short?

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  #1  
Old 01-14-12, 04:12 AM
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short?

I appreciate any help troubleshooting this problem.
Basically,
-
  • An outlet went dead while the plumbers were using a jack hammer. We moved the jack hammer to another outlet to complete that job. There are no wires near where the jack hammer was being used to break the slab
  • there are 5 lights circuits and 1 outlet on the line.
  • meter shows 75 volts at the outlet when all the light switches are OFF
  • when ANY of the light switches are turned ON (with and without light bulbs removed) the voltage at the associated light socket shows 75 volts and the voltage at the outlet goes to zero.
  • with a long jumper from the main panel neutral to the outlet we get 120 V at the outlet, unaffected by the light switches.
  • outlet and 2 light switches replaced with no effect.
  • we do not see or smell any evidence of burned wires
  • the plumbers are blaming the house. The neighbor says the
    house is jealous of the new lawn.

Any help with the next step to take would be appreciated.
 
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  #2  
Old 01-14-12, 05:50 AM
Tolyn Ironhand's Avatar
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You have an open, not a short.

Open up the junction boxes and start looking for an open neutral. Either the vibration, or the high amp draw of the jackhammer, opened up an splice on that circuit.
 
  #3  
Old 01-14-12, 06:40 AM
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Thanks. I checked all the boxes and found nothing amiss. In the process I noticed I have about 30 volts on the wires running from the light switches to the lights when the switches are off???
 
  #4  
Old 01-14-12, 06:47 AM
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Are you using a digital meter or analog? Less expensive digital meters are "fooled" by phantom voltage. You may be reading nothing.

Start at the panel and work you way to the end of the circuit and take reading along the way.
Is this a multiwire cable in the panel? (3 wire cable on two breakers)
 
  #5  
Old 01-14-12, 07:32 AM
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with a long jumper from the main panel neutral to the outlet we get 120 V at the outlet
That statement tells me your open, or loose connection you are looking for, is on a neutral (white) conductor.
 
  #6  
Old 01-14-12, 07:42 AM
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Thanks. I moved my neutral jumper to the light switch closest to the panel and everything is now working. That would tell me (a rookie) that the problem is between that switch and the main panel. BUT, that light switch appears to be a branch off the circuit as there is only one wire coming into it. If it's just a branch and everything downstream is OK I'm not sure where to look next. The next closest switch box looks very solid.
 
  #7  
Old 01-14-12, 08:25 AM
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Remove all wire nuts and look inside for corrosion or just replace with new ones. Move any back stabbed wires to the screws. http://www.doityourself.com/forum/el...rminology.html
 
  #8  
Old 01-15-12, 05:53 AM
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Thanks. All the screws in the neutral bus bar were 1/4 turn loose. Problem solved. Thanks for your help.
 

Last edited by phil888; 01-15-12 at 07:38 AM.
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