Figure 619 may have needed a machinist to drill and tap the plug.
Might the porcelain knob supporting the cable off the tee/plug made it an early space-age "isolated ground"?
In all seriousness, does anyone else remember a more recent “drilled and tapped” from the inside hole and screw for grounding? It was illustrated in a more recent NEC handbook. Its purpose was to provide a “legal” equipment-ground termination where buried PVC was connected to above-ground GRC and a class-1 j-box for explosion-proof equipment.
[This message has been edited by Bjarney (edited 03-13-2004).]
