What Does a Bad Termination Look Like?
Written by Don Schultz, Technical Sales Representative and Fluke Networks Certified Technician
Got ya! You came into this article thinking we were going to talk about unfair firings. Nope. In this article, we are talking about thoroughly jacked-up RJ45 and keystone jack terminations. The content that follows may be shocking. Most people will find it quite humorous. Viewer discretion is not advised. You have to see this!
What makes an Ethernet cable termination bad?
- Excessive untwist of the twisted pair conductors
- Crossed wires
- Nicked conductors
- Bad electrical contact
Some of these mistakes show up as a cable that simply will not work. Others show up in insidious ways like slow speeds and intermittent connectivity.
First up, we will showcase terminations that straight up won’t work at all:
Um. I just don’t have words… Somebody does not know about untwist.
The above photos are extreme examples of excessive untwist. What is that and why are the wires twisted anyway? Well, read up on Why Are Wires Twisted Inside an Ethernet Cable? for more information.
Suffice it to say the more you untwist those pairs, the less performance you get. There is a maximum amount of untwist you can go before problems happen, and that is 0.50 inch. That means the maximum you can untwist that pair is 0.50 inch from the last twist in the pair to where the wire makes actual electrical contact.
Not all problems are so extreme. Here is an example of a conductor pair that is barely out of spec:
Check out the green pair. Other pairs cut away for clarity.
For RJ45 connector plugs, here is a great example of excessive untwist that otherwise appears to be good until you take a closer look:
Close, but not quite there. It might work, but not at full speed!
Sometimes seeing bad next to good is a great way to get the idea:
The top one is bad. Middle is just in specification. Bottom is the best you can do.
So, how does the bad RJ45 termination manifest itself? Usually, you will get a 100 Mb/s connection instead of the 1,000 Mb/s connection (1 Gigabit) you were expecting. The connection will work, but only barely.
The next malady is crossed wires. This happens to the best of us, including me. It pays to double and triple check your terminations for the correct color sequence. Related to this is whether you are using T568A or T568B. I will typically terminate using the T568B sequence, but there is nothing wrong with using the T568A sequence either. Just pick one and stick to it, for more see, T568a vs T568b, Which to use.
Illustrated here is not an issue between the two sequences, but a conductor out of place regardless of which sequence you use.
Can you spot what I did wrong? Here are the conductor sequences for this particular keystone jack.
Based on the two pictures above, you can see I miss-punched the brown pair. How does this happen? Simply not paying attention or going too fast, so no excuses for me. This can also happen when you are working with different brands of keystone jacks. Not all keystone jacks are wired the same way!
Crossed wires inside of an RJ45 plug are much more challenging to spot. This is easily a big argument for the superiority of pass through connectors. The advantage to the pass through style is that you can confirm the color sequence prior to crimping it down.
Here are two examples of crossed wires:
Oops! The orange pair is crossed. Not easy to spot until you look close.
A crossed wire in a plug is often the result of using standard push-in style RJ45 plugs. With these types of plugs, you “guess and cut” and then insert. During the insertion process, one wire will cross over and end up in the wrong spot.
Upside down terminations can occur with any plug. The color sequence looks correct because they are lined up properly, but in reverse. This makes it very easy to overlook. I did this recently and ended up killing an expensive PoE surveillance camera. The type of PoE being used was passive (always on) PoE, and the camera did not have a chance. Kaboom!
Nicked conductors happen when your cable stripping tool not only slices through the cable jacket but also the conductor insulation. The only way to spot this is to check your cable strips before termination. If you see a slice in the insulation or a glint of copper, you need to readjust your strip tool and start again.
See the slice in the solid orange conductor, right at the cable jacket edge?
Depending upon the severity of the nicked conductors, this damage will manifest itself in one of two ways:
- Poor cable performance
- Non-working cable
Considering there are several other factors that can cause those two issues, my sincere advice is to check those conductors rather than spend hours spinning your wheels trying to track down what went wrong! Nicked conductors are exceedingly difficult to track down.
Bad Electrical Contact
It is exactly what it sounds like. This happens when a conductor is not fully punched down into the IDC slot of a keystone jack or a popped pin on an RJ45 plug. When making your terminations, always check to be sure that no golden contacts are raised on RJ45 connectors, and your conductors are all the way to the bottom of the IDC channel in a keystone jack.
There you have it. The most common Ethernet termination maladies and how to spot them. Plenty of RJ45 plugs, cable, and keystone jacks were seriously harmed to bring this article to you :>)
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