Renting an older home and upon moving in was saddened to see outlets without grounds (two prongs). So, for one of the outlets I bought a 2 to 3 prong with ground clip and ran the ground to some vent duct work (resistance was less than 20 ohms per recommendations I've read). After plugging in surge protector (ground light turns on) and plugging in a two pronged TV, everything works, however, I was surprised to find that my voltage detector picked up energy on ground. It's not 110V, but its something, not 100% sure how much because my meter is broken.

Is this normal? Is this just the surge protector should bring extra fluctuations down the ground? The strange part is this only happens when I actually plug a device into the surge protector.

  • 5
    Voltage from ground to what?
    – Samuel
    Oct 7, 2013 at 3:00
  • So you're basically saying: "My broken meter measures something between a lump of ducting and some unknown reference point, please help."
    – John U
    Oct 7, 2013 at 8:37
  • I'd skip my morning coffee & donut and use the money to buy a receptacle tester instead. Oct 7, 2013 at 10:21
  • I'm fairly sure surge protectors work by dump surges to the grounding conductor, so I'd say it's working as designed. If you're seeing excess voltage on the ground of the surge protector, you should have the electrical system checked for excessive spikes.
    – Tester101
    Oct 7, 2013 at 14:04

1 Answer 1


More information needed.

What do you measure "energy on ground" RELATIVE TO ?
If it was a hard ground you'd see 100 VAC from lobe to ground. If it is a low resistance ground your meter resistance will affect the result.

For a metwer connected from Vmains to "ground" Vreading = Vmains x Rground / (Rground + Rmeter)

Some testers measure to local capacitive ground - sometimes the user touches a rear contact as a reference and their body capacity to "ground" is used as a reference. (Try not to "test" 10 kV circuits using these )

You say vent duct work resistance (to "true" ground?) was 20 Ohms. How do you know?

Be aware that by adding a low quality local ground you may INCREASE the risk of electric shock. See my answer to How does earthing work when earth is dry? to see why.

  • I detected voltage on ground using a voltage detector (one of those pens, tests from 50-1000V AC CAT III / 50-600V AC CAT IV). I know this isn't the most reliable method of measuring voltage, I just find it peculiar that it detects voltage on my ground to the venting only when I have something plugged into the surge. I know the duct is < 20ohm b/c I ran another temp ground wire to a pole in ground outside and tested the resistance between that pole and duct. Thanks for the link, I'm still digesting your comment there. Oct 7, 2013 at 14:12

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