What’s the difference between RJ45, RJ12 and RJ11 plugs?

Some RJ45 jacks also accept RJ12 and RJ11 plugs and some don’t. What’s the difference between the three plugs and what happens when the wrong one is plugged in?

Answer: The RJ45 plug is the well-known IT connector with eight contacts. The RJ12 looks similar but has only six contacts and is slimmer than the RJ45. The RJ11 has the same housing as the RJ12, but only four of the six contact positions are populated with contacts. When an RJ12 or RJ11 plug is plugged into an RJ45 jack the sides of the slim plugs might bend the outer contacts no. 1 and 8 of the RJ45 jack. When this happens, the jack cannot be used for data transmission anymore.

Telegärtner’s RJ45 jacks have an integrated protection against overbending the contacts. Even after RJ12 and RJ11 plugs were plugged in several times, all of the jack’s contacts are still working which gives users the peace of mind that their cabling infrastructure works reliably which protects the investments made.

Nobody knows everything. A comprehensive topic like IT cabling inevitably raises questions. This column gives answers to questions which reached Telegärtner’s Technical Helpdesk and which we consider interesting for everyone. Please do not hesitate to send us your questions, we will be happy to answer them. The questions will be published anonymously, of course.