Flexible Metal Conduit to be listed if installed as protection for Class 1 circuits


Dear forum members :bye:,

my name is Marc and I am an electrical engineer from Germany.

I am actually working on my second project for a machinery unit that shall be installed in the USA and where all electrical devices and installations have to be in accordance with NEC edition 2014.

In my first USA project, we were allowed to use Class II circuits for the control circuits of the machinery unit by project specifications what made it much more easy but this time unfortunately we are not.

This time, we plan to use 24VDC, 4A UL listed overcurrent protection devices in the Unit Control Panel so that the control circuits of the field instruments can be classified as class 1 circuits NEC.

As a standard, some of the control circuits at our machinery unit are protected by flexible metal conduits, what causes my problem, because our standard conduit for this machine is an extra oil resistant one that is not listed by an NRTL.

If I read NEC Article 350 (LFMC), a listing for LFMC and fittings is required. Otherwise 725.3 (Class I, II, III) says, only referenced articles from (A)-(L) have to be considered from chapter, what means article 350 requirement would not be valid for Class I installation.

On the other hand, article 725.46 says, wiring methods for class I circuits to be in accordance with chapter 3 of NEC, what means, article 350 and the coreespong listing requirements are valid.

I am actually not sure, which way of thinking is correct :blink:.

I hope, anyone has experiences and can help me.

Great thanks in advance! Have a nice day and greetings from Germany!


Smart $

Esteemed Member
...I am actually not sure, which way of thinking is correct :blink:...
You have to comply with 725.46.

725.3 is a general requirement for Article 725 matters. It covers other article compliance requirements for Class 1, 2, and 3 circuits. 725.46 is a specific requirement covering Class 1 circuits only.