If you’re building, repairing, or upgrading a wired network, learning how RJ45 connectors work is one of the most useful skills you can pick up. A correctly terminated RJ45 connector ensures stable, high-speed Ethernet performance—while a simple wiring or crimping mistake can cause slow speeds, random disconnects, or a cable that doesn’t work at all. This guide walks you through everything you need to know: RJ45 connector types, T568A vs T568B colour (color) code, wiring diagrams, pinouts, choosing the right connector for Cat5e/Cat6, shielded vs unshielded options, pass-through connectors, installation steps, testing, troubleshooting, and best practices for both DIY users and installers.
Quick takeaway: Use T568B on both ends for most modern networks, keep wire pairs twisted as close to the connector as possible, ensure wires are fully seated, crimp firmly, and always test with a cable tester before deploying the cable—especially in walls or ceilings.
What Is an RJ45 Connector (and Why It’s Often Called 8P8C)
The “RJ45 connector” is the familiar modular plug used for Ethernet networking. Technically speaking, most Ethernet connectors are 8P8C connectors—meaning 8 positions and 8 contacts. Over time, “RJ45” became the common name people use for Ethernet plugs and jacks, even though “RJ45” originally referred to a specific telephone interface standard.
In practical terms:
- RJ45 plug = the clear plastic male connector at the end of a patch cable
- RJ45 jack = the female port on a switch, router, wall plate, patch panel, or device
- 8P8C = the physical connector format used for Ethernet wiring
Don’t worry—if you’re wiring Ethernet cables, you’ll see “RJ45” everywhere and it’s perfectly acceptable to use that name.
RJ45 Connector Types (Plug vs Jack vs Keystone vs Coupler)
RJ45 connectors come in several forms depending on where and how you’re installing Ethernet.
1) RJ45 Plug (Male)
This is the most common connector for patch cables. You crimp it onto the end of Ethernet cable (Cat5e, Cat6, Cat6a, etc.) to create custom-length cables.
Use cases:
- Custom patch cords / patch leads
- Direct cable runs to devices (temporary)
- Equipment-to-switch connections
2) RJ45 Jack (Female)
An RJ45 jack is the port you plug into. Some are built into devices, while others are standalone components.
Use cases:
- Panel mount connectors on enclosures
- Surface mount network ports
- Inline coupler style female connectors
3) Keystone Jack
A keystone jack is the modular jack used in wall plates and patch panels. It snaps into a keystone opening and is typically terminated using a punch-down tool (IDC termination) rather than crimping.
Use cases:
- Structured cabling in homes/offices
- Wall plates, patch panels, faceplates
- Permanent Ethernet installation
4) RJ45 Coupler / Female-to-Female Adapter
A coupler connects two Ethernet patch cords or extends a cable temporarily. Quality matters here—cheap couplers can increase loss and may impact performance at higher speeds.
Use cases:
- Temporary cable extension
- Quick repairs without re-terminating
- Connecting two patch leads (patch cords)
RJ45 Wiring Standards: T568A vs T568B Colour (Color) Code
When wiring RJ45 connectors, you’ll use one of two standards:
- T568A
- T568B
Both standards use the same wire colours (colors) and the same four twisted pairs, but the order of the green and orange pairs is swapped.
Which standard should you use?
- T568B is the most common in the US and many commercial networks worldwide.
- T568A is sometimes used in residential installations and in environments where it matches older telecom schemes.
Most important rule:
✅ Use the same standard on both ends for a straight-through Ethernet cable.
If you wire one end T568A and the other end T568B, you create a crossover cable. Modern equipment often supports Auto-MDI/MDIX (automatic crossover), but for consistency and troubleshooting, straight-through wiring is still the default choice.
RJ45 Wiring Diagram (Pins 1–8 Table)
Hold the RJ45 plug with the clip facing down and the contacts facing up. Pin 1 is on the left.
Below is the colour (color) code order for each standard from Pin 1 to Pin 8:
T568A Wiring Order
- White/Green
- Green
- White/Orange
- Blue
- White/Blue
- Orange
- White/Brown
- Brown
T568B Wiring Order
- White/Orange
- Orange
- White/Green
- Blue
- White/Blue
- Green
- White/Brown
- Brown
Tip: For most DIY and professional installs, pick T568B and use it consistently.
RJ45 Connector Pinout Explained (and How Ethernet Uses the Pairs)
Ethernet cabling contains four twisted pairs:
- Pair 1: Blue / White-Blue
- Pair 2: Orange / White-Orange
- Pair 3: Green / White-Green
- Pair 4: Brown / White-Brown
How different Ethernet speeds use the pins
10/100Base-T (10Mbps / 100Mbps):
- Uses only two pairs: pins 1–2 and 3–6
- The blue and brown pairs are not used for data (but may be used for PoE)
1000Base-T (Gigabit Ethernet):
- Uses all four pairs (all 8 wires)
- This is why cables with missing or poorly crimped wires often “drop” to 100Mbps
2.5G/5G/10G (Multi-Gig / 10GbE):
- Uses all pairs and is more sensitive to installation quality
- Keeping twist, using correct connectors, and minimizing untwist becomes increasingly important
PoE (Power over Ethernet) notes
PoE can carry power over:
- “Spare pairs” on some older PoE schemes (10/100 networks), or
- All pairs in modern standards
In practice:
✅ Standard T568A/T568B wiring still applies for PoE—don’t invent a special wiring scheme. Focus on correct termination and connector quality.
Choosing the Right RJ45 Connector (Cat5e/Cat6, Solid vs Stranded, Shielded, Pass-Through)
Not all RJ45 connectors are identical. Choosing the correct plug for your cable type is crucial—especially for Cat6 and for long-term reliability.
1) Cat5e vs Cat6 vs Cat6a Connectors
- Cat5e connectors: Usually accept smaller conductor sizes and are easier to terminate.
- Cat6 connectors: Often require tighter tolerances and may include a load bar to separate pairs.
- Cat6a connectors: Designed for thicker cable and better performance at 10GbE.
Best practice: Match your connector category to your cable category (Cat6 cable → Cat6-rated connector).
2) Solid vs Stranded Cable (very important)
- Solid conductor cable: Used for in-wall runs and structured cabling.
- Stranded conductor cable: Used for flexible patch leads (patch cords).
RJ45 plugs are often designed for one or the other because the metal contact pins bite into the conductor differently. Using the wrong plug can cause intermittent issues.
✅ If you’re making patch cords, use stranded cable + stranded-rated plugs
✅ If you’re terminating in-wall cable, consider keystone jacks instead of plugs
3) Shielded vs Unshielded (UTP vs STP/FTP)
- UTP (Unshielded Twisted Pair): Most common; best for typical home/office environments.
- STP/FTP (Shielded): Better for high-interference environments, industrial spaces, dense cable bundles, or where EMC is a concern.
Shielded connectors typically have a metal shell and require proper bonding/grounding in the overall cabling system to be effective. Don’t mix shielded and unshielded components unless you understand the grounding implications.
4) Pass-Through RJ45 Connectors
Pass-through connectors allow the wires to pass out the front of the plug before crimping, making it easier to verify the order.
Pros:
- Faster for beginners
- Easier to confirm correct colour (color) sequence
- Often reduces termination errors
Cons:
- Requires a compatible pass-through crimper
- Poor trimming can cause shorts or failures
- Slightly more expensive per connector
If you’re making many cables or training new techs, pass-through is often worth it. More about how to choose RJ45 connectors.
Tools You Need to Install RJ45 Connectors
To terminate RJ45 connectors properly, you’ll want:
- Cable stripper (or a crimper with stripping blade)
- RJ45 crimping tool
- Flush cutter / scissors for clean wire trimming
- Cable tester (basic continuity tester at minimum)
- Optional but helpful: pass-through cutting crimper, cable jacket gauge, and a small flashlight
A tester is the biggest time saver. Without one, you’ll spend more time guessing and re-crimping.
How to Crimp an RJ45 Connector (Step-by-Step Installation)
Here’s the installation process for a standard RJ45 plug.
Step 1: Strip the Cable Jacket
Strip about 1–2 inches (2.5–5 cm) of jacket.
Avoid nicking inner conductors.
Step 2: Untwist and Arrange the Wires
Untwist each pair only as much as needed.
Arrange the wires in T568A or T568B order.
✅ Keep twists as close to the jacket as possible (ideally within 0.5 inch / 1.3 cm).
Step 3: Flatten and Trim Evenly
Press the wires together between your fingers to flatten.
Trim the ends so all wires are the same length.
Step 4: Insert Wires into the RJ45 Plug
Hold the plug with the clip down.
Slide wires in carefully until they hit the end.
Checkpoints:
- All wires fully seated
- Correct colour (color) order
- Jacket goes inside the plug so the strain relief can grip it
Step 5: Crimp Firmly
Insert the plug into the crimper and squeeze firmly.
A good crimp pushes pins into conductors and locks the jacket.
Step 6: Repeat on the Other End
Use the same wiring standard unless you intentionally need a crossover cable.
How to Test an RJ45 Cable (and Read the Results)
Plug both ends into a cable tester:
- Master unit + remote unit
A typical tester will light pins 1–8 in order if the wiring is correct.
Common test results
- Pass (1–8 sequential): Correct cable
- Open: A wire isn’t connected (bad crimp or wire didn’t seat)
- Short: Two conductors touch (often from messy trimming or pass-through cuts)
- Miswire: Wires swapped (wrong order)
- Split pair: Conductors are in the correct pin order but wrong pair grouping (causes signal problems)
Split pairs are especially dangerous because basic continuity testers may not catch them reliably at speed.
Common RJ45 Wiring & Crimping Mistakes (Fix Guide)
Here are the most common causes of failure:
1) Wrong Colour (Color) Order
Fix: Cut off and re-terminate. Don’t try to “move one wire.”
2) Wires Not Fully Inserted
Fix: Ensure copper reaches the front of the plug before crimping.
3) Too Much Untwist
Fix: Keep twists close to jacket to reduce interference.
4) Jacket Not Inside the Plug
Fix: Make sure the crimp grabs the jacket, not just the wires.
5) Wrong Plug Type (Solid vs Stranded)
Fix: Use a connector designed for your conductor type.
6) Uneven Wire Lengths
Fix: Trim cleanly and evenly before inserting.
7) Bad Tooling
Cheap crimpers can produce weak crimps. For frequent work, invest in reliable tools.
FAQ: RJ45 Connectors, Wiring, and Installation
- Is RJ45 the same as 8P8C?
Often yes in everyday Ethernet use. Technically, Ethernet uses the 8P8C modular connector. - Should I use T568A or T568B?
Use one standard consistently. T568B is most common and a safe default. - Does wiring order affect speed?
Yes. Gigabit and above require all 8 wires to be correctly terminated and paired. - What is a split pair?
A split pair happens when pins are correct but wires are paired incorrectly—causing interference and poor performance. - Are pass-through RJ45 connectors better?
They’re easier and faster for beginners, but require the right tool and clean trimming. - Do RJ45 couplers reduce speed?
Quality couplers usually work fine at gigabit. For 10GbE, use high-quality Cat6a-rated couplers and minimize coupler use. - Do I need shielded connectors at home?
Usually no. Use shielded connectors only when you use shielded cable and have a good reason (high EMI). - Can RJ45 carry PoE?
Yes. Correct wiring supports PoE; focus on quality connectors and cable. - Can I crimp Cat6 cable with Cat5e plugs?
Sometimes, but it’s not recommended. Use Cat6-rated plugs for Cat6 cable. - What’s the best way to ensure my cable works?
Use a tester every time. It saves time and prevents hidden failures. - How long can an Ethernet cable run be?
Standard maximum is typically 100 meters for many Ethernet standards (including patch leads). Installation quality matters. - What’s the most common reason a DIY cable fails?
Wires not fully seated or wrong colour (color) order.
US vs UK/EU Terminology & Buying Tips
RJ45 connectors work the same worldwide, but terminology differs slightly. In the US, you’ll often see “patch cord,” while in the UK and parts of the EU “patch lead” is more common—both refer to the same Ethernet cable with RJ45 plugs. Likewise, US documentation may say “jack” or “keystone jack,” while UK/EU installers may refer to “network modules,” “outlets,” or “structured cabling components.” Buying habits can differ too: UK/EU installers often prefer trade packs or bulk quantities, and may pay closer attention to compliance marks and structured cabling practices. For best results, match your connector to your cable category (Cat5e/Cat6/Cat6a), choose the correct plug type for solid vs stranded conductors, and keep your wiring standard consistent across your installation.
Summary
An RJ45 connector (commonly used for Ethernet) must be wired using the correct T568A or T568B colour (color) code to ensure stable network performance. For most installations, use T568B on both ends to create a straight-through cable. RJ45 wiring follows an 8-pin (8P8C) pinout, and gigabit Ethernet requires all four twisted pairs (8 wires) to be terminated correctly with minimal untwist. This guide covers RJ45 connector types (plug, jack, keystone, coupler), wiring diagrams, pin order, Cat5e/Cat6 connector selection, shielded vs unshielded options, and step-by-step crimping, testing, and troubleshooting to produce reliable patch leads (patch cords).
