Can MTW wire be ran in conduit or is it strictly to be used for wiring in a panel?
We would be installing the wire between our control panel and motor and running it in conduit.
In my experience MTW use is best when it conforms to NFPA 79.
My opinion is Yes! (without specific reference to the Code) To clarify, the NEC (NFPA-70) & NFPA-79 go hand in hand.
* The NEC is "to-and-from" the Control Panel, where
* The NFPA-79 is "inside" the Control Panel.
Taking into consideration those Exceptions and Special Applications (i.e. Class I, Div II - Intrinsically Safe), one example might be a 20HP (3-Ph, 480VAC) where 430.22 says "not less than" 125% (of 430.6(A)(1) - use Table 430.250) = 34A.
While MTW in the Panel might be 8AWG (Table 12.5.1), using 3-Wires in Conduit, see Table 310.15(B)(16) and (at least - in my opinion), a typical max. Ambient Temp. 96F Correction Factor listed in Table 310.15(B)(2)(a):
* THHN = 10AWG --> [27A(125%) / (0.91) = 37A] Column 90C
* MTW = 6AWG --> [27A(125%) / (0.82) = 41A] Column 60C
I use MTW Rating at 60C because it's the worst case scenario (or Best Practice). While Article 100 describes "Location, Wet" as underground, and "Location, Damp" as moisture, there is not much on the argument considering condensation, water based lubricants, the possibility of a Sprinkler going off, roof leaks or even Compressed Air blow down.
So just where do I get the impression that MTW can be used outside the Panel?!?
Here is a code reference:
310.10 Uses Permitted. The conductors described in 310.104shall be permitted for use in any of the wiring methods coveredin Chapter 3 and as specified in their respective tables or aspermitted elsewhere in this Code.
MTW is listed in 310.104. So there you have it.
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