725.144(B) Use of Class 2-LP or Class 3-LP Cables to Transmit Power and Data.
Code Change Summary: Code language revisions were made to provide clarity on the application of LP (Limited Power) cables transmitting both power and data.
Power Over Ethernet (POE) is an increasingly popular way to take a data cable such as a Cat 5 or Cat 6 and use it to power things like LED lighting or other low energy consuming equipment that can operate at limited voltage levels.
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.
A listed data cable marked with “LP” on the jacket has been subjected to additional testing beyond that of a normal data cable to see how it performs when bundled tightly with other cables that are also carrying power and data. Many regular data cable types are permitted to carry both power and data by the NEC®, but a special allowance is given in 725.144(B) for those listed with the LP designation.
In the 2020 NEC®, a Section 725.144(B) was revised to clarify the proper application of Class 2 and Class 3 cables with the LP suffix that transmit power and data. The previous 2017 language was a bit confusing when applying ampacity Table 725.144 and led the code reader to think that a LP cable with a marked current level of .5 amps for example, could never be used at a higher ampacity than .5 amps.
An LP cable marked with a current rating of .5 amps for example, means that even if the number of LP cables in a bundle exceeds 192 (the max number of cables mentioned in Table 725.144), the LP cable still has an ampacity of .5 amps.
If six LP cables are bundled without maintaining spacing for example, Table 725.144 is then used to determine the ampacity of the LP cables rather than the marked current rating of the cable. In many cases, the table values might yield a higher allowable ampacity for the cable than its marked current rating.
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 2020 NEC® edition of NFPA 70.
2017 Code Language:
725.144(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:
Informational Note 1: The “(xxA)” following the suffix -LP indicates the ampacity of each conductor in a cable.
Informational Note 2: An example of a limited power (LP) cable is a cable marked Type CL2-LP(0.5A), 23 AWG. A Type CL2- LP(0.5), 23 AWG could be used in any location where a Type CL2 could be used; however, the LP cable would be suitable for carrying up to 0.5 A per conductor, regardless of the number of cables in a bundle. If used in a 7-cable bundle, the same cable could carry up to 1.2 amperes per conductor.
(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.
2020 Code Language:
725.144(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 from a power source with a rated current per conductor up to the marked current limit located immediately following the suffix “-LP” and shall be permitted to transmit data to the equipment. Where the number of bundled LP cables is 192 or less and the selected ampacity of the cables in accordance with Table 725.144 exceeds the marked current limit of the cable, the ampacity determined from the table shall be permitted to be used. For ambient temperatures above 30°C (86°F), the correction factors of Table 310.15(B)(1) or Equation 310.15(B) shall apply. 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 current limit 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 current limit.
(3) System design shall be permitted by qualified persons under engineering supervision.
Informational Note: An example of a limited power (LP) cable is a cable marked Type CL2-LP(0.5A), 23 AWG.