Eccentric, concentric knockouts & bonding

[Jpflex]

I was wandering if someone could better explain the rules on bonding raceways to cabinets with eccentric or concentric knockouts, whether for services or 250.97 circuits over 250 volts to ground?


One of my grounding and bonding books says that ALL eccentric or concentric knockouts must be removed and reducing washers used if needed prior to using bonding bushings or similar listed bonding equipment for conductive conduit on the line side of service or for conductive conduit for equipment with circuits over 250 volts to ground?

Apparently the exception to not be required to remove all knockouts is if they are listed for bonding. What is the purpose of having smaller knockouts if they all have to be removed and a reducing washer used? Does equipment often detail if their knockouts are permitted for bonding and if so do we leave the smaller knockouts in while inserting conduit?

 

[augie47]

wander no more

UL QCRV:
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, ‘‘National Electrical Code,’’ for raceways containing other than service conductors. Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been certified for bonding purposes may be used with reducing washers without all knockouts being removed.

 

[Jpflex]

wander no more

UL QCRV:
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, ‘‘National Electrical Code,’’ for raceways containing other than service conductors. Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been certified for bonding purposes may be used with reducing washers without all knockouts being removed.

Would you still need to use a reducing washer if the eccentric or concentric knockouts were certified for bonding or couldn’t I just punch the proper size knockout needed for the size of conduit and use standard lock rings to bond the conduit with the appropriate listed fitting such as a set screw connector?

Also do the majority of manufactures often detail or list if their cabinet knockouts are suitable for bonding?

 

[infinity]

Also do the majority of manufactures often detail or list if their cabinet knockouts are suitable for bonding?

None are for over 250 volt to ground. Only boxes are so listed.