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Circuit protection: breakers, shorts and GFCIs
Follow current around a branch circuit and see what a breaker and a GFCI do in an overload, a short circuit and a ground fault, and how to prove power is off.
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1. A circuit is a loop
Power leaves the panel on a hot wire, passes through the load, and returns on the neutral wire. The ground wire carries nothing in normal use. It is a safety path. Here the glowing beads are shown flowing one way: real household current reverses 60 times a second.
2. The breaker protects the wire
A breaker is sized to the wire, not to the appliance. Too much current heats a wire, and a hot wire can start a fire. The breaker trips before the wire gets dangerous: 15 amps for the common 14 gauge copper, 20 amps for 12 gauge.
3. Overload
Plug in too much and the current climbs past the circuit's rating. The wire warms, and a heat-sensitive strip inside the breaker bends until it trips. The wire glows here only to show the heat building: a correct breaker acts long before real damage.
4. Short circuit
If a hot conductor touches a neutral or ground, there is almost nothing to hold the current back. It surges to hundreds of amps in an instant. A magnet inside the breaker snaps it off in a fraction of a second, which is why a trip with a bang is the breaker doing its job.
5. Ground fault and the GFCI
A breaker will not notice a small current leaking through a person. A GFCI compares the current going out on the hot wire with the current coming back on the neutral. If a few thousandths of an amp go missing, it assumes they are going through someone and cuts power in a fraction of a second.
6. Prove it dead: live, dead, live
Switching a breaker off is not proof. Lock and tag it, then test: first the meter on a known live source to prove the meter works, then the circuit you will touch, which should read zero, then the known source again. Only then is it safe to work.
7. Never fit a bigger breaker
If a breaker keeps tripping, the circuit is telling you something. Swapping in a larger breaker removes the protection: the wire carries more current than it is rated for, heats up, and can ignite what surrounds it. Find the cause instead.
Hands-on practice
Make a circuit safe, then prove it
You are an electrician about to replace a worn outlet on a 15 amp circuit. Cut the power, secure it and prove it is dead before you touch anything.
Click the Practice button in the player. You click parts in the 3D model and make the calls a technician would, with hints, feedback and a star score. Inside SOPpal, finishing a task earns XP.
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