home she had managed to rewire the new RJ11 connector into the wall using a special DIY kit promoted by AT&T.

Intuitive design, easy extensibility to more or fewer conductors, and the saturation of the market thanks to a large installed customer base all led to the modular connector being accepted across a wide range of industries. In 1976 the Federal Communications Commission mandated that phone system connections be standardised for interoperability so that customers could finally connect their own equipment to the telephone network.

The mandate termed these specifications registration interfaces, and the modular connectors became known as registered jacks, or RJ for short. The RJ11 became the connector for plugging a telephone into the wall and the handset into the telephone, while the RJ14 was designed for connecting multiple lines leading to a single phone unit. Crucially, an eight-conductor modular connector eventually became the standard for Ethernet connections. This was the RJ45. Its original 8P2C modular connectors were later modified into an 8P8C configuration with an additional tab or latch to ensure correct orientation in the newly arriving ethernet local area network (LAN) revolution.

An imaginary, networked world quietly in the making

The years passed and in 1995 at the dawn of The Internet, Mirek, the owner of a small computer software and network installation company in south-west Poland was going to change the world. In his office or inner throne room he plotted the expansion of his business. Across the grey carpeted floor a black telescope goldfish with bulging, distended eyes swam lazily in its bowl. It matched the black wall unit the bowl rested on. A wall clock ticked over a low glass coffee table, near two black leather sofas. Outside a sign fixed to the building showed the bright logo of his company accompanied by a globe encircled by parabolic connections. Giant cables soaring from the ground into space would enter the Earth at some point and then shoot off again to some other distant location, making a connection. This repeated many times. This crude but fantastical vision depicted a future networked world, using gargantuan cables. This was long before WIFI had become omnipresent or even thought of.

The vision came true

By 2005 the young entrepreneur had long left Poland for Chicago to pursue his career and dreams far away in the USA. His offices had been taken over by another company but that sign still hung outside on the building, waiting to be taken down. Now faded, the networked world could barely be seen. But those imaginary space cables had in fact gone on to envelop the world with countless terrestrial networks of interconnected computers all thanks to that original future proofed connector developed years earlier in a different technological age. Remember that years in the technological sphere are comparable to decades if not centuries in other domains.

Simple, adaptable and backwards compatible

The RJ45 consisted of both a male connector or plug attached to an ethernet cable and a matching female jack or port normally built into the back of a desktop computer or other internet enabled device. The magic of the RJ45 was its ability to be re-invented to support ever increasing data rates as well as be backwards compatible. Standardised in 1987, billions of these connectors have gone on to link up the world. Nowadays business people and travel bloggers travel the world with their laptops and can plug these into any hotel ethernet port that is available thanks to the ubiquity of the RJ45.

There are other factors that resulted in the success of the RJ45 connector. These include the low cost, solderless assembly of connector and wiring which enables fast production of custom cables, simple insertion and removal, easy field assembly using simple crimping tools, and the ability to customise cables on-site. Sockets or ethernet ports can also be orientated vertically or horizontally increasing their functionality. RJ45 connectors also feature an orientation tab or retaining latch to prevent incorrect wiring. Their 8-pin configuration also means that they can be used in more demanding and data-intensive applications.

The inner workings of the RJ45

Even if we haven’t wired, crimped and terminated, most of us have at some point plugged an RJ45 plug into the matching jack or ethernet port in our modem, router, PC or TV set top box at home, hearing it snap into place. It consists of a plastic housing, often transparent but can be opaque and coloured too.

Inside every RJ45 are eight channels containing gold plated contacts separated by insulating plastic as well as a gold plated contact pin with either two or three prongs. These prongs “bite” into the individual wires when you press down on the RJ45 with a crimping tool. Piercing the wire insulation and connecting with the conductor is a mechanism known as insulation displacement. 3 prong connectors will work with stranded and solid copper conductors whereas 2 prong connectors work with stranded copper only.

The eight colour-coded wires are unravelled from the four twisted pairs of the ethernet cable and gently pushed through the separate channels of the RJ45 plug, then bonded to the gold contacts with the crimping tool. T568A and T568B are two wiring schemes that are used to connect the cable to the RJ45 connector interface. T568A is generally considered a superior configuration as it offers wider backwards compatibility. However, T568B is more common, especially in older cables and equipment. The correct standard will depend on whether a straight-through cable (often called a patch cable) or a crossover cable is required. In most cases a patch cable will be used, which has the same type of wiring standard at each end. Crossover cable is much less common with a T568A connection at one end and a T568B connection at the other.

When the RJ45 is pushed into the ethernet port the male and female contacts connect with each other as the tab locks the plug tightly into place. Data and signals then begin to flow back and forth along the ethernet cable, delivering web pages from the distant servers and emails from the local computer operator as well as a plethora of other information.

Newer variants and challenging environments

There are now four common types of RJ45 connector: standard, staggered, shielded and ruggedized.

Standard RJ45 connectors have eight pins or contacts that are arranged side by side in a straight line and designed for CAT 5 ethernet cables.

Staggered versions are meant for the thicker wires of CAT 6 cables. The larger channels and holes for the wires wouldn’t fit inside the modular size of an RJ45 if placed side by side as in the standard version.

Shielded RJ45 connectors are encased in shiny metal plating to cancel or protect from the effects of EMI/RFI. They are used in longer cable runs and factory floors where the effects of EMI/RFI are more pronounced from noisy machines and other sources.

Away from the home or office and in more hostile and industrial environments, field RJ45 connectors are more robust with ruggedised housing and sealed to IP67 or higher ratings to render them waterproof. Here they find applications in industrial control panels, machine automation, portable testing and measurement equipment as well as robust computing devices. An IP67 rated RJ45 can be temporarily submerged in water while IP68 allows permanent submersion and IP69K will give protection from high pressure water jets used during for example equipment washdowns.

Category 7 cables can be terminated with RJ45 connectors, but these are specialised versions called GigaGate45 (GG45). GG45 connectors are however backward compatible with RJ45 connectors.


In summary the RJ45 connector enables stable and secure data transfer between devices and machines where wireless signals are not an option in certain environments or simply unavailable. It is also worth noting that even wireless routers or modems still need to be plugged into the network via a RJ45 connector so an ethernet cable is never far away at home or the office.

How can Live Electronics support users of dedicated RJ45 connectors?

Here at Live Electronics we are continually looking for the best products at the best price to help with modern technologies such as ruggerised and waterproof RJ45 connectors.


An RJ45 connector is primarily used to connect computers and other devices to a local area network (LAN) or The Internet, especially if a more stable and secure connection is needed.

The different types of RJ45 connector available, depending upon the application include:

Standard – 8P8C (8 position, 8 connection), non-shielded.

Shielded from EMI/RFI.  – internally shielded connectors that incorporate a shielding plate. May also be termed RJ48.

Ruggedized – include various external parts to protect the device from harsh environments.

RJ45 connectors can also be 2 prong or 3 prong. 3 prong connectors will work with stranded and solid copper conductors whereas 2 prong plugs work with stranded copper only.

In short, the answer is yes. The RJ45 port is the network port on a computer. This socket is also known as the Ethernet port, the network adapter, the network jack or the RJ45 jack.

No, Cat 5 or more commonly Cat5e connectors have a straight pin layout whereas Cat6 connectors have a staggered pin layout. This is because the staggered layout is beneficial in reducing cross-talk interference. In conjunction with the design of Cat6 cable, this enables higher data transfer speeds of max 10Gbps up to 55 metres compared with 1Gbps at 100m for Cat5e.

RJ45 connectors feature eight pins to which the wire strands of a cable interface electrically. Each connector has eight locations spaced about 1 mm apart into which individual wires are inserted using special cable crimping tools. When the RJ45 connector is plugged into the ethernet port data begins to flow back and forth bringing the screens and devices to life.

The male connector or plug of the RJ45 is pushed into the female socket or jack, also known as the Ethernet port, the network adapter, the network jack or the RJ45 jack. RJ45 connectors are designed with a latching mechanism that secures the physical connection. As the connector is inserted into the socket, a plastic tab on the connector locks against a ridge in the socket so that the plug cannot be removed without disengaging the tab by pressing it against the connector body.