The Difference Between the T568A and
T568B Wiring Standards Last updated: 6/20/2001
Q. What is the difference between the ANSI/TIA/EIA
T568A and T568B color code wiring standards?
A. T568A and T568B are the two color
codes used for wiring eight-position RJ45 modular plugs. Both are
allowed under the ANSI/TIA/EIA wiring standards. The only difference
between the two color codes is that the orange and green pairs are
interchanged. T568A wiring pattern is recognized as the
preferred wiring pattern for this standard because it provides backward
compatibility to both one pair and two pair USOC wiring schemes. The
T568B standard matches the older ATA&T 258A color code and is/was(?) the
most widely used wiring scheme. It is also permitted by the ANSI/TIA/EIA
standard, but it provides only a single pair backward compatibility to the
USOC wiring scheme. The U.S. Government requires the use of the
preferred T568A standard for wiring done under federal contracts. The
following diagrams look at the jacks from the front.
The wiring at the rear of
the jack varies by manufacturer and may not be in the same sequence as the
front. However, compliance with the color codes is maintained by
routing the connections at the back to the proper sequence at the front of
the jack. That is usually done by a small printed-circuit board in the
jack assembly. CAT 5e jacks (right) may have a twist inside the jack
to reduce crosstalk.