Electrical Wiring in the Home/stumped - 30v AC to AC Duct

Advertisement


Question
So here is a weird one.  We had a burning smell in our 3rd floor bedroom whenever we turned our first floor kitchen lights on.  An HVAC guy came out, tore our wall out (our AC unit is in the wall of our 3rd floor bedroom) and found melted AC ductwork.  The ductwork is flexible and has a wire wrapped around it to hold its shape.  

That ductwork (the melted one) had a voltage reading of 60 v AC on the wire, which also was found on the metal duct work that ran from the attic to the kitchen ceiling.  Yep -60 v at the ductwork.  

Background - the house was built in 1925 and the wiring in the kitchen is old - the kitchen ceiling has a metal mesh that through it to hold the plaster, wood, etc.  That metal mesh touches the ductwork and has become energized.   We have track lighting in the kitchen - flip the light switch in the kitchen (there are three switches) and the voltage to the ductwork goes away.

So we had an electrician out and he found a frayed wire, repaired it and put plastic anchors in to hold the track lighting in.  Now the voltage has dropped but it is still there.

If I hold the positive of a meter to the ductwork, light switch cover plates (they are metal), mesh in the ceiling or the duct outlet in the ceiling and then put my finger on the negative side of the meter I see 25 to 30 v AC.  Not 60 anymore but still - the rest of the house shows 2v AC (more or less) at the switch plate or other metal items when lights are on - while the kitchen is showing the 30ish.

Thoughts?  Other than tear out the ceiling, find out what's going on (mind you we have already spent over $1000 on this with the replacing of melted ductwork, electricians, etc.) or rewiring the kitchen, what are your thoughts?  Is this acceptable or is this an emergency situation that needs to be resolved regardless of cost?

Your feed back is appreciated.

Answer
Not as weird as you may think.
Remnant 30 volts sounds like ghost reading, especially since you said it shows up when you touch probe. I am guessing that means you are not otherwise grounded. Capacitive coupling.

If you hold the lead from an oscilloscope while standing in the middle of a room you can see a 60 cycle waveform from your body - coupling.

You are probably using a digital meter?

Run an extension cord from somewhere and try readings to hot, neutral and ground of cord.

I think you will find voltage goes away.

Use an analog meter and a solenoid-type tester. They ain't afraid of no ghosts!
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here

Electrical Wiring in the Home

All Answers


Answers by Expert:


Ask Experts

Volunteer


Robert Wilber

Expertise

Licensed Philadelphia electrician serving Delaware, Chester, Montgomery and Philadelphia County in Pennsylvania. I install and repair residential, commercial and industrial wiring and lighting. Troubleshooting and repair of problems that stump other people is my favorite. I am willing to help people figure out why things don`t work. I understand motor controls, transformers and machine wiring. I do not teach basics to novices or do free design work.

Experience

Experience in the area I have 44 years experience in residential, commercial and industrial electrical construction and repair, 480 volts and below. This is not to be confused with one week repeated two thousand times.

Education/Credentials
44 years experience in residential, commercial and industrial electrical construction and repair

©2016 About.com. All rights reserved.