An Ethernet cable looks like a larger version of a phone cord — a flexible jacket (usually blue, black, or grey) with clear rectangular RJ45 plugs at each end, each holding eight gold pins.
- RJ45 plug has all eight gold pins visible
- Connector clicks securely into an Ethernet port
- Cable is under 100m (330 ft) for Cat5e or Cat6
- Pins are bent, missing, or corroded
- Plugged into a phone (RJ11) jack by mistake
- Cable category is too low for the required speed
Key Physical Features
Ethernet cables are easy to spot once you know what to look for. The jacket is round and flexible, typically 5–8mm thick, and most commonly blue, grey, black, or yellow. At each end sits a clear plastic RJ45 connector — slightly wider than a phone plug — with a small locking tab on top that clicks into place.
Look through the clear plug. You should see eight tiny gold pins arranged in a single row. Those pins correspond to four twisted wire pairs inside the cable. All eight must be intact for Gigabit (1000 Mbps) speeds. Missing or damaged pins drop performance to 10/100 Mbps or kill the connection entirely.
RJ45 vs RJ11: Don’t Mix Them Up
The most common mix-up is confusing an Ethernet RJ45 plug with a phone RJ11 plug. Here’s how to tell them apart at a glance:
| Feature | RJ45 (Ethernet) | RJ11 (Phone) |
|---|---|---|
| Width | ~11.7mm | ~9.5mm |
| Pins | 8 | 4 or 6 |
| Port label | LAN / Ethernet | LINE / TEL |
| Use | Network data | Phone line |
An RJ45 plug will not fully seat in a phone jack, and forcing it can damage both connectors. Always match the wider RJ45 to a port marked with the Ethernet symbol (three connected lines) or labelled LAN.
Cable Categories and What They Look Like
The category is usually printed along the cable jacket — look for text like Cat5e, Cat6, or Cat6a. Higher categories use tighter wire twists and sometimes add internal splines or foil shielding, making them slightly stiffer. Netgear’s Ethernet cable guide explains how category ratings map to speed and distance limits.
- Cat5e — thin, flexible; supports up to 1 Gbps at 100m
- Cat6 — slightly stiffer; supports up to 10 Gbps at 55m
- Cat6a — thicker, often shielded; supports 10 Gbps at 100m
If you’re also connecting displays or adapters alongside your network setup, you may find our guides on whether USB-C can connect to HDMI and whether USB-C supports video output useful for building a complete desk setup.
Quick Visual Checklist
- Rectangular clear plug — wider than a phone connector
- Eight gold pins in a single row inside the plug
- Locking tab on the top of the plug
- Category text printed on the jacket
- Round, flexible cable — not flat like a phone extension cord
Bottom line: An Ethernet cable is identified by its wider RJ45 connector, eight visible gold pins, and category markings on the jacket. If the plug has fewer than eight pins, won’t click into your LAN port, or the jacket shows no category label, it’s either a phone cable or a damaged Ethernet cable — replace it before troubleshooting your connection.