How does NEC 725.144 address cable bundling for PoE?

Power over Ethernet pushed enough current down 23 and 24 AWG pairs that heat became a real problem inside large bundles. Section 725.144 is the code response. It applies to Class 2 and Class 3 circuits that transmit power and data to a powered device where the current exceeds 0.3 amperes per conductor.

How the table works

Table 725.144 gives the maximum current per conductor. You enter it with three things: the conductor gauge, the number of 4 pair cables in the bundle, and the temperature rating of the cable. Bundle size bands step down as the count rises, running through groups such as 1 to 7, 8 to 19, 20 to 37, 38 to 61, 62 to 91, 92 to 192, and above 192. A higher cable temperature rating, 75 degrees C or 90 degrees C instead of 60 degrees C, buys back a meaningful amount of current, which is why data center specs call out higher rated cable.

The practical consequence is that a bundle of 100 cables in a tray does not support the same per port current as a bundle of 12 in a J hook. Designers who size for 802.3bt class 8 devices at high port counts run into the table quickly.

The LP option

Section 725.144(B) covers cables with the LP, or limited power, marking. An LP cable is listed and marked with a maximum current per conductor, for example CMP-LP(0.6A). Those cables may be installed in bundles without the ampacity adjustment of Table 725.144, provided the current per conductor does not exceed the marked value. On a large PoE build, specifying LP cable is usually cheaper than redesigning pathways to keep bundles small.

Practical bundling

Beyond the table, keep bundles loose and let air move. Common field practice is to break large bundles into groups and to avoid tightly cinched ties, which is also good for the cable geometry and return loss. Section 300.11 still governs support, so bundles cannot be laid on a suspended ceiling grid or supported from the ceiling support wires under 300.11(B). Section 725.24 requires Class 2 and Class 3 cables to be supported by the building structure in a neat and workmanlike manner.

Separation still applies

Section 725.136 keeps Class 2 and Class 3 conductors out of enclosures, raceways, and cables with electric light and power conductors except under the specific conditions listed. Bundling PoE tighter does not change that separation requirement.

Field takeaway

Check Table 725.144 with your gauge, bundle count, and cable temperature rating before committing pathways, or specify LP marked cable and design to its marked current instead.