EGC twist .

Years ago, I went to T/S a shock complaint in the two bathrooms at a home. I found that the EGC of an incoming NM cable at a 2g switch box in the hall had broken at the sheath, probably damaged when the cable was first stripped and installed.

With the twisted but non-wire-nutted EGCs pointing upward, the broken wire had screwed itself down the rest of twisted bare wires over time, until it stopped when it just happened to touch a switch screw, energizing the entire downstream circuit's EGCs.
 
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