277 volts & 120 volts in same 12x12 junction box??

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tommyh

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Colorado
277 volts & 120 volts in the same junction box (without barrier)

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Question: Can I run 277 volt ckts & 120 volt ckts in seperate conduits, but then they terminate in one 12x12 junction box for lighting and power purposes.

Is that legal?? per NEC 2008? I thought as long as the insulations of all wires is 600 volts or less it's ok??

RE: Now someone told me that if you have say, one conduit with (600 volt rated wires) @ 277 volts in a juntion box and another conduit with (600 volt rated wires) @ 120 volts in that "same" junction box:

He said that if between the two voltages it reads over 300 volts it's illegal???
So a 277 volt leg metered to 120 volt leg (in that same junction box)
= 397 volts (over 300 volts)

Where is that in the new 2008 NEC, or is he wrong?? Need help guys!!
 
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