Rockwell Automation 1512B MV Controllers, 200/400A Two-High Cabinet, Standard and Arc-Resistant Enclosure - Manual (Page 93)

Rockwell Automation Publication 1500-UM055G-EN-P - May 2013 85
ArcShield Plenum Installation Instructions Appendix B
Figure 87 - Optional Extension/Elbow with Vertical Extension (Right side exit)
After the Extension/Elbow assembly is attached through the fastener holes on
the inside flange of the Plenum, the front duct section can be replaced and
fastened through the holes on the outside flanges.
Last Plenum in line-up remains
open for installation of
extension assembly