Cut romex behind wall

A friend was hanging a new light fixture (replacing an existing one) and accidentally drilled into the romex behind the wall. He found out because when he flipped the switch, the breaker tripped. He removed the new fixture and the screws holding in the metal box, flipped the switch, and the other two lights on the switch came on just fine.
Question. How concerned should he be about the cut romex that is in the wall? Most likely, the wire is not cut, just had some of the insulation scrapped off. In fact, by his best guess (by measuring the resistance) the screw cut into the black wire and not the white. To get access to the romex would be a real pain.
Any suggestions?
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when
and the

lights
wall?
off.
into
real
Something isn't right here. If he was replacing a fixture, what was he drilling for?
If the fault is caused by drilling into the romex, why would removing the new fixture relieve the short?
Between what points was the resistance measured?
Charlie
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Sorry, should have given more info.
The reason for replacing the light fixture was not because there was a problem. The old one looked like crap for years of weather exposure! The fault happened after the new installation.
The existing plastic box had stripped threads where you secure the bracket for the light fixture. He decided to replace the box and all that was available at Home Depot was a metal box with a different mounting hole pattern to secure it to the wall.
His thought is that the short was caused by the new screw that held the box in place, since the box was metal (the old one was plastic) and was grounded to the bare copper wire of the romex.
Removing the screw and the metal box ceased the short.
Before he removed the box, he measured the resistance between the box and the wires. He got about 5 ohms between the box and the white wire and 0.0 from the box to the black wire. There are two other lights controlled by the same switch on that circuit, so the 5 ohms makes sense. The fixture itself is about 10 or 12 ohms, so putting two of them in parallel would result in about 5 or 6 ohms.
Does that make sense?
Assuming that the insulation was scraped off of the black wire, how can he fix that?
Thanks.
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On 11 Aug 2003 19:30:33 GMT, snipped-for-privacy@aol.com.gov (Rileyesi) wrote:

Access it and replace it, or repaire it. Any splices must be made in a junction box, whose cover must be accessable.
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I would love it if I could simply repair it. How do I repair a tear in the insulation in romex? Electrical tape???
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Related question...
I was changing a bunch of outlets to one of the decora style outlets. In one box I discovered that one of the wires was wrapped with electrical tape. I took it off and saw that there was a small nick in the insulation. I re-wrapped it with new tape. Any problems with that repair or do I have to pigtail it with an extension and wire nut which seemed like over kill to me.
(Rileyesi) wrote:

in a

tear in the

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