Getting confused now

[joeyww12000]

Ok guys been reading some threads and codebook on concentric and eccentric KO's in regards to the use of bonding bushings for conduits containing service conductors. When entering a panel,120/208, with flexible metal conduit from a transformer do I need to use bonding bushings? Ive not noticed any on the jobs Ive been on lately, just the use of locknuts to attach the connectors to panel and transformers. Is there a difference in whether I knockout my own holes or if I use KO's supplied already?

 

[M. D.]

http://ecmweb.com/mag/electric_stumped_code_44/

EC&M 2007
Q. When are bonding bushings required on metal electrical raceways?

A. Bonding bushings are one of the methods that can fulfill the NEC requirements for bonding of service raceways, 277/480V systems, and in hazardous (classified) locations. Here are some details:

• When a metal service raceway terminates to an enclosure with a ringed knockout, a listed bonding device (such as a bonding wedge or bonding bushing) must bond one end of the service raceway with a bonding jumper sized in accordance with Table 250.66 [250.92(B)(4) and 250.102(C)]. If ringed knockouts are not encountered, you can use a bonding locknut instead of a bonding wedge or bonding bushing.
• Metal raceways or cables, containing 277V or 480V circuits, terminating at ringed knockouts must be bonded to the metal enclosure with a bonding jumper sized in accordance with Table 250.122, based on the rating of the circuit overcurrent protection device [250.97, 250.102(D)].
• Because of the explosive conditions associated with electrical installations in hazardous (classified) locations, electrical continuity of the effective ground-fault current path (metal parts of equipment and raceways) must be ensured by one of the methods specified in 250.92(B)(2) through (4). A bonding bushing is one of the acceptable methods [250.100].