100 foot scopemeter probe leads

Discussion in 'General Electronics Chat' started by melectrician, Apr 2, 2012.

  1. melectrician

    Thread Starter New Member

    Apr 2, 2012
    I am trying to make sense of some waveforms taken by another person with a Fluke Scopemeter. The measurement was taken between the electrical panel neutral and a remote ground rod. With variable frequency drives and electronic ballasts I would expect to see waveforms resulting from the switching power supplies and the vfd transistors switching but the waveforms seem quite a bit more erratic than I would have expected. The person who recorded the neutral voltage extended the leads of his Fluke 190 Scopemeter with 100 feet of RG 59 coax. He stripped back both ends of the coax and removed several inches of the shield on both ends. So, the shield is not connected but is floating. The coax center conductor was connected between the scope input and the electrical panel neutral. The ground connection to the scopemeter was another RG59 (with the shield floating) that was run 200 feet to a remote ground rod. I am thinking this was very wrong! Do you think this setup might work? How should it have been connected? What kind of erroneous readings (if any) might this type of configuration pick up? Any insight would be appreciated. Thanks!!!
  2. MrChips


    Oct 2, 2009
    He should have grounded at least one end of the coax shield.