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It seems I lost a power from one of phases feeding the panel. The pen tester proofs that. It's interesting if I reset the main switch, the power comes back. If I put any appliance (be it a small light bulb) the power disappears on the same phase until main switch is turned -> off -> on.

I was wondering someone has any theories what could be the issue?

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    Do you have the service panel cover off? Make sure to shut off every 240V breaker or it can give you false readings. – Harper Jun 21 '18 at 14:56
  • I disconnected every 240v breaker and capped the wires inside. – bioffe Jun 21 '18 at 14:58
  • Have you checked on the supply side of the main breaker or just the output side. Breakers do go bad, I have had quality main breakers loose a leg. Sometimes turning the breaker on and off 10+ times with all the breakers turned off will clean and reseat the hammers in the breaker, if this works be prepared to buy a new breaker and replace or you will have the same problem in the future. – Ed Beal Jun 21 '18 at 16:31
  • Nope. Supply side of the main switch is beyond my comfort level as an average Joe homeowner. I am trying to understand science of this phenomena before I pay $000 dollars to electrician for a piece of advice. – bioffe Jun 21 '18 at 18:36
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    If it's on the supply side of the meter, it's the power company's responsibility and the bill will be $0.00. Calling them is free, I would try it. – Harper Jun 21 '18 at 21:14
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Most likely scenario: your main has a connection to the bus inside of the panel that distributes the power to all of the other feeder breakers. That connection is likely bad / corroded / burned, something that is creating high resistance. With no lod, your tick tracer picks up that there is voltage present, but as soon as you apply a load to it, the resistance causes the voltage to drop to effectively zero. Resetting the main breaker wiggles it a little to make just enough of a connection to satisfy that tick tracer, but that's it.

This is your life and safety involved here, the next phase of development of this problem may be a fire. you need to call an electrician.

  • I was thinking along the same line. Thanks for the clear explanation. If it is a corrosion issue, how come it happened in one day? I would rather expect this issue to become from incidental to systematic. I will try to deal with the main switch now. – bioffe Jun 22 '18 at 17:43
  • It could have been incremental, but one day, you hit the threshold. But you're right, that points more toward damage from it being loose and there is a build-up of carbon from arcing that has now reached a point of high resistance. – J. Raefield Jun 22 '18 at 22:59

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