Panels connected with metal conduit considered same assembly?

[CuriousHomeInspector]

I believe I have been told this (erroneously) several times. Time and time again I see feeder circuits from the panel containing the service disconnect device with 3 wires that supply other panels that have ground to neutral loads and the grounded conductor acting as the EGC. The exception that is told to me is that two panels that are connected with metal conduit and are within 6 ft of each other are considered part of the same panel assembly. I find this nowhere in the NEC, nor have ever received this in writing. It is my impression that once you leave a portion of a listed panel and go to another piece of equipment, they are considered separate. Of course entire assemblies that are listed as an assembly is one piece of equipment, right?

I think the confusion comes in due to 2015 NEC 250.118(2) which allows metal conduit (of course properly installed) to serve as the EGC. In the "sub panel" (panel fed by the feeder) it would still require the EGC and the grounded conductor to be separate and isolated, but could be accomplished with 3 wires, and the 4th "wire" being the conduit itself.

Is this an accurate assessment?

 

[augie47]

I know of no Code section that would allow sub-panels, regardless of proximity to the service panel, to allow Neutral to equipment ground connections.

 

[CuriousHomeInspector]

But for clarification, rigid metal conduit (or flexible metal conduit when installed under certain conditions for that matter) could serve as the EGC? Of course while remaining isolated and separate from the grounded conductor.

 

[augie47]

yes