Read this information for the rest of the story from UL:
http://www.ul.com/regulators/knockouts.cfm Are concentric or eccentric knockouts evaluated for bonding?
By Chuck Goetz
Section 250.97 of the National Electrical Code® (NEC®) requires a bonding-type fitting with a bonding jumper to be used when conduits are installed within a concentric or eccentric knockout for non-service conductors in systems rated over 250V. The exception to Section 250.97 allows products that have been Listed for the purpose to have conduits connected to a concentric or eccentric knockout without having to provide additional means to bond the conduit.
In the past, only metallic outlet boxes were Listed by UL for use in these applications. However, UL has now investigated concentric and eccentric knockouts in equipment enclosures covered under other product categories for bonding conduits for non-service conductors without additional means.
The following table summarizes the box and enclosure categories where such an evaluation is available and how to identify compliant products that can be installed according to the exception to Section 250.97.
Category Code
Product Category
Concentric and eccentric knockouts evaluated for bonding?
BGUZ
Boxes, Junction and Pull
Only when product is marked*
CYIV
Cabinets and Cutout Boxes
Only when product is marked*
QCIT
Metallic Outlet Boxes
All products comply
* Products Listed for these applications are provided with a marking, such as "Concentric (or eccentric) knockouts suitable for bonding conduits for non-service conductors."
Cabinets and cutout boxes are used in many end-product applications, including "Enclosed Switches (WIAX)," "Panelboards (QEUY)," and "Industrial Control Equipment (NIMX)," and may additionally be evaluated for bonding through concentric or eccentric knockouts. Installers and regulatory authorities should therefore look for the above referenced marking to determine if the concentric or eccentric knockouts have been investigated for bonding in lieu of requiring bonding jumpers.
For more information on bonding applications involving concentric or eccentric knockouts in cabinets, cutout boxes, junction and pull boxes, contact Chuck Goetz in Northbrook, Ill., by phone at +1-847-664-3163; or by e-mail at Charles.A.Goetz@us.ul.com.
For more information on bonding applications involving concentric or eccentric knockouts in metallic outlet boxes, contact George Walbrecht in Northbrook, Ill., by phone at +1-847-664-3126; or by e-mail at George.F.Walbrecht@us.ul.com.
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