It is well known that there are various kinds of connectors used to terminate the fiber optic patch cables, such as LC, SC, FC and MTP/MPO connector. As for terminating the copper based patch cables widely applied in home wired network, there are also several RJ-style connectors published like RJ11, RJ12, RJ21, RJ35 and RJ45 jack, etc. Among these jacks, the RJ11 and RJ45 jack are the most commonly used jacks that have common in appearance, which may be not easy to tell. Since the RJ45 jack is specially designed for terminating the Ethernet patch cable like Cat 5e cable and Cat 6 cable, do you wonder that can the Cat 5e cable or Cat 6 cable be also terminated by RJ11 jack? Let’s study the RJ11 and RJ45 jack information and find the differences of these two jacks, then seek the answer.

What are RJ11 and RJ45 Jack?

“RJ” is the acronym of “registered jack”, which is a standardized telecommunication network interface designed to connect voice and data equipment to a service provided by a local exchange carrier or long distance carrier, first published by the Bell system and managed by the Federal Communication Commission(FCC). As for the number 11 and 45, they stand for different types of the registered jacks for easier and better identification.

RJ11 jack, sometimes a 6P2C (6-position, 2-conductor) connector but mostly a 6P4C connector, is specially applied for telephone lines, while RJ45 jack is a 8P8C modular connector used for terminating twisted-pair cables in Ethernet network. In a typical 6P4C RJ11 jack, only four out of the six positions are generally used to terminate phone lines and the rest two are idle, but the eight positions in the RJ45 jack will be taken fully use of, four for sending and receiving data and the other four for other technologies or power networking devices, as shown in the following figure. If you want to use these two types of jacks to terminate the telephone line or the Ethernet cable, please do it in accordance with the instructions for correct terminations. Besides, it should be noted that the Ethernet cables like Cat 5e cable and Cat 6 cable can be also referred to as RJ45 cables since they can be terminated by the RJ45 jacks.

What are the Differences Between RJ11 and RJ45 Jack?

Although the RJ11 and RJ45 Jack seems very similar in appearance, but they do differ from each other in the structure. Firstly, it is obvious that there are differences in their internal structures. If you check the jacks which are connected with wires, you’ll find that there are four wires in the RJ11 jack but eight wires in the RJ45 Jack. As a result, the RJ45 Jack is generally bigger than RJ11 jack. Secondly, an typical RJ11 jack has six pins but only four of the pins in the middle are participated to connect the four wires, while there are eight pins in an RJ45 jack and both of them are used for cable termination.

Meanwhile, these two jacks have different wiring schemes, which you can learn from the figure below. As for the wiring scheme of the RJ11 jack, you can take the POTS (plain old telephone lines) residential telephone wiring as a typical example that generally contains two pairs of wires, which are designed for two separate telephone lines. And the center pins (red and green) contain the first telephone line, while the black and yellow pins contain the second one. As for the RJ45 jack, there are two wiring schemes, T-568A and T-568B, each of which can be applied in making cross-over cable or straight-through cable. A cross-over cable is terminated with an RJ45 jack used T-568A wiring scheme in one end of the cable and another RJ45 jack used T-568B wiring scheme in the other end, while the straight-through cable is terminated with two RJ45 jacks with the same wiring scheme, T-568A or T-568B.

Moreover, the biggest difference between these two jacks is their application. As for the RJ11 jack, it is the cable connector that is used in telephone sets, ADSL, and modem cables, etc. However, the RJ45 jack is designed with the aim of terminating Ethernet patch cable in networking, where you connect computers or other network elements to each other.

Can Cat 5e or Cat 6 Cable Be Terminated with the RJ11 Jack?

After knowing the basic information of the RJ11 and RJ45 jack and analyzing the differences between these two kinds of jacks, it is simple and clear that neither Cat 5e cable nor Cat 6 cable can be terminated with the RJ11 jack. Why? As mentioned above, the RJ11 jack is smaller than RJ45 jack and there are only six pins to terminate the wires in the Cat 5e cable or Cat 6 cable. Therefore, if we use the RJ11 jack to terminate the Ethernet patch cable that generally has eight wires, there will be two wires that can’t be terminated and work normally. What’s more, these two kinds of jacks are designed for different applications. As the RJ11 jack is used for terminating telephone line and RJ45 jack is to terminate Ethernet patch cable in networking, only choosing the proper jack can the performance of the telephone line or the Ethernet patch cable can be ensured.