The circuit powers an LED light. Using a multi meter connected to the two screws which hold down the white and black cables, the switch reads as "OL" or as "_/__" when checking for resistivity or continuity, respectively. The plug is then connected to mains voltage. The LED illuminates. Flipping the switch immediately causes the breaker to emit a spark and to pop. Once flipped, the switch reads as a 0 Ohms or "____" when checking for resistivity or continuity, respectively.

What is causing the breaker to pop? Is this safe to wire into my house? Why is the switch acting opposite to how I would have expected? That breaker is not part of the final wiring, I have it as a way to safely connect to mains voltage without needing to cut a lot of extra wire.

  • The socket is confirmed to be wired correctly by a receptacle tester
  • When connecting to mains voltage with the switch flipped, there is a spark at the socket (which caused some minor damage to the plug, I don't want to do that again)
  • The AC to DC converter is visible below, it is rated for 85V - 265V AC 50/60 Hz

The image shows the circuit not connected, that was simply for the picture. The whites were connected, as were the black cables.

Circuit Design - Drawn Circuit Design - Image

  • 2
    \$\begingroup\$ For your own safety and the safety of this around you, please stop playing with mains electricity until you've spent a lot more time learning with lower voltage, lower power, circuits. \$\endgroup\$
    – brhans
    Commented Oct 8, 2022 at 3:43
  • \$\begingroup\$ I appreciate the feedback. I made a stupid mistake, and took that very seriously. I spent the time to try to understand and sought help. I'd rather work with low voltage (less than 50V) but between sourcing equipment that works at that voltage, and generating that voltage, it isn't easy for most people to learn without using mains. \$\endgroup\$
    – TeckFudge
    Commented Oct 8, 2022 at 5:00
  • \$\begingroup\$ Batteries & LEDs (with appropriate resistors) would be a much safer starting point. \$\endgroup\$
    – brhans
    Commented Oct 8, 2022 at 13:41

1 Answer 1


From your photo, it appears that you have the switch across the incoming AC power, in parallel with the LED supply - like so:


simulate this circuit – Schematic created using CircuitLab

This way, the switch provides a short circuit across the supply when you turn it on.

You must instead connect the switch in series with the load, like so:


simulate this circuit

  • \$\begingroup\$ Thank you! I was certain that the issue lie with the light, or the breaker, or anything other than my wiring. The diagram you provided makes it so obvious what I was doing wrong. The one I made shows the problem very clearly too. I was just unable to see it. \$\endgroup\$
    – TeckFudge
    Commented Oct 8, 2022 at 3:02
  • \$\begingroup\$ @TeckFudge Remember that switches generally should only be installed in series with one line, the live. Neutral should never be switched. (switch all three live phases in a three-phase system, though.) \$\endgroup\$
    – Hearth
    Commented Oct 8, 2022 at 3:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.