norcal, Look in the NEC 2005, Art 334.10, 334.12.
Have you ever seen NM in a commercial building? I haven't,except for someones handymans work, rarely though.
--------------------------------------------Larry Fine, In many commercial/industrial panels there will be 3 phase, 2-120v to ground legs, and 1-208v to ground leg, but they will measure 208 volts between each hot leg. I know the transformers are set up that way, but when would you use the 208v to ground, leg. Most commercial motors are 3 phase 120/208/v or 277/480v, or sometimes 120/208v single phase.
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frenchelectrician, maybe in WW2, but I've never seen 277/480v using NM today.

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