Recent content by renaissanceEE

loops is short for ground loops. Having a good common ground source is is high importance when you have expensive electronics talking to each other over copper from distant ends of a building. You don't want that ground wire in twisted pair the shield in coax to be a different ground...

If I were to hazard a guess that #4 to the plumbing was the old building ground. A new good grounding source was most likely created when the telcom/computer equipment was installed and the old cut at the clamp to stop any possible loops.

Brings back memories I first saw the same thing two years ago at a buddy's house. Just picture two Electrical Engineers trying to fix a messed up 3-way in a 100 year old house, puzzling over why we were seeing 38 or so Volts on the red. Then it hit us, DUH it was just induced and...