Hey guys, apologies for late reply, I was down with the flu. @mykepredko, to answer your questions, with USB cables removed, I had no continuity between grounds.
About power line wiring: it is wired exactly as per the Voron 2.4 assembly manual. I double-checked it. To save time on drawing new diagram, I’m just attaching one from the manual. My wiring matches this.
And yes, I do have earth connected to the frame. I used a dremel to expose bare metal on one of the frame members, drilled and tapped an M3 hole, clamped the earth wire with a bolt, and checked for continuity. Both PSUs are mounted to the frame using 3D printed brackets that attach to the DIN rails. Also as per the manual.
@EddyMI3D , thank you for clarification on the markings. My PSUs have “V+” and “V-” marked on them. I must have mistaken that for “+24V” and “-24V” by looking at some examples on the internet or something. My apologies. In any case, multimeter shows 24V between them, so it’s a regular PSU. Same with the 5V one. To answer your last question, I was using 18 gauge from PSU to Octopus. For the EBB36 I am not sure - the wires from the kit I linked to previously, it doesn’t state what gauge it is. For the 5V rails, also 18 gauge.