Detecting Damaged Romex Cable Insulation

Background Scenario:

Part 1) New house with 12-2 romex wiring installed by an electrician who often justified sloppy work with faulty assumptions. Regarding skimpy use of staples: "Them wires ain't going nowhere near the drywall screws but if the inspector says 'sumpin' we'll just tack up another staple here and there to keep 'em happy". I restapled most cable runs but probably missed a few areas --- given several thousand feet of romex used in the house.

Part 2) Thermal/Acoustical Insulation Company comes along yesterday and sprays foam insulation which pushes some of the poorly stapled romex runs outside the stud bays, possibly allowing the romex insulation to be damaged when the excess extruded foam was "trimmed" back to the face of each stud bay by the foam installer. I asked the foam installer to let me know if he cut into any wires by mistake and he agreed to keep me posted, but using a continuity tester I later discovered a low voltage burglar alarm circuit that had been severed, pushed back into the wall and covered with extra foam. An accident? Perhaps, but it raises doubts. Severed wires on 24 gauge circuits are easy for me to detect, but nicked insulation on 12-2 romex is another story.

Part 3) The foam insulation material (Icynene) began to shrink a half-day after installation, totally contrary to the manufacturer's and installer's sales claims, causing me to doubt the honesty and candor and/or knowledge of the insulation company. If they'll misrepresent the merits of their basic product, they probably won't be too forthcoming about collateral damage if/when they can cover it up and hide it from detection... figuring it won't be THEIR problem if someone gets electrocuted or the house burns down several years down the road.

I can't think of any reliable way of determining if any of the romex was damaged without ripping out the foam and visually examining each of the wires and this will be difficult because the foam clings tenaciously to wiring insulation. I'm tempted to do this anyway because of the shrinkage problem but it would be nice to find a way of testing the insulation on each romex circuit without having to scrap away the foam.

Any ideas?

Reply to
Home Builder
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You can test the insulation with an meggar. A unit that put out 500 to a

1000 volts will work. Any scraped wire will be found quickly. Can not be powered up and can not be connected to anything. Recepts and switches ok, lamps no.

I have a Speary that is ancient, AVO is another brand.

Reply to

Think "Romex". A megger won't tell him anything. What are you going to meg it to? Ground? The insulation could be stripped from an area of the hot wire, but there would be no path for the megger current to flow through.

Visual inspection is the only way to do it reliably.

Ben Miller

Reply to
Ben Miller

Romex as it is called (it is actually Nonmetallic Cable 'NM') is very durable cable. It has to pass 13 different UL tests including pulling through joists, crushing, and insulation testing while in water at 5000 volts after having 40 amperes through it for 1 hour while 50 pound weights are hung from it. The UL standard is impressive for NM cable. However, low voltage cables are not tested to this standard, but low voltage class 2 circuits are harmless in a normal dry and nonhazardous environment anyway.

If the workers are experienced craftsmen and if the contractor is bonded I wouldn't worry. However, if your workers are new and working under the table (unlicensed and not bonded), I would be ripping out insulation and performing a visual inspection.

Reply to
Mr. Smith

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