What’s the difference between T568A and T568B and why are there two wiring schemes?

Do copper cable have to be connected according to T568A or T568B? And why do the standards specify two wiring schemes? Read on to find the answer.

Answer: Both wiring schemes are recognized by the standards and both are used in the field. They differ only in the pin/pair assingment of the orange and the green wire pair. This makes no difference in signal transmission as long as a cable is terminated on both ends according to the same wiring scheme, i.e. on both ends according to T568A or on both ends according to T568B.

T568A was originally developed for a military project in the US, T568B was added later for civil applications. Neither wiring scheme has any advantages over the other. Many years ago there were cabling components that offered slightly better transmission values when being connected according to T568B, but those days are long gone.

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.