Here is the practical reference for Ethernet network cabling: the RJ45 color codes (T568A and T568B), the difference between straight-through and crossover cables, and the table of cable categories (Cat5e to Cat8) with their speeds and distances. Keep it handy.
RJ45 Color Codes: T568A and T568B
An RJ45 connector has 8 pins. Two standards define the wire order: T568A and T568B. T568B is the most common. Golden rule: use the same standard at both ends to get a straight-through cable.
| Pin | T568A | T568B |
|---|---|---|
| 1 | White/Green | White/Orange |
| 2 | Green | Orange |
| 3 | White/Orange | White/Green |
| 4 | Blue | Blue |
| 5 | White/Blue | White/Blue |
| 6 | Orange | Green |
| 7 | White/Brown | White/Brown |
| 8 | Brown | Brown |
Straight-Through or Crossover Cable?
- Straight-through cable: same standard at both ends (T568B ↔ T568B). This is the standard cable to connect a computer, printer, or camera to a switch or router.
- Crossover cable: T568A on one end, T568B on the other. Historically used to connect two identical devices (PC to PC, switch to switch). Today, the auto-MDI/MDIX feature of equipment makes crossover cables almost unnecessary.
Ethernet Cable Categories
| Category | Max Speed | Frequency | Distance | Typical Use |
|---|---|---|---|---|
| Cat5e | 1 Gbps | 100 MHz | 100 m | Common networks |
| Cat6 | 1 Gbps (10 Gbps ≤ 55 m) | 250 MHz | 100 m | Recommended standard |
| Cat6a | 10 Gbps | 500 MHz | 100 m | 10G over 100 m |
| Cat7 | 10 Gbps | 600 MHz | 100 m | Shielded (S/FTP) |
| Cat8 | 25 to 40 Gbps | 2000 MHz | 30 m | Datacenter |
Shielded (STP) or Unshielded (UTP)?
UTP cable (unshielded) is sufficient for most indoor installations. Prefer STP/FTP (shielded) in noisy environments: near electrical cables, industrial settings, outdoor passages.
Cable and PoE
PoE (Power over Ethernet) runs through Ethernet copper: count on Cat5e minimum for PoE/PoE+, and Cat6 to be safe. To size your installation, see our PoE guide and our PoE budget calculator.
FAQ: RJ45 Cabling
T568A or T568B: which to choose?
T568B is the most common. It doesn’t matter which you use, as long as both ends of a straight-through cable are identical.
Is the crossover cable still useful?
Rarely: almost all modern equipment supports auto-MDI/MDIX and accepts a straight-through cable, even between two switches.
Which cable category should I choose?
Cat6 is the default good choice. Upgrade to Cat6a if you want 10 Gbps over 100 m.
What is the maximum length of an Ethernet cable?
100 meters for copper, all categories combined (except Cat8, limited to 30 m). Beyond that, fiber is required.
For equipment, browse our network switches and our SFP modules (for fiber), and read our Ethernet switch guide and fiber or copper guides.