What Does RJ45 Mean?

RJ45 is one of the most recognised terms in computer networking, yet it is also one of the most misunderstood. Most people use “RJ45” to describe the plastic connector fitted to the end of an Ethernet cable. However, the term originally referred to a registered jack wiring standard developed for telephone systems rather than the Ethernet connector itself.

Today, networking professionals, manufacturers and installers commonly use “RJ45” when referring to the modular connector found on Ethernet cables, even though the connector used for modern Ethernet networks is technically an 8P8C (Eight Position, Eight Contact) modular connector.

Understanding what RJ45 really means helps remove confusion when selecting networking products, terminating Ethernet cables and following structured cabling standards.

Whether you’re installing a home network, expanding a business LAN or selecting professionally manufactured Cat6 Patch Cables, understanding the terminology makes it easier to choose the correct products and follow recognised installation practices.

What Does RJ45 Stand For?

RJ45 stands for Registered Jack 45.

The term “Registered Jack” originated through the Bell System in the United States and later became part of the Federal Communications Commission (FCC) registration system for telecommunications connectors. Each registered jack designation defined a specific connector type and wiring arrangement for telephone services.

Originally, Registered Jack 45 described a keyed telephone connector with a specific wiring configuration. It was not created for Ethernet networking.

As computer networks evolved, the networking industry adopted the familiar modular connector for Ethernet applications. Over time, installers, manufacturers and equipment vendors began referring to the Ethernet connector simply as an “RJ45 connector”, even though modern Ethernet cables actually use an 8P8C modular connector rather than the original RJ45 telephone specification.

Today, the term RJ45 remains the accepted industry name despite its historical origins.

RJ45 vs 8P8C: What’s the Difference?

One of the biggest misconceptions in networking is that Registered Jack 45 and 8P8C mean exactly the same thing.

Strictly speaking, they do not.

Registered Jack 45 refers to a historical registered jack specification.

8P8C describes the physical connector itself:

• 8 Positions – The connector contains eight conductor positions.
• 8 Contacts – All eight positions contain electrical contacts.

Modern Ethernet cables use the 8P8C modular connector because it supports the four twisted wire pairs required for Gigabit Ethernet, 10 Gigabit Ethernet and Power over Ethernet (PoE).

Although “8P8C” is technically correct, the networking industry almost universally refers to these connectors as RJ45 connectors, making both terms widely recognised in practice.

Why are Ethernet connectors Still Used Today?

The term Registered Jack 45 has become deeply embedded throughout the networking industry.

You’ll find it used by:

• Network equipment manufacturers.
• Structured cabling suppliers.
• Electrical contractors.
• IT professionals.
• Telecommunications installers.
• Training organisations.
• Technical documentation.

Because virtually everyone understands what an “RJ45 connector” means, the name continues to be used despite its technical inaccuracy.

For this reason, fibreSales also uses the term RJ45 throughout its networking resources while acknowledging that Ethernet networks actually use 8P8C modular connectors.

Where Are Modular Connectors Used?

RJ45 connectors appear in almost every copper Ethernet network.

Common applications include:

• Desktop computers.
• Network switches.
• Routers.
• Wireless access points.
• VoIP telephones.
• Network printers.
• IP security cameras.
• Network-attached storage (NAS).
• Communications cabinets.
• Data centres.

Many of these devices also support Power over Ethernet (PoE), allowing a single Ethernet cable to carry both data and electrical power. If you’re planning a PoE installation, our Understanding PoE and Ethernet Cables | Complete Guide explains cable selection, power standards and deployment best practices.

Does Registered Jack45 Mean the Same as Ethernet?

Not exactly.

Registered Jack 45 refers to the connector terminology, while Ethernet describes the networking technology that communicates across the cable.

In simple terms:

• RJ45 refers to the connector.
• Ethernet refers to the communication standard.
• Cat5e, Cat6 and Cat6A describe the cable categories.

These technologies work together to create modern Local Area Networks (LANs).

If you’d like to understand how Ethernet networks operate, read Copper Networking Explained | The Complete Guide to Ethernet Networks, which covers Ethernet fundamentals, network architecture and structured cabling concepts in detail.

Engineering Decision

Understanding what RJ45 means helps you choose networking products with greater confidence. Although the term technically originated as a telephone connector specification, it has become the accepted name for the modular connector used on Ethernet networks worldwide.

When purchasing networking products, focus less on the historical terminology and more on selecting components that match your installation. Professionally manufactured Cat6 Patch Cables provide factory-tested reliability for equipment connections, while custom Ethernet cables require compatible RJ45 connectors, quality installation tools and correct termination practices.

How Did RJ45 Become the Standard for Ethernet?

Although RJ45 originated as a registered jack specification for telephone systems, the networking industry adopted the same modular connector format as Ethernet technology evolved. As Local Area Networks (LANs) became the standard for connecting computers, printers, servers and network equipment, the familiar eight-position modular connector proved reliable, cost-effective and easy to manufacture.

Every copper Ethernet network uses what is commonly referred to as an RJ45 connector, regardless of whether the network operates at 10 Mbps, 100 Mbps, 1 Gigabit or 10 Gigabit Ethernet.

This widespread adoption has made “RJ45” the universally recognised name throughout the networking industry, even though the connector itself is technically an 8P8C modular connector.

Professional Ethernet installations should follow recognised standards such as the IEEE 802.3 Ethernet Standard and the ANSI/TIA-568 Structured Cabling Standard to ensure compatibility between network devices and cabling infrastructure.

Why Is RJ45 Important?

RJ45 connectors form the physical connection between Ethernet cables and networking equipment. Without them, devices cannot communicate across a wired network.

You’ll find RJ45 connectors on:

• Desktop and workstation computers.
• Network switches.
• Routers and firewalls.
• Wireless access points.
• Network printers.
• VoIP telephones.
• IP security cameras.
• Network Attached Storage (NAS).
• Smart televisions.
• Industrial networking equipment.

Whether you’re installing a small home office or a large enterprise network, every Ethernet connection relies on properly terminated RJ45 connectors or professionally manufactured patch leads.

For equipment connections where standard cable lengths are suitable, factory-tested Cat6 Patch Cables provide reliable performance while eliminating the need for field termination.

What Does an RJ45 Connector Look Like?

An RJ45 connector is a clear modular plastic plug with eight metal contacts across the front.

Typical features include:

• Eight electrical contacts.
• Plastic locking tab.
• Cable strain relief.
• Conductor channels.
• Cable entry designed for twisted-pair Ethernet cable.

Once installed, the locking tab secures the connector inside the network port, preventing accidental disconnection during normal operation.

Although most people refer to this as an RJ45 connector, it is technically an 8P8C modular connector used for Ethernet communications.

What Devices Use Registered Jack 45 Connectors?

RJ45 connectors appear anywhere wired Ethernet networking is required.

Common examples include:

Permanent structured cabling is normally terminated into Keystone Jacks rather than directly into RJ45 connectors. Equipment is then connected to the network using professionally manufactured Cat6 Patch Cables.

RJ45 and Ethernet Cable Categories

One of the most common misconceptions is that RJ45 refers to a specific Ethernet cable.

It does not.

RJ45 describes the connector terminology, while Cat5e, Cat6 and Cat6A identify the cable category and performance characteristics.

For example:

If you’d like to understand how these cable categories differ, our Copper Networking Explained | The Complete Guide to Ethernet Networks and Can Cat6 Run 10G? provide detailed guidance.

Engineering Decision

Understanding what Registered Jack 45 means helps remove one of the most common sources of confusion in networking. While the term originated from a telephone wiring specification, today’s networking industry uses it almost universally when referring to the modular connector fitted to Ethernet cables.

When selecting networking products, focus on choosing quality components that match your installation requirements. For most switch, router and workstation connections, professionally manufactured Cat6 Patch Cables provide the simplest and most reliable solution. Where custom cable assemblies are required, combine compatible RJ45 connectors with professional installation tools and follow recognised structured cabling standards to achieve consistent, long-term network performance.