Is it possible to find wire insulation faults without a visual exam?

[Home Builder]

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?

[Anthony Straight]

Yes. The equipment you need is commonly called a Megger. It applies a high voltage (usually under 500v -- NM cable insulation is good for up to 600v) and measures very small leakage currents to ground. It takes some experience to give you the best results, and isn't absolutely accurate. You may be able to rent one, but I recommend having an electrician who knows how to use it and interpret the readings test your wiring for you.

[cornytheclown]

Well..the insulators dont want to hang around while you repair the damage is the most likely reason they just cover up the mistakes. They might get paid by the job and have another one to get too or they simply dont want to hang around while someone fixes the damage.........who know ???

What I cant understand is why with so many wires going into a house today a person wouldnt use conduit in the walls that are being insulated with the foam. It would make repairs or modifications down the road a whole lot easier.... I know not all the wires...control and fire/burgler alarm probably cant be 100 percent protected by conduit.....but I would still get what I could in conduit if I was filling the wall with foam insulation.

Lastly....Why were the wires not secured properly in the first place. I have never seen wires run by professionals in a matter where you could pull it out past the face of the stud bay ??? surely they stapled the romex to the studs and at least used some kind of insulated fastener for the control or alarm wires.