RJ45: all about the network connector

RJ45 connector

Ethernet networks and router and modem cabling often use the physical RJ45 connector. All commercial cabling and telecommunications products under the 3 EIA / TIA-568-B standards have adopted it as a connection. Therefore, it is one of the most popular link connections that exist today, despite the fact that wireless networks have become popular in homes and offices, but are still used for a multitude of applications.

EIA (Electronic Industries Alliance), an association of electronics and technology companies in the United States whose purpose is to develop and promote competitiveness in this industry, was commissioned to create the RJ45 (Registered Jack). And despite its popularity today, it is not a recent connector, in fact, its first revision was made in 1991. By the way, you should not confuse it with other similar ones such as the RJ11 (smaller size and different characteristics).

Pinout and RJ45 connection

RJ45 with 568B connection

El RJ45 It has a plastic structure, normally transparent (there may be other colors), which contains 8 metal pins for the connection. In addition, it has a kind of semi clamp with a tab that fits into the port so that it does not move or come loose, since being a connector that will support data transfers, it must be secured.

As for the connection of your cables, they can be done in two ways. One of them is using a crimper stripping the ends of the wires and connecting them manually. Another is through an automated industrial process, which is used for cables produced by manufacturers. However, surely, if you work with this type of network equipment, surely you have ever had to do it manually to create a twisted pair for example ...

Cables have their color code and its meaning:

Pin Acronym Name Easier Standard 568A Standard 568B Standard Variant A (Gigabit) Standard Variant B (Gigabit)
1 TX + Transceive Data + Positive data transceptive thread White and green White and orange White and orange White and green
2 TX- Transceive Data - Same as above but negative finanacing Orange Orange finanacing
3 RX + Receive Data + Thread to receive positive data White and orange White and green White and green White and orange
4 BDD + BiDirectional Data + Bidirectional positive data Blue Blue Blue White and brown
5 BDD- BiDirectional Data - Bidirectional negative data White and blue White and blue White and blue Brown
6 Rx- Receive Data - Same as RX + but negative Orange finanacing finanacing Orange
7 BDD + BiDirectional Data + Other BDD + White and brown White and brown White and brown Blue
8 BDD- BiDirectional Data - Other BDD- Brown Brown Brown White and blue

* There are different standards, according to them you can have one or another color code ... You have to pay attention to that to connect them correctly.

Connection types

RJ45 cross connection

The cable connections that I have described in the previous section can be made in several possible ways, thus varying the application for which the RJ45 cable is to be used. The ways to connect them are:

  • Direct: the same order of pins is respected at both ends, that is, it will be connected the same in the two RJ45 that we have in a cable. In this case, you can connect devices that are unequal, for example a PC and a switch, or a PC and a hub, etc.
  • Crossed: very popular in applications to connect two equal devices in a network to be able to transmit data between them without an intermediate device. For example, you could connect two PCs directly through their network cards with a crossover cable. To do this, the RX and TX cables have to be crossed, so that when a PC transmits through the TX it is received by the other PC through RX, and vice versa.

You know that to connect them you would need a special crimper, the normal electricians are not worth to strip power cables. In this case, it is a crimper that has a specific tool for RJ45. But the way to connect it is very simple as can be seen in this video:

Cable types

In this section we will see ltypes of cables that we can have for an RJ45 connector.


UTP, FTP and STP from RJ45

For the RJ45 you can find various types of cables in stores. They vary depending on the internal architecture and the type of application for which each of them stands out:

  • UTP- Designed to be combined with unshielded twisted pair cable. Their price is very low and they are easy to use, but they can produce more errors than other types of cables and have limitations to work over long distances without signal regenerators. Therefore, they would be good for connecting nearby devices and where errors are not critical.
  • FTP- Designed to be combined with global shielded twisted pair cable. This protection greatly improves the reliability of the cable for transfers, since they generate a screen similar to that of the coaxial cables of TV antennas. Its impedance is 120 ohms. They will be a bit more expensive than UTP, but are better for longer distances and where errors are more critical.
  • STP: designed to be combined with a special version of twisted pair cable that uses metallic shielding to screen and shield the cable (of each pair and of the whole assembly). It is the most expensive of all, but also the one that gives the best results.


RJ45 female and male

As well there are categories for these connectors:

  • Category 5: it was designed to transmit at frequencies of 100Mhz, providing a transfer speed of 100Mbit / s. Use two twisted pairs with a maximum range of 100 meters. Over time it evolved and a category 5e was introduced that conformed more to the standards, theoretically increasing the speed up to 350 Mbit / s. For that, new twisted pairs were needed (4). So assuming the conditions are ideal, assuming you have 4 pairs and short distances, they could be used for Gigabit Ethernet.
  • Category 6- Previously compatible with the 5e, this new cable is governed by stricter standards and improved protection. It was designed as the standard for Gigabit Ethernet, so it is advised against 5 and 5e. In this case, it provides native speeds of up to 1000 Mbit / s or 1 Gbit / s with a frequency of 250 Mhz. If the maximum distance of this cable, which is 100 meters, is reduced to about 50, it could be used for Gigabit-10. There is also Category 6a which doubles the frequency to 500Mhz and reduces noise interference with foil-based protection to improve in Gigabit-10 Ethernet mode.
  • Category 7: it has been improved to get up to 600 Mhz (they have been improved to 1000Mhz) to work optimally in Gigabit 40/100. Similar to category 6a protections, but with individual protection for each of the four twisted pairs. In the case of 1Ghz operating frequency, it also makes it suitable for low-frequency cable television transmission.

Of course, add at the end that you can find both male and female connections in the market. They are very cheap and not complicated to obtain for your projects. The same for cables, plus you will have quite a few extras for them, such as converters from one type to another, etc., which are always good for certain applications ...

RJ45 checks

RJ45 checker

In specialized stores you will also find testers, devices that allow you to perform tests to verify the operation of your network cables, whether they are used or new that you have assembled yourself. There are also kits to work with network cabling that include the crimper, tester, inserter, etc. in the case.

However, there are many ways to check RJ45 connectors, as well as using a multimeter or multitester, testing it through a concentrator, etc. Here are some examples:

  • With a hub or concentrator- Connect only one end of the cable to a powered hub. If the LED corresponding to the port where we have connected the end lights up, it means that it works. Otherwise it would mean that it is not right or you have not connected it properly. You can also connect the other end to another device and try to make transfers to fully verify if it works ...
  • With a multitester or multimeter: You can use the tips of one of these devices to check if current is being transmitted through the cables.


Double RJ45 wall rose

Before I said that there are also female and male connectors, well, in general, for electronics projects, the most common thing is that you need a female connector to connect the ends of the male RJ45 cable. But you may also need to build or connect a rosette to leave the connection fixed or to connect your project to a building wiring network, etc.

By the way, for those who do not know, the rosette is that little plastic box that is usually found in buildings next to the telephone where the router / modem is usually connected, etc. In the market you will find several types, both simple with a single connection port, as double, to be embedded in the wall or external, etc.

Remember that the rosettes have a mechanism inside similar to that of an RJ45 to connect the cables. It can be one of the cables that you have chosen for your project, and basically what you have to do is open the rosette and connect it. If it is a recessed rosette in the wall, they usually have a trim that you must remove with a little lever and it will come out easy to let you see inside. If external, the protective case may be closed by snap clips or screws.

Once the lid is removed, you can strip the wires with the crimper to leave at least a few millimeters of its ends without the insulating protection, with the copper exposed. Remember that the untwisting of the pairs should not be more than 13 mm. It should only be just enough to allow you to work properly with the 8 threads, but without leaving them too unprotected.


Once you have the cables ready, the connection is similar to that of the RJ45, that is, you pass the cables through the slots for then leave them set with the inserter. It is better to pass them from the inside to the outside to prevent them from going out more frequently. The trickiest thing here is to prevent other cables already inserted from coming out while we are inserting the rest… But don't worry, it may cost you more at first, but then it's easy. Also, remember to respect the colors.

The way to use the inserter is easy, it is simply to use it with the end of the thread to fit it into the slots of the connector. When you push it, you will hear a crack, a sound that tells you that it is ready. Remember she squeezes the bare wire against the groove to crimp it and also cuts the excess.

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  1.   victorhck said

    Very complete and extensive article!
    There are also network cable meters, which detect cuts in the cables, meters of cable in case it could be a problem when communicating two points, and more checks ...


    1.    Isaac said

      Hola Victor,
      Thank you. I also appreciate your input on the meters.
      A greeting!