I found the clause this morning in MIL-HDBK-411B "POWER AND THE ENVIRONMENT FOR SENSITIVE DOD ELECTRONIC EQUIPMENT" which discourages set-screw type couplers for EMI reasons. As luck would have it, this MIL-HDBK is approved for public release and distribution unlimited, so I'll copy/paste the section: (It's OCR from a scanned-in pdf, so excuse the typographical errors)
MIL-HDBK-411B: 5.5.6.5.1 Perferred conduit types. Shielding of communications and data circuits from ac-generated noise is improved by enclosing all power conductors in metallic conduit or continuous metallic duct. Ac fault protection and ac power conductors will not be enclosed in the same conduit with communications and data cables. There are three general types of metallic conduit acceptable for power distribution for critical DoD communications and computer facilities: rigid, flexible, and thin wall. Poly-vinyl -chloride (PVC), or similar nonmetallic construction, is not acceptable for power distribution where high reliability is a requirement. Metal conduit with set-screw type connectors should also be avoided. For maximum shielding effectiveness, metal conduit with threaded connectors should be used. To maintain this effective shield, all joints between sections of conduit should be treated with a conductive lubricant or caulk. All power conduits must be sized to accommodate the phase conductors, neutral conductor, and a fault protection conductor (green wire).
Interesting, another MIL-HDBK prohibits use of EMT for any conductor over 1/0 size... Either way, it appears our policy was for EMI reasons, vice safety grounding or mechanical reasons.
[This message has been edited by SteveFehr (edited 11-29-2005).]
