Tracing short in electrical circuit

I'm hoping someone can point me in the right direction in troubleshooting this electrical problem. We had an electrician rough in the electrical for a family room addition and kitchen remodel. The kitchen lighting consists of six four-inch recessed lights with a max bulb of 50W on a 15 Amp breaker along with two pendant lights and undercabinet lighting. The cans are on one single pole switch which I installed and has been working fine for several weeks. The pendants and undercabinet lights are yet to be installed. The other night my wife went to flip the switch and she said it made a popping noise, sparked and tripped the circuit breaker. When I got home I reset the breaker and flipped the switch- no sparks but the CB did immediately trip again. Thinking it might be a bad CB I shut off the 50 Amp breaker in the main box that supplies the subpanel for the addition and replaced the 15 amp breaker. I flipped the light switch and again the breaker tripped. I've tested the switch with a continuity tester and it checks out OK, even though I put another switch on just to be sure and still the same thing. I've climbed up into the attic and checked the connections in the three lights that are accessible and everything looks good. Unfortunately the other three lights are not accessbile without cutting into the sheetrock from below. All the romex that I can see looks fine, no breaks in the insulation. I'm at a loss for what to check next. The electrician that did the rough in is very busy and won't be available for at least a couple of weeks. Any suggestions are appreciated.
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dale martin wrote:

It seems like what you have there is a short condition. In this case since it worked for a time was something moved or disturbed? Are the undercabinets and pendents roughed in to the same circuit? How were the feeds terminated? You need to isolate where the short is occurring. If all the paths to the new work look good including the terminations to the work to be completed. I would open up the feed to the three cans you can't access from the attic. this would be done at the last junction box. Then test the breaker if it holds the problem is in those 3 hidden cans. BTW often you can access the junction boxes in these, depends on the make. Richard
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most probable dumb answer: remove bulbs and examine their sockets for arc burns or short. leave bulbs out of their sockets and check sockets for power from switch.
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A quick update. Following this advice I went around the kitchen and pulled the bulbs. One bulb looked kind of suspect, just a little brown at the solder where the metal base meets the glass. I left one bulb in and flipped the CB on. When I flipped the light switch, no tripping of the CB and the bulb lit up. I then replaced all the bulbs except the suspect one and again everything worked without a hitch. Tonight I will buy a new bulb and see what happens when I put it in the fixture where the possible problem exists. Thanks for the help.
buffalobill wrote:

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dale martin wrote:

That sure beats a nail/screw through the wire ANY day!!! Hope that's it...
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dale martin wrote:

What does your wife mean by "it?" Ask her where the noise and sparks came from. I would expect to see some carbon deposits in that area.
Are the pendents and undercabinet lights going to be fed by the same switch? If so, check the tied off wiring there to see if its tied off correctly.
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dale martin wrote:

Were nail plates used? Is it possible a nail was driven into the romex? Otherwise inspect all exposed wiring to make sure a wire clipping has not lodged somewhere. WIth the circuit breaker pulled (for safety) you might try an ohmmeter.
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OK. You are in the middle of a remodel, right? What was being done just prior to the time your wife turned on that switch and discovered the problem? Could very well be a nail or screw through a wire. Did you use wire shields on all the exposed penetrations? Also: Don't take that crap from the electrician. A shorting situation like this could cause a fire if you keep trying to use the bad circuit. Tell him to come out now. You might ask him if you called the electrical inspector would the inspector test it for you. He won't, but you won't get that far. You can also narrow the search through a process of elimination. You could disconnect and cap each fixture one at a time, starting with the last in the chain, or disconnect them all and reconnect them one at a time. If they are all disconnected and the circuit still shorts: nail through a wire.
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I'll find your shorts for $500 per hour, (minimum 8 hours) plus my air-fare paid in advance, along with a $4000 down payment deposit. After I remove your shorts, I will expect the rest of the payment in full. Note, I will not return your shorts at the completion of the job, so don't ask for them. I always keep them for souvineers.
On 1 Mar 2006 19:42:18 -0800, "dale martin"

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