Terminating Pass-Through RJ45 Connectors onto Solid Copper Ethernet Cable  --  A Really Bad Idea?

Terminating Pass-Through RJ45 Connectors onto Solid Copper Ethernet Cable  --  A Really Bad Idea?

Written by Don Schultz, trueCABLE Senior Technical Advisor, Fluke Networks Copper/Fiber CCTT, BICSI INST1, INSTC, INSTF Certified

A question that keeps coming up is “Do pass-through RJ45 connector plugs not work as well as the standard solid nosed kind?” We also get asked if pass-through RJ45 connectors pose any additional particular troubles with power over Ethernet (PoE). Typically, the question is followed by real life or anecdotal information about others who have had trouble with non-working or even damaged network devices. As it turns out, there is typically a kernel of truth in any urban legend or rumor. The answer is far more complex than you might expect (isn’t it always?) and involves a discussion that goes far beyond just the pass-through style RJ45 8P8C connector plug. We will parse through what the real issues are, and why they have shaped up this way to become such a persistent source of anxiety for newbies as well as experienced installers. Finally, we will explain (all in one place) what the challenges are around terminating these annoying pieces of plastic onto Ethernet cable and define some best practices not only borne of my experience but also rather extensive BICSI and Fluke Networks training.


In other words, buckle up because we are about to get deep in this and really flush out the truth.


A Teeny Bit of History

 Solid nosed standard RJ45 8P8C terminated

Solid nosed standard RJ45 8P8C terminated

Solid nosed (otherwise called “standard”) 8P8C RJ45 Ethernet plugs have been around since 1995, designed for the original Cat5 Ethernet cable that ran at 100Mb/s (long since deprecated and replaced by Cat5e). Ethernet wiring became more and more pervasive in the ensuing years. Manufacturers like Apple, HP, IBM, and more came up with affordable desktop computers. Top this off with the desire to network computers together to share files more easily (and the invention of the Internet) and now everyone was looking to get in the Ethernet game. For most people, buying a simple pre-terminated and factory made Ethernet patch cable worked great. You plug one end into your PC and other end into your switch/router and off you go. However, not all installations are so simple and quite a few installers complained about the “guess, cut, fit, retry” method often associated with putting on 8P8C plugs. This style of RJ45 8P8C plug takes time, experience, and patience to work with. They are still sold today!

Pass through RJ45 plug

Guessing and estimating that cut! Ugh.

Pass-through RJ45 8P8C plugs have been around for about 15 years. These devices are relatively new to the scene. The intent of this style of modular plug was to:

  • Make installation faster
  • Reduce termination mistakes (crossed conductors, etc.)
  • Reduce scrap
  • Greatly reduce frustration!

Pass-through RJ45 8P8C plug in process of termination.

Pass-through RJ45 8P8C plug in process of termination. Note the exposed copper at the end of the conductors. The copper was stretched during the conductor straightening process. That’s another problem we will talk about later.

As the newer passthrough style of RJ45 8P8C plugs caught on as the easier to use option, this allowed entry to an entire new class of installers: DIY or Do It Yourself types that would not have otherwise attempted to install Ethernet cable in the first place. I like to call them (and this includes me about 10 years ago) “Weekend Warriors”. This led to many (as in a LOT) of various manufacturers getting involved in making this type of termination resulting in a great deal of variety.

However, there is no “free lunch”. While passthrough 8P8C Ethernet RJ45 plugs are easier to install onto your Category 6 cable, they had to be made user friendly in order to accomplish this. That’s where the trouble can (and does) start. With greater variety comes the possibility of compatibility issues. To make matters worse, not all RJ45 8P8C plugs are equal by design, not all manufacturers are equal in quality, and even the very Ethernet cable you wish to terminate is not necessarily equal either.

So, did pass-through RJ45 modular connectors solve the woes they were intended to solve? Well, sort of. The original problems of ease of use were indeed solved to the maximum extent possible, all things being equal. However, not all things are equal and a pass-through RJ45 is still an RJ45 and if taken in the context of asking “Did pass-through RJ45s make the world a better and more perfect place?” I would say…nope. Quite frankly, I will characterize the idea as well intentioned but ultimately the wrong answer to something that should never have been an issue. Why is that and does this kind of connector pose any special danger for PoE devices? Read on, but grab a cup of coffee.

The Least Correct Answer to the Wrong Question

“How can this be solved so RJ45 pass-through 8P8C modular connectors are 100% reliable?”, you may ask. The short answer is you cannot. The better question is it even possible to make RJ45 8P8C terminations in the field that are 100% reliable? Offering pass-through style over the standard style only made it easier to do an unwise activity faster. Ultimately, what we have is an attempt to correct a problem that has a better answer if you know where to look. The real question is “Should I be trying to put on RJ45 8P8C connectors at all?” Now, we are getting somewhere.

The root problem is not pass-through RJ45 connectors plugs. The root problem is you are not supposed to terminate RJ45 8P8C plugs by hand onto bulk cable unless presented with no other choice, especially when it comes to solid copper Ethernet cable.

IDC or Insulation Displacement Contact terminations that are found in keystone jacks, patch panels, and field termination plugs are far superior for mechanical (and therefore electrical) stability. RJ45 8P8C modular connectors are actually supposed to be terminated onto stranded copper Ethernet cable at a factory by a machine.

IDC Terminations (Insulation Displacement Contact)

Tool-less keystone jack showing the IDC termination prongs

Tool-less keystone jack showing the IDC termination prongs

IDC termination

IDC termination. The prongs cut through the conductor insulation and then bite into the copper from right angles. This type of termination is EXCELLENT for mechanical/electrical stability. They don’t tend to shift under stress.

  • IDC terminations create an air-tight seal
  • IDC terminations pierce the insulated conductor from the sides preventing longitudinal shifting of the conductor wire under stress

RJ45 8P8C 3 Prong Contact Pin Terminations

3-prong golden contact pins inside a RJ45 connector

3-prong golden contact pins inside a RJ45 connector

three prong contact pin

The three prong contact pin will pierce the insulation from along the side of the insulated conductor.  Longitudinal stability is not nearly as good as IDC terminations.

  • The termination strategy used for RJ45 8P8C connectors is susceptible to stress from conductor movement when the cable itself shifts at the rear of the RJ45 plug housing
  • The golden contact prongs do not create an air-tight seal
  • The golden contact prongs displace the insulation along the side of the copper conductor

Professional installers already know to use the “rack to jack” method for terminating bulk solid copper Ethernet cable meant for permanent installation. New installers assume that RJ45 8P8C plugs are the way to terminate any type of Ethernet cable because:

  • Most people have only seen patch cables in stores, which happen to be using stranded copper conductors and are factory terminated by machines capable of a level of precision that no human can achieve
  • New installers don’t necessarily have the experience or formal training to understand the best way of terminating Ethernet cable due to lack of access to costly professional training and standards documents like TIA 568
  • Newer installers may not fully understand what a keystone jack or patch panel are, what IDC terminations are, and what gets used where
  • There is a great deal of well intentioned but misleading (or even straight-up incorrect) information floating around on the Internet

Let’s face it, the topic of terminating Ethernet cable and networking in general can get complex and folks are looking for a quick and simple solution to their needs.  

A Perfect Storm

The accessibility of bulk solid copper Ethernet cable has been a boon to installers. It used to be bulk solid copper Ethernet was something that cost a lot, was a bit hard to find, and was used by only the most geeky people on Earth. Nowadays, take a look at Amazon or even your local hardware store and you see the market is literally flooded with various manufacturers making a dizzying variety of bulk Ethernet cable. Prices have come down drastically, and this is a good thing! Combine this boom with newer innovations in termination technology (tool-less keystone jacks and pass-through RJ45 Ethernet connectors) and more people are installing their own Ethernet cable, many without the benefit of formalized training. Adding to this, now a wide variety of people are installing PoE powered surveillance cameras, environmental controls, lighting, and WiFi APs (access points). Most new installers (and many older experienced ones) are opting for pass-through RJ45 connectors due to ease of use. Inevitably, as more people of various skill levels get into installations the number of problems seen in the field will increase. One item has been the source of persistent issues, however, and that is the seemingly ho-hum RJ45 8P8C plug.

The issues with terminating an Ethernet cable with a RJ45 8P8C plug in the field (by you) is multifold. Some issues can be mitigated and some cannot. Here are the obstacles you face and what you have control over:

What you can control to a certain degree:

issues with terminating an Ethernet cable with a RJ45 8P8C plug in the field

What you have less control over:

issues with terminating an Ethernet cable with a RJ45 8P8C plug in the field

Now, you might be scratching your head at this point.  Didn’t trueCABLE pull out all the stops to offer RJ45 8P8C plugs and Ethernet cable tested as a system in order to eliminate this problem now and forever?  Well, we certainly gave it a good shot and largely succeeded at it.  We also developed a few “puckered mouth” moments along the way in the process. 

Time for Some Frank and Earnest Talk

You might be asking yourself why anyone even sells separate RJ45 8P8C connectors considering all of the foregoing issues. Well, it comes down to two reasons:

  • Consumers demanded them, and therefore we now have a supply
  • Sometimes it is appropriate to field terminate 8P8C RJ45 modular plugs so there is a legitimate reason to use them from time to time and we will get to those scenarios

However, if you look at some very large manufacturers’ websites as of late, you might notice an interesting trend of less and less RJ45 8P8C modular plugs being offered. Manufacturers have backed off a bit, and through my own experience and rather extensive testing with a Fluke DSX-8000, so has trueCABLE. If you pay careful attention to our website you will notice a not so subtle shift towards strong recommendations for shielded and unshielded field termination plugs for high performance Cat6A and even thick Cat6 shielded Ethernet cable when a male plug end is required. I will tell you rather readily that RJ45 8P8C plugs terminated onto solid copper bulk Ethernet should be your last termination option and then only when something in your particular installation demands it.

How did trueCABLE come to this conclusion? Time for full disclosure! We have had a few issues reported in the field, too. Let’s explain why, despite our best efforts to make RJ45 8P8C plugs and solid copper Ethernet cable a reliable and tested system, 100% perfect fitment is not achievable:

Here is one half of the problem:

  • Insulated conductors (and you have eight of them inside Ethernet cable) have a nominal diameter and a stated tolerance range
  • Nominal diameters are the target diameters, but considering we are talking about coating copper wire with thin plastic that plastic can and does vary in thickness
  • The tolerance range is typically 0.05mm +/-
  • The copper thickness has a tolerance as well!
  • Variability from one production run to another can cause an Ethernet cable to be on the outside maximum +/- and still be in specification
  • The nominal diameter is what people use for fitment decisions because that is all you have to reference when making a decision

In short, soft plastic coatings are very difficult to hold to a certain specific diameter with a high degree of precision.

Here is the other half of the problem:

  • RJ45 8P8C plugs are hard plastic
  • RJ45 8P8C plugs have a strict compatibility (fitment) range for insulated conductors
  • The Ethernet cable you are working with might be at the upper or lower limits of its manufacturing variance, and that can put the insulated conductor out of the strict compatibility range of the plug

An example:

  • A certain pass-through RJ45 plug has a strict insulated conductor compatibility range of 0.95mm to 1.05mm
  • A certain Cat6 Ethernet cable has a stated nominal insulated conductor diameter of 0.97mm, but also a manufacturing tolerance range of 0.04mm +/-
  • Let’s say that particular lot of cable dropped to the minimum side of the range, and now has REAL insulated conductor diameters of one or more conductors that measure 0.93mm. Uh oh. Not good, because it just fell below the strict minimum by 0.02mm.
  • Will the plug and cable combination work? Perhaps, but more likely you will have issues that show up at higher speeds or if you are using PoE.

So, which is at fault? Is the cable defective or the plug defective? The answer is neither are defective. The cable is within specification but you were unlucky enough to get a spool that was on the low side of acceptable. Of course most people don’t fully understand the nuances here and will blame the cable, the plug, or their crimp tool (or all three). This leads to warranty claims (and we have a Forever Warranty we are serious about) and some people getting discouraged with their project. I don’t blame them, and I feel their frustration.

Has trueCABLE had this happen to us? Oh yes, a couple of times. In fact, we have had to make some quick changes to recommendations on our website and Amazon in order to compensate. trueCABLE pays close attention to customer feedback and can quickly pivot to make sure everyone stays happy. Of course we honored the Forever Warranty on any “edge case” issue where this issue has reared its ugly head.

No, trueCABLE will not stop selling RJ45 8P8C plugs! Despite the temptation to do just that, we have instead shifted our product recommendations, made some manufacturing changes, and now are actively educating our customers because your success is our success. This means I have some pretty strong and new recommendations going forward.

I strongly recommend you pay attention to this part!

  • Patch panels, keystone jacks, or field termination plugs are the preferred way to terminate solid copper Ethernet for maximum performance and reliability
  • DO NOT construct Ethernet patch cables (RJ45 to RJ45 plug) with solid copper Ethernet. In fact, buy factory pre-terminated patch cables that were assembled and tested before you bought it.
  • IF THERE IS NO OTHER CHOICE but to construct a short Ethernet patch cable in the field, this should be a permanent connection in a spot where it won’t be messed with. Second up in importance is to terminate both ends to field termination plugs! Finally, don’t plug and unplug this cable often because solid copper conductors don’t hold up to repeated handling.
  • There is precisely one scenario where it is acceptable to terminate RJ45 8P8C plug onto solid copper Ethernet cable and that is where the end point device won’t accept any other size connector. A good example is when you need to run a cable outside to a surveillance camera and the water-tight housing will not accept a larger field termination plug. If you are forced to go this route, be sure and use cable strain relief boots and be certain of the expected RJ45 8P8C connector fitment. Check out Give it the Boot! Putting Boots onto Ethernet Cable for advice on trueCABLE brand Ethernet cable hardware. The other end of that cable (the switch end) should still be a keystone jack or patch panel, however. Don’t put RJ45 8P8C plugs onto both ends of the cable.
  • ADDITIONALLY, when you have no other choice but to terminate a RJ45 plug onto your Ethernet cable only use the passthrough style for Cat5e and Cat6. Don’t use pass-through plugs for Cat6A. You may have trouble reaching 10G. For Cat6A, defer to the Cat6/6A standard load bar style RJ45 plug and still use the proper strain relief boot. Pass-through plugs, for all of their convenience, are less tolerant of fitment problems than standard RJ45 connectors.

Notes on PoE

The issues that are sometimes seen with Power over Ethernet are not due to pass-through RJ45 plugs. The problem is more elemental than that. The issue is related to poor fitting RJ45 plugs, period. If you have a poor fitting RJ45 plug you will not only experience issues with speed but also with the ability to power your camera or WiFi AP. An additional risk is actual damage to the end-point PoE device, but this is rare. Most PoE devices are using the 802.3af,at, or bt protocol and the switch will not supply power unless the end point device actually requests it. If a bad connection will not allow negotiation, the switch will not apply power, damage is avoided. To be fair to pass-through RJ45 plugs, however, you can get yourself into this situation with standard RJ45 plugs too.

The danger dramatically increases with proprietary PoE where the power is always applied to the cable (called passive PoE) whether the end device requests it or not. The cable run is always “hot”, in other words. I have personally killed a PoE surveillance camera by not paying attention and terminating an RJ45 plug upside down with this sort of PoE. Oh, the wires were in the right color sequence, but the whole plug was upside down…

Wrapping up, I hope that this long technical dissertation brings some clarity to the problems with RJ45 8P8C plugs as a generalized topic. With careful termination practices and knowing what to use where, your Ethernet cable projects will start to get more and more successful. With that, I will say…


trueCABLE presents the information on our website, including the “Cable Academy” blog and live chat support, as a service to our customers and other visitors to our website subject to our website terms and conditions. While the information on this website is about data networking and electrical issues, it is not professional advice and any reliance on such material is at your own risk.

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