Actually, to add to my post, I've never used 2 chase nipples between panels. I've use one chase nipple to an LB, where our inspectors require a bonding wire to the j box. This would bond the j box and pipe and LB up to the panel. With two chase nipples as stated, a bonding wire would only bond the panels and, if there was poor contact at the chase nipples to the panels, the coupling and chase nipples could concievably become energized with no grounding path.
