I found this in 2005 NFPA99 Health Care Facilities. It appears to address protection from damage rather than grounding.
4.3.2.2.5.1 Wiring for low-voltage control systems and nonemergency communications and signaling systems shall not be required to be installed in metal raceways in anesthetizing locations.
THIS PRECEEDED THE ABOVE PARAGRAPH:
4.3.2.2.5 Low-voltage wiring shall comply with either of the following:
(1) Fixed systems of 30 V (dc or ac rms) or less shall be ungrounded, provided the insulation between each ungrounded conductor and the primary circuit, which is supplied from a conventionally grounded distribution system, is the same protection as required for the primary voltage.
(2) A grounded low-voltage system shall be permitted provided that load currents are not carried in the grounding conductors.
Comments?