I cannot pretend to understand metal boxes and the strange things that happen when you drill holes and run wires through them. Putting the whole circuit through a single hole sounds like a good idea, balance things out, like an earth leakage trip.

OTOH, sounding like a good idea is not always enough. Recently there was a lovely picture doing the rounds of a plated steel nut and bolt holding an earth loop to a copper bus bar. Should have used copper, they used to use copper nuts and bolts in that golden age of understanding when I were a lad. In the picture dissimilar metals had formed a thermocouple. The earth loop probably only gave a fraction of a Volt but the current was enough to heat the nut red hot