From 2011 NEC:
Article 240
"(3) 3-Phase and 2-Phase Systems. For line-to-line loads
in 4-wire, 3-phase systems or 5-wire, 2-phase systems, individual single-pole circuit breakers rated 120/240 volts ac with identified handle ties shall be permitted as the protection for each ungrounded conductor, if the systems have a grounded neutral point and the voltage to ground does not exceed 120 volts."
There are other mentions within '11 I turned up via a search thru the PDF version. Most of them are specific to an installation. (DC; Bulk storage, etc)
