Short answer: IEEE’s objectives target 2.5 Gb/s over 100 m of Cat5e and 5 Gb/s over 100 m of Cat6. For 10 Gb/s, Fluke Networks advises Cat6a for new installations meant to carry it up to 100 m; quoting the TIA, it puts Cat6’s reliable reach at that speed at 37 m. Whatever you buy, avoid copper-clad aluminium (CCA) cable sold as Cat5e or Cat6; the section below explains why.

What the categories mean

The category printed on a cable’s jacket tells you what it’s built to carry, and over what distance. The speeds that matter at home come from IEEE’s Ethernet work. Its objectives for 2.5 and 5 Gb/s Ethernet target 2.5 Gb/s over at least 100 m of Cat5e, and 5 Gb/s over at least 100 m of Cat6 (and over Cat5e in defined cases). For 10 Gb/s, the original 2003 objectives aimed for at least 55 m to 100 m over Cat6-class cable.

The full speed-by-category table, and how every link in the chain affects the speed you get, is in our guide to multi-gig Ethernet.

10 Gb/s: where Cat6 and Cat6a differ

Fluke Networks, quoting the TIA’s TSB-155 bulletin, says 10 Gb/s Ethernet should work over up to 37 m of Cat6, and between 37 and 55 m depending on alien crosstalk, which is interference between neighbouring cables; longer runs may need mitigation.

For full-length runs, Fluke says that if you’re specifying a new installation to carry 10 Gb/s up to 100 m, you should be looking to the Category 6A specification. Fluke’s 2014 article reports the TIA’s limits rather than its own measurements.

Avoid copper-clad aluminium

Some cable is labelled Cat5e or Cat6 but uses copper-clad aluminium wire instead of solid copper. Fluke Networks quotes the Communications Cable and Connectivity Association saying these cables should not be called category cable, because they don’t meet the standards that require solid copper conductors.

It matters beyond the label. Fluke says CCA has higher electrical resistance than copper, doesn’t support Power over Ethernet applications because of that higher resistance, and doesn’t have a valid safety listing under the US National Electrical Code. If you plan to power an access point or camera over the cable, see what PoE is; solid copper is the safer choice. To spot genuine cable, Fluke suggests checking the packaging for a UL or ETL listing mark.

What to buy

Our recommendations, based on the figures above:

  • Existing Cat5e: keep it for 2.5 Gb/s and below. If a wired device is slower than expected, the cable is one suspect among several: see not getting the speed you pay for.
  • New patch cables: Cat6, which IEEE’s objectives target for 5 Gb/s over 100 m.
  • New in-wall runs: Cat6a if 10 Gb/s is a possibility; Cat6 if you’re sure 5 Gb/s will do.
  • Any cable: solid copper with a listing mark, never CCA.

Not sure a cable run is the right fix at all? Ethernet, MoCA or powerline compares the ways to get a wired connection to another room.