Q: What is LP testing? What is an LP rating?
A: LP (Limited Power) testing is a test procedure for determining how many amps a conductor can accommodate. LP testing was developed by Underwriters Laboratories (UL) to provide a standardized method of testing to which cable manufacturers could submit their cables. LP testing is not required by the National Electrical Code (NEC) in the U.S. It is an optional method of testing that cable manufacturers can use to promote the power carrying capacity of their cables. Typical results for 4-pair Category style communication cables (such as Cat 5e, Cat 6, Cat 6A and Cat 7) range from .5 amps per conductor to .9 amps. UL then permits the cable manufacturer to print the LP rating on the cable jacket. The intent is to aid contractors and end users in determining how much power a given cable can accommodate. An alternative to LP testing is to use an Ampacity chart provided in section 725 of the 2017 NEC. The Ampacity chart, along with information printed on the cable jacket can help determine the estimated power carrying capacity of the cable. As more and more devices receive their power over low voltage Category cables (known as Power over Ethernet or PoE), knowing what load the cable can safely carry is important.