725.144 Transmission of Power and Data.
Code Change Summary: A new code section was added to address limited energy cables that carry power and data.
A movement is occurring to push data cables to the limit. Power Over Ethernet (POE) is an increasingly popular way to take a data cable such as a Cat 5 or Cat 6 cable and use it to power things like LED lighting or other low energy consuming equipment that can operate at limited voltage levels.
Lighting and other equipment currently exists today that can be supplied by running low voltage cables from a patch panel that contains a Class 2 power supply. Switches or occupancy sensors are then installed and also connected to the same patch panel to provide lighting control. This same patch panel may also serve as the central hub for computers, video cameras and other signal circuits.
As the application of POE becomes more prevalent, so also does the opportunity for misapplication of the cables outside of the scope of their rating or current carrying capacity.
In the 2017 NEC®, a new section was added to address Class 2 and Class 3 circuits that transmit power and data to a powered device. Along with the new section, new ampacity Table 725.144 was added which provides the maximum allowable ampacity of such cables based on the size of the individual conductors and the number of cables in a bundle.
For these types of installations, it is very common to see cables severely bundled with little or no opportunity for heat dissipation. Using the new table will help by limiting the allowable ampacity as the number of cables in a bundle increases.
Section 725.144(B) provides rules on special low voltage cables that have been tested and listed for limited power (LP) applications. These cables get additional wiggle room since they have been evaluated and found to be able to perform within their marked current rating regardless of the number of cables in a bundle.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2017 Code Language:
N 725.144 Transmission of Power and Data. The requirements of 725.144(A) and (B) shall apply to Class 2 and Class 3 circuits that transmit power and data to a powered device. The requirements of Parts I and III of Article 725 and 300.11 shall apply to Class 2 and Class 3 circuits that transmit power and data. The conductors that carry power for the data circuits shall be copper. The current in the power circuit shall not exceed the current limitation of the connectors.
(A) Use of Class 2 or Class 3 Cables to Transmit Power and Data. Where Types CL3P, CL2P, CL3R, CL2R, CL3, or CL2 transmit power and data, the following shall apply, as applicable:
(1) The ampacity ratings in Table 725.144 shall apply at an ambient temperature of 30°C (86°F).
(2) For ambient temperatures above 30°C (86°F), the correction factors of 310.15(B)(2) shall apply.
(B) Use of Class 2-LP or Class 3-LP Cables to Transmit Power and Data. Types CL3P-LP, CL2P-LP, CL3R-LP, CL2R-LP, CL3-LP, or CL2-LP shall be permitted to supply power to equipment at a current level up to the marked ampere limit located immediately following the suffix LP and shall be permitted to transmit data to the equipment. The Class 2-LP and Class 3-LP cables shall comply with the following, as applicable:
(1) Cables with the suffix “-LP” shall be permitted to be installed in bundles, raceways, cable trays, communications raceways, and cable routing assemblies.
(2) Cables with the suffix “-LP” and a marked ampere level shall follow the substitution hierarchy of Table 725.154 and Figure 725.154(A) for the cable type without the suffix “LP” and without the marked ampere level.
(3) System design shall be permitted by qualified persons under engineering supervision.
See actual NEC® text for informational notes.