What's Wrong Here?

Jul 1, 2004 12:00 PM, By Joe Tedesco, NEC Columnist

How well do you know the Code?

Hint: The circuit in this raceway supplies a 3-phase, 480V piece of equipment.

John Dennehy, lead electrician, ABM Engineering, Plainsboro, N.J., correctly identified several violations with this installation. “I see a violation of 250.97 for assured bonding for a 480V circuit,” he wrote. “There is a ringed knockout present, which means that a bonding jumper based on 250.122 is required. I would also cite 110.12 for a violation of neat and workmanlike installation. I would also mention 110.10 for maintaining a low-impedance path and 250.4(A)(5) for an effective ground fault path.”

Paul Dunphy, electrical and compliance inspector, engineering and utilities, Harvard University, Cambridge, Mass., offered this comment. “The raceway for the 480V circuit violates 250.92(B),” he wrote. “Standard locknuts shall not be the sole means of support for bonding required by this [installation]. 250.92(B) is referenced by 250.97, Bonding for Over 250V.”

Steve Schilling, master electrician, Chesapeake Smart Homes, Stevensville, Md., also weighed in. “According to 250.97, for circuits of over 250V to ground, electrical continuity of metal raceways and cables shall be maintained by methods approved in 250.92(B) and the Exceptions listed in 250.97,” he wrote. “This would mean that an ‘approved fitting with shoulders that seat firmly against the box’ should've been used. Or if the enclosure is approved for the purpose, there would need to be a ‘bonding bushing’ with a bonding jumper run to the can to maintain a positive ground path. (It appears that neither of these measures was taken.) The Article states that standard locknuts or bushings shall not be the sole connection. In this picture, it appears that the concentric knockout is close to coming apart, which would leave no reliable raceway ground path.”

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