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
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.
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.
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