Quick Answer: Four-pair Cat 6 UTP is rated to 250 MHz and carries 1000BASE-T, 2,5GBASE-T, 5GBASE-T and PoE++ at up to 90 W, but 10GBASE-T reaches only 55 m on it; Cat 6a is needed for 100 m. The pairs are fixed: 1-2 and 3-6, then 4-5 and 7-8. Two-pair PoE stops at 30 W, while 60 W and 90 W need all four pairs. Keep the installed bend radius at four times the cable diameter, untwist no more than 13 mm at the jack and leave 3 dB of margin at 250 MHz.
A Cat 6 cable fails at 2,5GBASE-T far more often than at 1000BASE-T, because the higher rate uses the same four pairs at wider bandwidth. The cable is rarely the fault. The termination is. One split pair, one 40 mm untwisted tail or one crushed bend and the pair-to-pair symmetry that 10GBASE-T depends on is gone.
Which pair goes where
Data on all four pairs
1000BASE-T, 2,5GBASE-T, 5GBASE-T and 10GBASE-T all transmit and receive on four pairs at once, so a four-pair cable has no spare conductor. 1000BASE-T delivers about 940 Mbit/s of payload, 2,5GBASE-T reaches 2500 Mbit/s, and 10GBASE-T needs Cat 6 to 55 m or Cat 6a to 100 m.
Power on two pairs or four
PoE at 15,4 W per port and PoE+ at 30 W use two pairs, with the spare pair set carrying the return. PoE++ at 60 W and 90 W divides current across all four pairs, roughly 0,6 A per conductor at 90 W. That is why 23 AWG solid copper is specified and copper-clad aluminium is not.
Comparing the grades before you buy
Quotes for cat6 lan cables usually differ by jacket and by test margin rather than by copper. The two numbers that change a design are reach at 10G and heat under PoE++.
| Grade | Rated bandwidth | 10GBASE-T reach | PoE++ at 90 W |
|---|
| Cat 5e UTP | 100 MHz | Not supported | Allowed, runs warm |
| Cat 6 UTP | 250 MHz | 55 m (180 ft) | 0,6 A per conductor |
| Cat 6 F/UTP | 250 MHz | 55 m (180 ft) | Shield bonded both ends |
| Cat 6a UTP | 500 MHz | 100 m (328 ft) | Larger outside diameter |
| Cat 6a F/UTP | 500 MHz | 100 m (328 ft) | Shielded, 10 mm approx |
Jacket, pathway and bend radius
Choosing CMR, CMP or CL2
CMR is the riser grade for vertical shafts, CMP is required in plenum air space such as a return air ceiling, and CL2 covers Class 2 circuits. A run through a ceiling void used for return air without conduit needs CMP whatever the data rate. Read the legend printed on the jacket, not the invoice.
Pulling and dressing
Keep the installed bend radius at four times the cable diameter, about 25 mm for a 6,2 mm jacket, and do not exceed 25 lbf (110 N) of pulling tension. Cable ties should be snug but not deforming, and a bundle of 24 cables wants support every 1,5 m (5 ft) on a horizontal run.
Bonding, shields and the sales claims
A UTP cable has no drain wire and no shield, so there is nothing to bond and no earth kit to buy. Claims about bonded pairs describe a manufacturing tweak to pair geometry, not an electrical function, and they do not lift the 55 m limit. The procurement question behind is lan cable same as ethernet is simpler: the assembly is identical, only the job description changes. Where the route crosses a machine room or a loading bay, specify armored cat6 cable for crush resistance.
Reading the tester instead of the datasheet
A permanent link test at 250 MHz should return insertion loss, NEXT, return loss and ACR-F with at least 3 dB of margin. A pass with 0,2 dB of margin usually means a 40 mm untwisted tail or a kink behind the jack. Links under 15 m often show poor return loss at the far end, which is a termination fault rather than a short cable.
Practical scenarios
- Situation: a 60 m (197 ft) run to a 10G access point on Cat 6 exceeds the 55 m limit. Either shorten the route by 8 m or move to Cat 6a; a 2,5GBASE-T port at 100 m is the cheaper compromise.
- Situation: 24 PoE++ cameras at 90 W each put 2,16 kW of heat along one tray. Use 23 AWG solid, space the bundle off the ceiling and measure the tray temperature before adding a 25th camera.
- Situation: a link passes 1000BASE-T and fails 5GBASE-T. Re-terminate both ends with 13 mm of untwist and re-test NEXT at 250 MHz before condemning the cable.
- Situation: a run crosses a return air ceiling above a server room. Fit CMP jacket rather than CMR and skip the conduit; the cost difference is per metre, the code difference is a failed inspection.
FAQ
Can Cat 6 do 10GBASE-T at 100 m?
No. The standard allows 55 m on Cat 6 and 100 m on Cat 6a. Vendors quote longer figures for short bundles in cool cabinets, but that is a laboratory condition, not a installed link with margin.
Does a shielded cable need earthing?
A shielded or foiled cable needs the shield bonded at both ends to be useful, which means a proper panel and jack with a drain connection. Fitted to unshielded hardware it becomes an aerial for interference.
How much untwist is acceptable at a jack?
13 mm is the working limit for Cat 6, and less is better above 250 MHz. The pair twist is what holds the impedance and the balance, so every extra millimetre of parallel conductor costs margin.
