Which ethernet cable do I need — Cat5e, Cat6 or Cat6a?

Cable categories describe how well the twisted pairs inside resist interference and crosstalk, which sets the combination of speed and distance the cable can carry. That is the whole story. A higher number does not make your broadband faster, it raises the ceiling — and if your broadband is 500 Mbps and your cable can carry 1,000, the ceiling was never the limit.

Step by step

1. Work out the fastest thing that will ever use this cable.Your broadband speed is one factor, but so is traffic that never leaves the house — copying to a network drive, or a games console pulling from a local server. If everything is a gigabit or less, the category question is already settled.
2. Measure the run honestly.All of these categories manage a gigabit at the full 100 m structured cabling limit, which is far beyond anything in a house. Distance only becomes a discriminator at 10 Gbps, where Cat6 is limited to a shorter run and Cat6a is not.
3. Decide whether the cable is replaceable.This is the real question. A patch lead between a router and a console can be swapped in ten seconds, so buy the cheap one. A cable chased into a wall or run under a floor is there for twenty years, so pay the small extra for Cat6 or Cat6a and never think about it again.
4. Check the conductors are solid copper.Copper-clad aluminium is common in cheap cables, is more brittle, has higher resistance, and performs poorly with power over ethernet. Look for pure copper or solid copper on the listing. This matters far more than the category number.
5. Pick solid core for fixed runs, stranded for patch leads.Solid core carries signal better over distance but breaks if repeatedly flexed, so it belongs in walls terminated to sockets. Stranded survives being moved and belongs in the short leads at each end.
6. Ignore shielding unless you have a reason.Shielded cable needs shielded connectors and a proper earth path to do anything, and done wrong it is worse than unshielded. In a house, unshielded is correct unless the cable runs alongside mains for a long distance.
7. Buy the right connector arrangement for the job.For a permanent run, terminate into wall sockets at both ends and use short patch leads — far more reliable than crimping plugs, and repairable. For a temporary run, buy a moulded patch lead of the right length rather than making one.

Tips

• A network switch is how you turn one router port into several. Any unmanaged gigabit switch works, needs no configuration, and plugs into a spare LAN port on the router. Buying one with more ports than you need costs almost nothing.
• Flat cables are convenient under carpet and doors but usually have thinner conductors. Fine for a short patch, not for a long permanent run.
• Length costs you nothing in performance at these distances, so buy a cable a metre longer than you measured rather than one stretched tight.
• If a run may ever carry a camera or an access point, plan for power over ethernet — it uses the same cable and removes the need for a socket at the far end.

Questions people ask