I'm working on a newly framed house with lots of 12-2 romex runs and
plenty of 24/4 wire low voltage runs to burglar alarm sensors at all
windows and doors. Yesterday I arranged for an insulation company to
foam the walls of this house. After the spray process was complete I
offered to help the foam installer trim the foam that had extruded
inside the face of each stud bay. While performing this task, I found
myself cutting into something a good deal harder than foam and realized
that I had managed to saw through one of the burglar alarm circuits that
had become embedded in the expanding foam and pushed outside of the wall
cavity. No problem! I had B-connectors and wire strippers in my
toolkit so I reconnected the circuit and immediately advised the
insulation mechanic to let me know IMMEDIATELY if he encountered (ie
inadvertently damaged) any wiring while trimming the excess foam. He
agreed and I was confident that everything would be ok.

This morning I decided to check all the burglar alarm circuits just for
grins and found a second circuit that had been severed albeit not by me.
The insulation installer, knowingly or unknowingly, had managed to
damage the second circuit, and then (knowingly or unknowingly) had
concealed the damage by spraying additional foam to cover the circuit!
I dug the damaged wires out of the foam and repaired the connections
quickly but I was left with a lingering fear that some of the romex
circuits could have been damaged as well. The insulation installer
could have sawed into a run of romex just enough to damage the
insulation without bothering to warn me about the damage, stuffed it
back into the wall like he did with the burglar alarm wire, and then
covered it with additional foam.

I wouldn't mind a completely cut romex circuit because I could fairly
easily test the entire electrical system before the drywall is taped and
floated and then remove sections of drywall and foam insulation to rerun
any severed cable. However, it would be damn near impossible to cut
completely through 12-2 romex with the type of blade used to trim foam
insulation. What this means is that any damaged would be confined to
the insulation. Very bad!

Why is it so difficult for building tradespeople to simply admit it when
they inadvertently cause or contribute to a problem instead of trying to
cover it up?

Is there a way to identify circuits with bad insulation without visual
inspection?