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Old 08-29-2010, 04:53 PM   #1
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How to best diagnose and repair electrical issue.


Hi, a little background:

I live in a very old house. I rent, so I pretty much have to deal with what I've got unless something is demonstrably broken. I live on the 2nd and 3rd floor of the building; another tenant lives on the 1st floor. The original wiring is Knob & Tube, but much of it has been updated with a ground. The third floor received the least amount of new wiring.

I have only one grounded circuit on my third floor. I have a decent-size UPS unit plugged into the outlet which connects to my computer. The other outlet in the receptacle powers my AC during the summer. The ground-fault LED on the back of the UPS does not come on (as it does for some other outlets that were only updated with 3-prong receptacles but no ground) so I assume the wiring is sound. The problem appeared when I connected a touch-sensitive lamp to the outlet. It cycles through on and off every 5-10 seconds. This doesn't happen on any of the K&T outlets in this room, and I unplugged everything else from the grounded outlet to make sure that my computer or AC weren't causing the problem.

Wondering what my next steps are? It seems like maybe the voltage is fluctuating enough to trigger the lamp and Im worried that this will eventually fry my computer. Thanks!

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Old 08-29-2010, 06:08 PM   #2
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How to best diagnose and repair electrical issue.


Run your own ground, a #14 wire daisy chained from one piece of equipment (TV, computer, UPS, etc.) to another with the far end connected to a known ground which could be a radiator. Attach it to equipment either to a screw that goes through the cabinet to the chassis, or to the shell of an input jack that has such an outer shell.

Are you sure that your one grounded receptacle is indeed grounded? You can probably assume it is grounded by connecting a 100 watt incandescent light between hot and ground and then measuring the voltage across it for the proper 120 or so. Short wires with alligator clips on the ends can come in handy here.

Also you can check the voltage (hot to neutral) yourself at your convenience.

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Last edited by AllanJ; 08-29-2010 at 06:13 PM.
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Old 08-29-2010, 07:25 PM   #3
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How to best diagnose and repair electrical issue.


The NEC has rather specific rules about where a ground can be attached to ground a previously ungrounded receptacle. A radiator is not acceptable. You need to run back to the panel where the circuit originates or to the GEC for that panel.
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Old 08-29-2010, 07:50 PM   #4
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How to best diagnose and repair electrical issue.


Quote:
Originally Posted by adamjt View Post
The problem appeared when I connected a touch-sensitive lamp to the outlet. It cycles through on and off every 5-10 seconds.
It seems you have a very low frequency oscillator, 0.2 or 0.1 Hz.
If the lamp is ungrounded check the voltage variation to the lamp between hot & neutral. If there's no significant variation the lamp control may be bad.
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