Cat5 RJ-45

jonny1982

Member
Location
CA
So I got into a frustrating argument today about the termination's of CAT5 cable to RJ-45's. An individual said as long as each end is exactly the same, it will work just fine. In my experience, that is definitely not true. In my experience, I just did both ends the same and internet connection was off and on. So I changed it and followed the A or B sequence and it worked perfectly. Don't you have to follow the 1-2, 3-6, 4-5, 7-8 pair sequence when connecting the ends because of the way the wires are twisted together? Am I crazy, or is this not absolutely the case. The reason it was frustrating was because the individual has been doing this job for many years and acted as if I was crazy for suggesting this. He even laughed and said "signals are color blind, they don't know what color the wires are!" Give me a break, it's because of the way the wires are twisted, isn't it? Please help and if someone can cite some reliable source explaining, that would be great.

Thanks!
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
With gigabit speeds you do need to make sure a data pair signal is on a physical twisted pair in the cable. I think what some people mean when they say it "doesnt matter as long as both ends are the same" is when following the 568A or B wiring styles.
 

jonny1982

Member
Location
CA
With gigabit speeds you do need to make sure a data pair signal is on a physical twisted pair in the cable. I think what some people mean when they say it "doesnt matter as long as both ends are the same" is when following the 568A or B wiring styles.

No, in this instance, he for sure meant that A or B didn't matter, as long as both ends where color coded the same.

Any documentation to show?

Thanks
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I don't see how it makes a difference. The difference between the two standards is that the location of pairs 2 and 3 are reversed. Those two pairs are the pairs used for ethernet data. How can the colors of the wires make any difference as that is really the only change?
On 568A, pair 2, (orange) is on pins 1 and 2 and pair 3 (green) is on pins 3 and 6.
With 568B, pair 3, (green) is on pins 1 and 2, and pair 2, (orange) is one pins 3 and 6.
 

Todd0x1

Senior Member
Location
CA
Your friend is wrong, here's why it does matter:

Ethernet uses twisted pairs with differential signalling. 100 base T uses two pairs, gigabit uses all 4 pairs, stuff with PoE of either speed uses all 4 pairs.

Each signal uses a twisted pair. One wire of that pair has the signal (+) and the complementary signal (-) is on the other wire. It is imperative that both components to the signal exist within the same twisted pair. If they are not, the condition is called a split pair and is the source of untold misery. The link will show connected, but performance will suffer due to the errors generated.

In theory you could switch colors around so long as you keep the positions of twisted pairs the same, but in practice just follow the A or B color codes.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I agree that the colors don't matter as long as each pair is wired as pairs.

You could use the brown/white pair on 1&2 and the blue/white pair on 3&6 if you wanted.

A crossover cable is the only kind you would intentionally mix end pairs.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Does it matters that each pair has a different number of twists per inch or does that just keep them from aligning with another pair?
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
He even laughed and said "signals are color blind, they don't know what color the wires are!"

But they do know what other wire they are twisted with.

These are the bozos who give us a bad name. Either learn what the color code is for 568A and 568B or don't do it at all.

And, you should know that I forbid field installing RJ-45 plugs.

-Hal
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Does it matters that each pair has a different number of twists per inch or does that just keep them from aligning with another pair?
What he ^^ said above: to minimize pair-to-pair cross-talk.

The purpose of twisting is to assure that both conductors will pick up any nearby interference (common mode), so the receiving end (differential amplifier - common-mode noise rejection) can ignore it, and pass only the difference signals. The greater the number of twists per inch, the higher the frequency (shorter wavelength) both conductors will pick up equally.
 

jonny1982

Member
Location
CA
He's saying you could do Orange on pin 1, orange/white on pin 2, blue on pin 3, blue/white on pin 4, green on pin 5, green/white on pin 6, brown on pin 7, and brown with white on 8 and as long as the other end is exactly the same, will be fine
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
He's saying you could do Orange on pin 1, orange/white on pin 2,
Correct.
blue on pin 3, blue/white on pin 4,
Not correct.
green on pin 5, green/white on pin 6,
Not correct.
brown on pin 7, and brown with white on 8
Correct.

Positions 3 and 6 must share a twisted pair, as well as 4 and 5.

This kind of wiring evolved from phone wiring, where positions 4 and 5 are line one, 3 and 6 are line two, and 1 and 2, and 7 and 8 were added later as additional lines.
 

Todd0x1

Senior Member
Location
CA
But they do know what other wire they are twisted with.

These are the bozos who give us a bad name. Either learn what the color code is for 568A and 568B or don't do it at all.

And, you should know that I forbid field installing RJ-45 plugs.

-Hal

Sometimes you have to field install RJ-45 plugs. I literally just got off a ladder installing cameras to come inside and cool off. Those need a field installed RJ45 plug inside the back box. Other end lands on a patch panel.

Properly installing RJ45 plugs is something one should know if theyre doing network wiring. Also need to know the difference between the types of terminals (2 pin straight = stranded wire only, 2 pin offset = solid wire only but not that good, 3 pin = solid or stranded and best on solid)
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Sometimes you have to field install RJ-45 plugs.

Jack on the end of the cable and a patch cord wherever possible though I admit sometimes that's not possible.

Properly installing RJ45 plugs is something one should know if theyre doing network wiring. Also need to know the difference between the types of terminals (2 pin straight = stranded wire only, 2 pin offset = solid wire only but not that good, 3 pin = solid or stranded and best on solid)

Aside from the wiring standard 568A and B, almost nobody knows that there are different plugs for solid and stranded wire . Use the wrong one and you are guaranteed to have intermittent problems. And stranded wire is for patch cords, not building wiring. Yeah, I know, you can get it real cheap on eBay. That's why.

So let's see, you have bozos who have no idea how to wire plugs then you have people who have no idea what plug to use. Yup. better off with a factory patch cord from a jack that any idiot should be able to install on the end of a cable.

-Hal
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
I’ve noticed the brown pair is not twisted as tight as the rest. I brought this up to a Leviton data wiring trainer, and he said it shouldn’t be, but I’ve noticed it on several brands.
 
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