A circuit is a loop
Current needs a full loop to flow. It goes out from the source, through the lamp, and comes back. You open the switch or break a wire and watch the current stop everywhere at once.
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What to try
- 1On Battery and lamp, compare Current going out with Current coming back. They match, because the lamp does not use up any current.
- 2Set Switch to Off. Then set it back to On and set Broken wire to Coming back. Either way the loop is open and the lamp goes dark.
- 3Pick Lamp plugged into 120 V and set Broken wire to Coming back. The lamp is dark, but it is still live and can shock you.
NEC 2026 sections it covers
- 240.4(D)
- 14 AWG copper gets a 15 A breaker at most.
- 210.12(B)
- Most rooms in a home also need AFCI protection.
Section numbers only. Read the full text in your code book. Temperatures and times in the visual are teaching models.
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More visuals
- Conductors and insulatorsPut copper, aluminum, rubber, or skin on the meter and see how hard each one makes it for current to get through.
- Volts, amps, and ohmsChange the voltage or the heater and watch the amps follow. Amps equal volts divided by ohms.
- Why you get shockedA shock happens when your body joins two points at different voltages. See why a breaker never notices it and a GFCI does.