What is a rj45 connector?

I think the vast majority of low-voltage practitioners have to admit one fact - That is the first thing they did was to learn what is a RJ45 connector and how to punch down rj45 connectors when they first enter the industry. Whether you are learning from a low-voltage master or in an integrated cabling class at university, the first lesson of the master or the teacher who teaches integrated cabling is about learning to punch down the rj45 connector. As you can see, although the rj45 connector is small though, it has a pivotal role in integrated cabling. For those who are involved in low-voltage engineering, Punching down rj45 connectors is the basic skill they need to master. 

Teaching in class

When it comes to RJ45 connectors, no one is unfamiliar with them. The ethernet connector is the plug mainly used for copper cabling systems. It is a standardized connector. It first appeared in the purchase of the Bell Communications System in the United States, began to be used in the 1970s to provide computer-aided telephone equipment authorized by the FCC, and was later accepted by the FCC and codified in the CFRs(Code of Federal Regulations). Its official name should be "registered jack".

The RJ45 connectors we use today is standardized. Its specifications in dimensions and structure have been fixed. This standard was first established by the Federal Communications Commission (FCC).

FCC

1 Catagories of RJ45 connectors.

The most common rj45 connectors on the market can be categorized into telephone connectors and ethernet connectors according to their functions; Also they can be categorized into 8P8C plugs (RJ45), 6P4C plugs (RJ11), 4P4C/4P2C plugs(RJ12) according to their structure; or being categorized into unshielded plugs and shielded plugs according to the presence or absence of a shielding layer; or being categorized into one-piece connectors, two-piece connectors, and multi-piece connectors according to the number of pieces; according to whether to need the punch down tools, they are categorized into connectors needs tools and toolless connectors. Let me introduce these connectors in the text below. 

RJ45 Connectors

1.1 RJ11 connector

Telephone connectors also called phone connectors, are mainly used for phonetic systems and have two main types: One is used for connecting telephone wires, telephone sets, or telephone switchboards, also called RJ11 plugs. since it has two specifications, 6P4C or 6P2C, so, is also called 6P4C plugs or 6P2C plugs.

                                     RJ11 connector

1.2 RJ12 connector

Another type of phone plug is mainly used to connect the telephone handset, FCC defines it as RJ 12 plug. Since its structure has 2 specifications - 4P4C or 4P2C, it's also called 4P4C/4P2C plugs. The size of this plug is relatively small. It is generally used to connect telephone handsets and telephone sets. The rise of mobile phones led to a sharp decline in the sales of telephone sets. As a result, the RJ12 plugs also gradually fade out of people's view. However, in the recent two years, especially after the boom of the Internet of Things (IoT). Some intelligent devices have started using RJ12 plugs as connectors for data transmission. As a result, the use amount of the RJ12 plug has also gradually risen in the past two years and returned to the public's view.

                                    RJ12 telephone connectors

1.3 Ethernet Connector

The ethernet connector is mainly used to connect the network interface of switches, routers, servers, gateways, wireless APs, computers, and other terminal equipment, as well as rj45 modules, rj45 patch panels, and other integrated cabling products. FCC defines it as RJ45. Its structure is 8P8C (8 positions, 8 contacts). The most common types are as follows: Cat5e connector, Cat6 connector, Cat6A connector, and Cat8 connector.

1.3.1  Cat5E RJ45 connector

Cat5E RJ45 connectors are used in the Cat5E cabling system. They are used on 3 occasions: 1 Used to assemble the finished patch cords, 2 Used to terminate with cable in monitoring and controlling projects, 3. Used for field termination to make patch cords in the low voltage project. For the standard Cat5E rj45 connector, the insert hole's aperture is 1.0mm, and terminated cable core wires are required to have a diameter between 0.85mm and 0.98mm. Its apertures are located side-by-side in the same horizontal line. Cat5E RJ45 connectors have two types: shielded and unshielded. Since the outer diameter of the Cat 5E cable is relatively small, the Cat5E shielded RJ45 connector is usually featured without a tail clip structure. Cat 5E ethernet connectors also have 2-piece, 3-piece, and even 4-piece designs. As the traditional Cat5E cabling products are mainly used in short links and 100-megabit networks, Therefore, the finished patch cords applied in this network environment generally use the traditional one-piece ethernet connector. However, in recent years, particularly after the introduction of the 2.5GBase-T and 5GBase-T protocol standards released by the 802.11 IEEE P802.3bz draft. Many manufacturers began to consciously use two-piece or even multi-piece ethernet connectors to make finished patch cords to increase the anti-interference ability of the cable.

                       Cat5E Ethernet Connector

1.3.2  Cat 6 rj45 connectors

Cat 6 rj45 connectors are mainly used for Cat 6 cabling systems. Its application is the same as the Cat 5E cable. It has an aperture of 1.1mm and requires that the inner core diameter of the cable terminated ranges from 0.95mm to 1.08mm. Its inserting holes are crosswise arranged up and down. And, the Cat6 rj45 connector is a little shorter than the Cat5 rj45 connector. The rj45 connectors used to assemble the finished Cat6 patch cords are generally three-piece designs. This type of ethernet connector has 2 splitting slots. One is used to separate and isolate 4 twisted pairs with the same role as the cross skeleton in the Cat6 cable. The other split slot is used to separate the 8 core wires and arrange them up and down, further reducing the cross interference inside the cable. Cat6 ethernet connector also has types: unshielded ethernet connectors and shielded ethernet connectors.

                                 Cat6 UTP ethernet connector

Category 6 shielded rj45 connectors come in two types. The first is a one-piece shielded rj45 connector. This type of rj45 connector can be seen as the combination of the original unshielded rj45 connector and a nickel/tin-plated copper shell as the shielding layer. This shielded ethernet connector has a "latch" inside to compress and fixed the cable, preventing the cable from falling out. The second type is the two-piece ethernet connector. The two-piece shielded ethernet connector has a nickel/tin-plated copper shell as the shielding layer, with a separate splitting slot, which is used to expand the gap spacing of the eight core wires of the cable. 2-piece ethernet plugs have better anti-interference abilities than one-piece ethernet plugs. The two-piece ethernet plug is designed with a tail clip structure. Its tail clip is used to lock the connecting cable to prevent the cable from falling off.

                           Cat6 Shielded rj45 connector

1.3.3   Cat 6A rj45 connectors

Category 6A rj45 connectors are used in 10 Gigabit networks. Cat6A rj45 connector is also divided into two types: unshielded and shielded. The structure of the Cat6A unshielded type is the same as the ones of Category 5 and Category 6 unshielded rj45 plug. The aperture of the Cat6A plug hole is 1.2mm, allowing cables of 1.05-1.18mm to be terminated with it. There are two types of shielded rj45 plugs for Cat6A. The first is a two-piece shielded rj45 plug that requires the use of a crimping tool. The structure of this type of rj45 plug is the same as the Cat6 two-piece shielded rj45 plug we mentioned above. The second type is the toolless shielded rj45 plug. This type of rj45 plug refers to the termination mechanism of the toolless module. The operator needs to arrange, align and cut the eight core wires of the cable to a length that can be directly inserted into the rj45 plug. Then insert the core wires one by one in accordance with the color code on the label strip, and finally close the outer toggle.

   Cat6A Shielded rj45 connector

1.3.4  Category 8 rj45 connector

Category 8 rj45 connectors are used for 40Gbps networks. Category 8 rj45 connectors are all shielded types. There are no unshielded types. The structure and type of Category 8 shielded rj45 plugs are basically the same as the Category 6A shielded rj45 plug. Category 8 RJ45 plugs will be more likely to be the toolless type. Because to improve the anti-interference ability. The shielding layer of Category 8 rj45 plugs is always made thicker. Add to it that the out jacket of core wires itself is usually thicker, there is much possibility that the cable cannot pass the fluke testing. Therefore, will use tool-free mechanisms to solve the problems.

Cat8 toolless rj45 connectors

1.3.5  Category 7 rj45 connectors

You can find that I did not mention the category 7 rj45 connectors in the above text. This is because Category 7 rj45 connectors are not the common RJ45 connector types such as Category 5E and Category 6. And category 7 connectors defined by ISO are not backward compatible. People use less. Therefore, we will not write about it here. In addition, I must clarify that the category 7 rj45 plugs that you buy on some e-commerce sites should not be genuine.

Cat7 connectors

1.3.6   Pass-through rj45 connector

In addition, a pass-through rj45 connector has recently come out. This type of rj45 connector is characterized by the fact that the head of the rj45 plug is not closed, but open. The advantage of this rj45 plug is that there is no need to cut the wires in advance or to do cable pre-connection processing. The smooth wire will be terminated directly. Use the crimping pliers that have the cutting function to crimp and cut the wires. As this kind of rj45 plug is open, the copper conductor exposed to the air is very easy to oxidation thus the wire cable may have cover cracking, short circuit, packet loss, etc... And what's more, this pass-through rj45 plug can only be compressed by crimping pliers with both crimping and wire cutting function. The operators have to purchase an additional set of tools. This will increase the cost of construction. Therefore, it is not recommended to use the pass-through rj45 plugs on a large scale.

  Pass-through rj45 connectors

2 Structural composition of rj45 connectors

The rj45 connector consists of two parts. One is a transparent plastic shell and the other is a metal insert (often referred to as a "gold pinout"). The material requirements of the rj45 connectors are based on these two structures.

2.1  PC plastic shell

The plastic housing of the rj45 connector is made of PC plastic, the scientific name of PC is polycarbonate. It is a linear polyester carbonate. It is transparent and colorless, heat resistant, and has good impact resistance. At room temperature, its mechanical performance is excellent. And with no need of adding any flame retardant, its flame retardant grade has reached the 94V-2 level defined by UL.

 PC plastic

PC plastic is not all colorless and transparent but also has a light blue transparent color. The picture shows Bayer's PC plastic. Because Bayer uses a unique formulation. Therefore, the appearance of Bayer PC plastic is not the same as other manufacturers. Although the appearance is different, the performance of Bayer PC plastic is not too different from the performance of common PC plastic. Therefore, the light blue rj45 connectors that you see in the market can also be used as normal.

At present, the main foreign PC plastic manufacturers are Bayer Group of Germany, Teijin of Japan, and LG of Korea. The main domestic ones are Sinopec, PetroChina, and so on. The foreign PC plastic will be a little better than the domestic ones in quality.

2.2. How to judge the quality of rj45 connectors

In the daily construction of low-voltage projects, we will often use the modular plug. A good quality modular plug is very important for our construction and later maintenance. We can initially judge the quality of the rj45 connector by the out shell.

First of all, after we open a box of rj45 connectors, we can shake the whole package a few times. If the sound of shaking is very crisp, it shows that this connector's shell is made of PC plastic whose purity and density are relatively high. Because the polymer material of high purity and density has a relatively better acoustical conductivity. Therefore, the sound is crisp and clear.

Secondly, we can pick up an rj45 connector to observe its appearance. The high-quality connector's plastic shell is pure transparent or light blue transparent. You can not find impurities, black spots, white spots, and things like that. This is a key point to judge the quality. While the poor-quality connector's shell is more turbid. At the first glance, you can see the difference in texture.

Another way to judge quality is to bend the shrapnel. It's well-known that for some of the poor quality connectors on the market, we dare not touch its shrapnel during installation. Once touched, it is broken. The good quality rj45 connectors are not like this. For a good quality rj45 connector, we can directly fold down the shrapnel 180° and then fold it back. the slow folding of more than 15 times will not cause a break.

2.3  Metal insert.

In addition to the plastic shell, every rj45 connector has a metal insert. This metal insert is usually called pinouts and also called "gold pinouts". This insert is generally made of bronze or phosphor bronze. Bronze or phosphor bronze is used because these two materials have good mechanical properties and high hardness, and both of them are wear-resistant, it is easy for them to pierce the plastic jacket of the core wires of the ethernet cable and contact copper conductor of the cable, so as to achieve the purpose of communication.

 Ethernet connector inserts

Some rj45 connector brands on the market advertise that their metal insert material is pure copper or oxygen-free copper. This is a mislabeling. Because, as we mentioned above, the rj45 connector insert is used to pierce the out jackets of the core wires inside the LAN cable. Pure copper and oxygen-free copper are soft and cannot pierce the out jackets of the core wires. Therefore, the rj45 connector's insert is bronze or phosphor bronze, not oxygen-free copper and pure copper.

As the alloy of copper and copper is very easy to rust. If the rj45 connector's inserts are not plated, the inserts will turn green or black, which is the rusting phenomenon of the ethernet connector. Once the ethernet connector's contact is rusted, it will lead to an error and an offline phenomenon.

Therefore, we have to carry out an anti-oxidation plating treatment on the rj45 connector insert. That is what we often called the nickel plating process. Nickel is an active metal that can be easily oxidized. However, after its surface is oxidized, it generates a dense oxide film that prevents further oxidation of the inner material. Therefore, after nickel plating, the insert will not rust. From the observation of the side of the inserts, we can know whether the nickel plating process is finished or not. If it is nickel plated, the side is silvery white. Otherwise, the side is yellow.

In addition, we can see that the outer end surface of the ethernet connector's insert is golden yellow. This is the result of gold plating. The gold plating on the surface of the ethernet connector is to make the connectors more wearable and reduces the resistance of the contact points. This is very important when it comes to POE power supply.

Therefore, you can judge the quality of the rj45 connector which you are using every day according to the above-mentioned characteristics.

3, How to terminate the rj45 connectors onto the ethernet cable

3.1, The structure of the network cable

The network cable is also called a twisted pair cable, the reason why it is called twisted pair is that it consists of eight copper wires, each of which is a different color, where every two copper wires are twisted together, so there are four twisted pairs of copper wires.

The colors are, respectively, orange white, orange, green white, green, blue white, blue, brown white, brown, where orange white and orange entwined together, green white and green entwined together, and so on, forming four pairs of twisted pairs.

  Structure of the ethernet cable

 3.2, The wiring sequence of the network cable

The eight copper wires inside the network cable must be placed in order, if the order of wires is not correct, the network cable cannot be used in the network connection. So in the rj45 connector's termination, knowing its wiring sequence is essential.

     Wiring sequence of 568A and 568B

There are two types of network cable connections, one is a straight-through wired cable(T568B), and the other is a crossover wired cable(T568A).

Straight-through wired cable: generally used to connect different devices, such as computers connecting to the router, and the router connecting to the switch, it is the most common way of an ethernet connection, both ends of the network cable need to use the same wiring sequence.

Crossover wired cable: it is also called reversal cable. It is a connection method used to connect the same type of device, such as two computers directly connecting to each other. If you use a straight-through cable to connect two computers directly without passing through a router or switch, these two computers cannot communicate.

In China, there are generally two types of wired cable sequences: T568A and T568B.

Standard T568A wiring sequence: 1-Green White, 2-Green, 3-Orange White, 4-Blue, 5-Blue White, 6-Orange, 7-Brown White, 8-Brown.

Standard T568B wiring sequence:  1-Orange white, 2-Orange, 3-Green white, 4-Blue, 5-Blue white, 6-Green, 7-Brown white, 8-Brown.

Straight-through wired cable:  Both terminal ends comply with the standard T568B wiring sequence, both two ends are the same wire sequence and one-to-one correspondence.

Crossover wired cable:  One end complies with the T568A standard, and one end complies with the T568B standard.

I wonder if you have found, The difference between T568A and T568B is that 1 and 3 switched, and 2 and 6 of the wire sequence switched. In other words, the crossover wired cable has only four different wire sequences from the straight-through wired cable. They are opposite to each other.

This is because, although there are four twisted pairs and eight copper wires, in fact only four of them are used in the network, namely the 1, 2, and 3, 6 pinouts in the ethernet connector,  they are playing the role of receiving and sending signals.

Since the crossover wired cable is used to connect devices of the same type, one end of the sending signal needs to be connected to the other end of the receiving signal, so the wiring sequence of the two ends is reversed.

3.3, The required tools.

After you understand the structure of the ethernet cable and wiring sequence, you also need to have a very important tool, this tool is called crimping pliers.

This tool is very important, if you do not have this tool, it is impossible to terminate the rj45 connector onto the ethernet cable, do not try to use tools such as screwdrivers to crimp the rj45 connector, any other tools are prone to the damage of ethernet connectors.

This tool is not expensive, only costs a dozen dollars, this tool along with screwdrivers, scissors are all the necessary tools for home life, if you are a person who likes DIY, it is recommended to get one plier!

  Impact the ethernet plug with a crimping plier

3.4, The termination steps

The next is the most important part, after the theory teaching, it is time to practice, there are 7 steps as follows.

3.4.1, Based on the need to confirm whether the ethernet cable you are going to make is a straight-through wired cable or crossover wired cable, the general household use is a straight-through wired cable.

3.4.2, Peel the outer jacket of the ethernet cable as long as 3cm from the terminal ends with pliers, remember not to strip the jacket of the inner eight copper wires. Split the 4 twisted pairs, and arrange them in the correct sequence.

3.4.3, Put the arranged core wires in the cutter position, cut the wires in an aligned way and keep the remaining wires 1.5cm long.

3.4.4, Then insert the eight small copper wires into the slot of the ethernet connector and push all core wires to the end.

3.4.5, Put the rj45 connector into the hole of the crimping plier, and press it with the crimping plier, the crimping pliers can pierce the outer jacket of the 8 copper wires so that the wires' conductor can touch the ethernet connector's pinouts, and you can pull out the plug until hearing a crisp noise.

3.4.6, Until now, one end of the cable has been terminated onto the rj45 connector. Using the same method, you can terminate the other end of the cable.

3.4.7, After both ends of the cable, are terminated, the patch cord should be tested with a Fluke tester. If all lights are on in turn, it means that the cable termination is successful, if there is no cable tester nearby, you can plug the network cable directly into the rj45 port of the computer to test whether the computer can access the internet, normally internet access means that the cable termination is successful.

  cable tester