RJ45 vs Keystone: What's the Difference and Which Should You Use?

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

When installing a structured cabling system (SCS) you are presented with multiple Ethernet termination methods and they are definitely not all equal. Apart from significant differences in how you terminate 8P8C modular plugs (aka RJ45 plugs) vs the average keystone jack, the decision on what Ethernet cable connector you use can have a dramatic impact on LAN (Local Area Network) performance and reliability.

This blog is aimed at helping everyone from the beginner to the seasoned professional with Ethernet termination selection at various points in a well constructed and up to the standard local area network installation. For both termination types we will discuss:

• Technical differences
• Use cases
• Pros/cons of keystone jack vs RJ45
• Impact upon overall system performance and reliability

What is an RJ45 Connector?

The term “RJ45 connector" is actually incorrect, but a term that refuses to die. We won’t go over the history and usage of the term and how things ended up this way, but instead surrender to calling this type of termination hardware “RJ45” for clarity. Just know that the correct term is 8P8C modular plug (8P8C means eight position / eight contact) and to use that term when around super technical people who might (and likely will) correct you. You are warned!

So, that out of the way the RJ45 is a type of male connector. This male connector terminates the copper conductors of copper twisted pair communications cable (Category cable like Cat6, etc.). RJ45 connectors plug into a modular wall jack, often and again incorrectly referred to as a “ethernet wall jack”.

Ethernet is not technically a cable, but a communication protocol. How the term “Ethernet” became conflated with physical cable is yet another story we won’t cover here.

Terminate means to establish electrical contact at the end of a cable, for example.

Typical use cases for a RJ45 connector

• Terminated at both ends of an Ethernet cable, functioning as a patch cable (also called patch cord or equipment cord) to plug into a keystone jack or directly into a powered device like a router or Ethernet switch
• Terminated at single end of an Ethernet cable, to plug into a PoE (Power over Ethernet) device such as a Wi-Fi access point or surveillance camera

RJ45 Modular Plug Characteristics

• Not Category rated, selection is entirely dependent on fitment and shielding
• May be shielded or unshielded and may be terminated onto shielded or unshielded cable
• Provides eight positions for copper conductor termination, utilizing insulation displacing golden contact pins
• Displaces insulation from the sides of conductor, longitudinally, straddling the conductor metal
• Extremely sensitive to proper cable jacket and insulated conductor fitment
• Requires attention to detail and good workmanship to function properly
• Hand terminated RJ45 modular plugs are often a source of reliability and performance issues for the uninitiated

What is a Keystone Jack?

The term “keystone jack” in a LAN is technically referred to as modular jack. As you might have guessed, this is the “female” receptacle where you plug patch cords in.

In a modern structured cabling system keystone jacks are found mounted in patch panels and remote outlets. Keystone jacks are designed to terminate both ends of permanently installed communications cable. Technically, this communications cable can be copper twisted pair Category (Ethernet) cable, fiber optical cable, and more. Permanently installed cable is normally hidden from view and found inside walls and run through pathways such as conduits. There are many variations of keystone jacks, so we need to specify which one we are going to talk about. For clarity and simplicity, we will continue to discuss traditional copper Category cable with eight conductors such as Cat5e, Cat6, Cat6A, etc. Proceeding with this example, the keystone jack would be known as a 8P8C modular jack.

This female connector terminates the eight copper conductors of copper twisted pair communications cable on one side, while providing a female port on the other side to plug RJ45 connectors into.

Keystone jacks are foundational to correct structured cabling system installation, performance, and long term reliability.

8P8C modular keystone jack shown during the process of termination to solid copper Ethernet cable

Keystone jack mounted in a keystone jack wall plate and plugged into a patch cord. This is how a “remote outlet” functions.

Typical use cases for a keystone jack

• Terminated at both ends of permanently installed solid copper Ethernet cable, functioning as the permanent link
• Mounted into patch panels and wall plates, providing the ability to patch into a LAN with a patch cord
• Terminated at the head-end of a permanently installed Ethernet cable where the remote end is terminated to a RJ45 connector plug, functioning as a MPTL or Modular Plug Terminated Link

Modular Keystone Jack Characteristics

• Are Category rated and should be matched by Category to the cable being terminated
• House a PCB (Printed Circuit Board) to increase performance
• May be shielded or unshielded and may be terminated onto shielded or unshielded cable
• Provides eight positions for copper conductor termination, utilizing insulation displacement “knives”
• Displaces insulation from the sides of conductor, at right angles, piercing the conductor metal
• Wide Ethernet cable compatibility; not excessively sensitive to proper cable jacket and insulated conductor size
• Easy to terminate and will normally have the color code order printed on the jack housing to facilitate the correct T568A or T568B wiring order
• With a modicum of care and attention detail, keystone jacks are rarely the source of reliability and performance issues

Once the permanent link is patched into at both ends, you now have the “channel”.

The concept of permanent links and channels are absolutely crucial to understanding how properly constructed structured cabling systems look and work. Please see Calculating Ethernet Cable Overall Channel Length for Success.

Key Differences -- Keystone Jacks vs RJ45 Modular Plugs

When Should You Use a Keystone Jack vs RJ45 Plug?

• When constructing a permanently installed structured cabling system terminate the solid copper Ethernet cable to modular keystone jacks, and use a patch panel to mount the keystone jacks for performance and organization
• In unique situations, such as when a single end of a link needs to power up and pass data to a PoE device, termination of a RJ45 plug at the remote device end is often necessary
• AVOID termination of RJ45 modular plugs to both ends of solid copper conductor Ethernet cable--defer to factory produced and Certified pre-terminated Ethernet patch cords for that task

Make use of keystone jacks, patch panels, and Certified patch cords to the maximum extent possible. There is no reason why a residential LAN should perform less reliably than any other.

Common Mistakes and Misconceptions

Misconception: Keystone jacks and patch panels are for big “professional” networks and can be safely ignored for more “regular” installations.

Reality: Nothing could be further from the truth! Performance and reliability are important regardless of the size of the network.

Misconception: “Normal” Ethernet cable is terminated to RJ45 plugs at both ends.

Reality: Patch cable is terminated to RJ45 plugs at both ends. Preferably, patch cable is also factory terminated and Certified. Permanently installed cable should not leverage patch cable unless the circumstances are unique and there is no other choice.

Mistake: Not knowing when to call in a professional installer.

If your installation is commercial in nature, you are best off to contract a firm that specializes in structured cabling systems with BICSI Certified installers. There is a dizzying array of “gotchas” such as local Codes, and bonding/grounding considerations that are typically well beyond the capabilities of IT professionals or even casual installers. If your installation is residential, but you are dealing with closed walls that require “fishing” cable you are again better off calling a professional to deal with that. The professional installer will have the training, tools, and experience.

Misconception: IT personnel and structured cabling systems installers are one in the same.

Reality: IT personnel focus on the logical structure of the network, and often do not have a full understanding of how to properly install a structured cabling system. SCS installers focus on the physical structure of the network and may not understand how to properly set up any powered LAN equipment. IT and SCS installation are two different disciplines.

Conclusion

So there you have it! Keystone jacks and RJ45 plugs both have their place, but where and when you use them depends on what you are doing. Generally speaking, a correctly installed structured cabling system will make use of a network rack (or wall mounted patch panel in a residential setting), permanently installed solid copper Ethernet cable, keystone jacks at the patch panel and remote ends, and finally factory Certified patch cords to patch into the permanent links. The concept is rather foreign at first, but once you have been exposed to the concept and why this is the correct path forward you will come away with an appreciation for the structured approach.

Unfortunately much of this information has been opaque to all but highly trained and certified installers, with such information and training hidden behind heavy duty price tags. trueCABLE is on a mission to make this profession more accessible and understandable.

Here is some additional recommended reading:

Beginner's Guide to Network Cables
How Far Can You Run an Ethernet Cable? Maximum Length Explained
Facts About Ethernet Cable Jacket Ratings
How To: Install Copper Ethernet and Coaxial Cable for Success

HAPPY NETWORKING!

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