250.97 Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).
Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:
(2) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
Some inspectors want this whenever the raceway is the sole bonding means on any line voltage circuit.
The words in 300.10 Make it very hard to install RMC or IMC using only one locknut (assume it's not a bonding locknut) and maintain continuity of the grounding conductor if the raceway is the grounding conductor. I would not approve an installation of RMC or IMC using a single standard locknut on the inside of an enclosure and nothing on the outside.
300.10 NEC 2008 Edition
Last edited by George Little; 02/18/1209:13 PM. Reason: Typo
if a single lock nut is used and the conduit is secured then i can't fail the inspections.
Sure you can. "secured" is one of those terms that end up being defined by the AHJ. They could easily call this "loosely jointed" and want to see bonding jumpers with bushings. Lock nuts are cheap, Use 2 and make everyone happy.