Code Change Summary: Revised code language regarding the temperature rating of Liquidtight Flexible Metal Conduit (LFMC).

A new change in Section 350.10 now allows conductors or cables to be installed in a LFMC raceway even if the conductors have a higher temperature rating than the raceway itself. The catch is the conductors cannot be operated at a temperature higher than the listed temperature rating of the LFMC.

This language aligns with similar requirements brought into the 2005 NEC^® for rigid nonmetallic conduit (RNC) such as schedule 40 and schedule 80 PVC raceways in 352.10.

Although the 2020 language in 350.10(4) is new, the concept is not. This is an age-old principle of the weakest link theory. It wouldn’t make sense to have a conductor with a maximum temperature rating of 250˚C operating near its high temperature capacity and installed in a raceway with a maximum temperature rating of 80˚C.

Alternately, there’s nothing wrong with installing a conductor with a maximum temperature rating of 250˚C in a LFMC raceway with a maximum temperature rating of 80˚C as long as the conductor will never operate above the maximum temperature rating of the raceway.

If the ampacity of a conductor (with a higher insulation temperature rating than the LFMC raceway enclosing it) is selected using the temperature column in the ampacity table that aligns with the temperature rating of the LFMC, reasonable assurance can be achieved that the conductor will not operate above the maximum temperature of the raceway.

Designers often specify a more robust cable or conductor with a high temperature rating even if it will never operate near its maximum rated temperature.

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.