Bad Power Source

Bad Power Source

I created this bad power source for my workbench to aid in debugging and validating some of the high
voltage projects I’ve been working on.   The goal is to be able to simulate various line faults while also providing a slightly safer environment for debugging.


  • Toggle Switches to break Hot, Neutral, Ground
  • Polarity switch to swap Hot and Neutral
  • Short Switch to short Neutral to Ground
  • Indicator light showing voltage differential going to the outlet. This acts as an on/off indicator.  Also, if this light is on but the GFCI light is off then the GFCI breaker must be tripped.  This also helps you quickly find out if another breaker upstream has been tripped.
  • GFCI Outlet.  With the toggle switches in nominal positions the GFCI outlet will provide additional safety when probing around my high voltage projects. Note: this GFCI outlet will not function properly when the toggles are configured for a fault condition.
  • I like to keep one of my outlet testers plugged in to show the line configuration.

 Pictures of the Build

    An Old-Work Junction Box is the enclosure

    Right Toggle Switches
    Left Toggle Switches


    Stuffing it all together

    Other Accessories

    Here are a few other DIY accessories I use with my Bad Power Source. 

    NEMA 5-15 Plug to Banana Jacks
    Split-Rail Extension Cable for Current Monitoring

    My Full Test Bench

    Connected in the following order:

    1. Bench Power (Conditioned, surge protected, breaker)
    2. Bad Power Source
    3. Variable Transformer with 3way outlet for voltage monitoring.
    4. Split-Rail Extension Cable with current meter
    5. Device Under Test. (I used a lamp in this picture)
    Complete Bad Power Test Bench

    Future Ideas

    • Add a Hot to Ground polarity toggle switch.
    • Add an indicator lights before the hot switch to indicate incoming line voltage.
    • Full isolation transformer so it is safe to probe with my oscilloscope.
    • Step up transformer for 220V verification.

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