The title is a bit cumbersome because my questions are a bit difficult to describe. Here is a photo from Practical Electronics for Inventors by Paul Scherz

enter image description here

I'm curious on a few things:

  1. How does the BNC cable for the oscilloscope actually work? Since the ground and the hot wiring are not connected to each other, how does a potential between the two elicit energy/work?
  2. What does the neutral wiring actually do?
  3. For the DC Power Supply, why do we have a ground, negative and positive? What exactly does positive and negative actually do here? Electrons are negative or positive in terms technical direction of current.

Any insight or resources on these topics is appreciated.

  • \$\begingroup\$ The ground wire is connected to the scopes reference ground on the isolated side of its power supply. \$\endgroup\$ May 17, 2019 at 9:25
  • 1
    \$\begingroup\$ This is all described in the image. You need to start with a simpler question. \$\endgroup\$ May 17, 2019 at 9:37
  • \$\begingroup\$ Electrons are always negative.... always have been... always will be.... hopefully \$\endgroup\$
    – andowt
    May 17, 2019 at 12:37
  • \$\begingroup\$ You know what I meant... \$\endgroup\$
    – mikanim
    May 17, 2019 at 19:27
  • \$\begingroup\$ Neutral is connected to earth ground at one location (not shown in the diagram) at the main electrical panel. Since the return currents flow through neutral (not earth ground), each of the outlets develops a small potential difference between its neutral and earth ground. Typically around 10-20Vrms is what I’ve seen, but it will vary with the branch load currents. Earth ground is intended to shield the active electronics without carrying any current, so all of the earth grounds are at the same potential. \$\endgroup\$
    – MarkU
    May 17, 2019 at 23:51

1 Answer 1


The only optional earth grounds shown here are the floating DC power supply +/- and the Audio/Visual device jumpers.

Neutral is the return current for AC line (hot) power. Earth ground is always connect to Neutral at the distribution transformer and sometimes elsewhere in the building Earth ground.


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