Wire break diagnosis help
As guy that did this trade all his working life, I can DEFINITELY tell you that these proximity / non contact voltage detectors ARE NOT to be depended upon 100%.

They have their place and time, and they are to be treated as such. I have a Fluke™ Volt Alert 1AC-A II and while it's a great tester, it definitely is not the "End-All" of testers and it cannot ever be replaced by a wired / probe / lead tester.

I use these proximity testers for "quick and dirty" GENERAL testing purposes.

Get yourself a Fluke™ T5-1000 from Home Depot or Lowe's