Your Dielectric Withstand Test uses 677 Vdc (or 479 Vac). If the test passes it will confirm that the smallest gap between exposed conductors in the cable is likely greater than 0.003 inches (0.08 mm). If the test fails you may have a gap less than 0.003 inches (0.08 mm). If the DWV test is done in helium then the test might detect a gap as large as 0.083 inches (2.11 mm).
This is for a heater bank in a oven that is going through a pass through. I am talking about phase to ground and I would also like to know about phase to phase. Is there any standard for air gaps ver. voltage? I have a probe that is about 1/8" away from ground and I do not want it to arc.
Post your question in the electrical forum. There are probably code required air gaps that far larger than than what you would calculate based on first principles. Why would you not use a ceramic insulator on a wire passing through a steel wall?
