48vdc wiring methods (help)

[Richard S]

We have a customer that installed some 48vdc circuits using single conductor MTW cables in ladder rack and basket type tray. The inspector inquired if cable was type TC (tray cable). Typically single conductors smaller than 1/0 are not TC rated and 392.3(B)(1) for 2008 NEC states that single conductors shall be 1/0 or larger. My initial thought was that they were out of luck, but I've see lots of telecommunications installations in the past that were similar. Does anyone have any experience with 48vdc circuits where article 392 will not be applicable? Article 720 is for Circuits and Equipment Operating at Less than 50Volts, but doesn't give much guidance. 720.11 "Circuits operating at less than 50volts shall be installed in a neat and workmanlike manner. Cables shall be supported by the building structure in such a manner that the cable will not be damaged by normal building use." ??? Does that mean article 392 is not applicable to circuits less than 50volts??

 

[petersonra]

I don't see any exemption in 720 that would allow you to run smaller conductors in a cable tray than what is normally allowed.

maybe the answer is to put the conductors in smurf tubing. not real cheap, but probably the cheapest answer you are going to get.

 

[hillbilly1]

We use a multi conductor cable on the installs we have done, customer supplied, so I haven't looked to see if it is cable tray rated. They don't get inspected since their a utility.