Let this tale put things in perspective ...
In 1967, a very competent electrician - the firm was the same one that got the "Ufer" into the NEC - installed several panels side-by-side. The panels were connected to each other with nipples and locknuts.
Thanksgiving, 2004 .... I get the call that this customer has lost power to half the building and UPS alarms were going off. Many 'surge suppressor' power strips had failed.
Ever look at the obvious for hours and not see it? Fail to see the elephant in the room? That's how I spent my Thanksgiving.
What had happened was .... the guy had not separated the ground from the neutral in the adjoining panels- instead, treating the whole assembly as a 'main panel.' Over time, simple corrosion and vibration had set the stage for one of those nipples to lose good contact with the sheet metal. High impedence ground = open neutral.
Power down, separate the neutrals from the grounds, run a few feet of wire between the panels ... and all was good. The IT department noted that all their 'power quality' issues had also disappeared. Imagine that.
This happened with opposing locknuts on each enclosure. Now, do you really want to claim that one locknut, alone, is enough to secure things?
